Commit | Line | Data |
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f41d911f PM |
1 | /* |
2 | * Read-Copy Update mechanism for mutual exclusion (tree-based version) | |
3 | * Internal non-public definitions that provide either classic | |
6cc68793 | 4 | * or preemptible semantics. |
f41d911f PM |
5 | * |
6 | * This program is free software; you can redistribute it and/or modify | |
7 | * it under the terms of the GNU General Public License as published by | |
8 | * the Free Software Foundation; either version 2 of the License, or | |
9 | * (at your option) any later version. | |
10 | * | |
11 | * This program is distributed in the hope that it will be useful, | |
12 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
14 | * GNU General Public License for more details. | |
15 | * | |
16 | * You should have received a copy of the GNU General Public License | |
87de1cfd PM |
17 | * along with this program; if not, you can access it online at |
18 | * http://www.gnu.org/licenses/gpl-2.0.html. | |
f41d911f PM |
19 | * |
20 | * Copyright Red Hat, 2009 | |
21 | * Copyright IBM Corporation, 2009 | |
22 | * | |
23 | * Author: Ingo Molnar <mingo@elte.hu> | |
24 | * Paul E. McKenney <paulmck@linux.vnet.ibm.com> | |
25 | */ | |
26 | ||
d9a3da06 | 27 | #include <linux/delay.h> |
3fbfbf7a | 28 | #include <linux/gfp.h> |
b626c1b6 | 29 | #include <linux/oom.h> |
62ab7072 | 30 | #include <linux/smpboot.h> |
4102adab | 31 | #include "../time/tick-internal.h" |
f41d911f | 32 | |
5b61b0ba | 33 | #ifdef CONFIG_RCU_BOOST |
61cfd097 | 34 | |
abaa93d9 | 35 | #include "../locking/rtmutex_common.h" |
21871d7e | 36 | |
61cfd097 PM |
37 | /* |
38 | * Control variables for per-CPU and per-rcu_node kthreads. These | |
39 | * handle all flavors of RCU. | |
40 | */ | |
41 | static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task); | |
42 | DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status); | |
43 | DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops); | |
44 | DEFINE_PER_CPU(char, rcu_cpu_has_work); | |
45 | ||
727b705b PM |
46 | #else /* #ifdef CONFIG_RCU_BOOST */ |
47 | ||
48 | /* | |
49 | * Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST, | |
50 | * all uses are in dead code. Provide a definition to keep the compiler | |
51 | * happy, but add WARN_ON_ONCE() to complain if used in the wrong place. | |
52 | * This probably needs to be excluded from -rt builds. | |
53 | */ | |
54 | #define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; }) | |
55 | ||
56 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ | |
5b61b0ba | 57 | |
3fbfbf7a PM |
58 | #ifdef CONFIG_RCU_NOCB_CPU |
59 | static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ | |
60 | static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */ | |
1b0048a4 | 61 | static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ |
3fbfbf7a PM |
62 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ |
63 | ||
26845c28 PM |
64 | /* |
65 | * Check the RCU kernel configuration parameters and print informative | |
66 | * messages about anything out of the ordinary. If you like #ifdef, you | |
67 | * will love this function. | |
68 | */ | |
69 | static void __init rcu_bootup_announce_oddness(void) | |
70 | { | |
ab6f5bd6 PM |
71 | if (IS_ENABLED(CONFIG_RCU_TRACE)) |
72 | pr_info("\tRCU debugfs-based tracing is enabled.\n"); | |
05c5df31 PM |
73 | if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) || |
74 | (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32)) | |
ab6f5bd6 | 75 | pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n", |
05c5df31 | 76 | RCU_FANOUT); |
7fa27001 | 77 | if (rcu_fanout_exact) |
ab6f5bd6 PM |
78 | pr_info("\tHierarchical RCU autobalancing is disabled.\n"); |
79 | if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ)) | |
80 | pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n"); | |
81 | if (IS_ENABLED(CONFIG_PROVE_RCU)) | |
82 | pr_info("\tRCU lockdep checking is enabled.\n"); | |
83 | if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_RUNNABLE)) | |
84 | pr_info("\tRCU torture testing starts during boot.\n"); | |
42621697 AG |
85 | if (RCU_NUM_LVLS >= 4) |
86 | pr_info("\tFour(or more)-level hierarchy is enabled.\n"); | |
47d631af | 87 | if (RCU_FANOUT_LEAF != 16) |
a3bd2c09 | 88 | pr_info("\tBuild-time adjustment of leaf fanout to %d.\n", |
47d631af PM |
89 | RCU_FANOUT_LEAF); |
90 | if (rcu_fanout_leaf != RCU_FANOUT_LEAF) | |
9a5739d7 | 91 | pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf); |
cca6f393 | 92 | if (nr_cpu_ids != NR_CPUS) |
efc151c3 | 93 | pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids); |
ab6f5bd6 PM |
94 | if (IS_ENABLED(CONFIG_RCU_BOOST)) |
95 | pr_info("\tRCU kthread priority: %d.\n", kthread_prio); | |
26845c28 PM |
96 | } |
97 | ||
28f6569a | 98 | #ifdef CONFIG_PREEMPT_RCU |
f41d911f | 99 | |
a41bfeb2 | 100 | RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu); |
b28a7c01 | 101 | static struct rcu_state *const rcu_state_p = &rcu_preempt_state; |
2927a689 | 102 | static struct rcu_data __percpu *const rcu_data_p = &rcu_preempt_data; |
f41d911f | 103 | |
d9a3da06 | 104 | static int rcu_preempted_readers_exp(struct rcu_node *rnp); |
d19fb8d1 PM |
105 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, |
106 | bool wake); | |
d9a3da06 | 107 | |
f41d911f PM |
108 | /* |
109 | * Tell them what RCU they are running. | |
110 | */ | |
0e0fc1c2 | 111 | static void __init rcu_bootup_announce(void) |
f41d911f | 112 | { |
efc151c3 | 113 | pr_info("Preemptible hierarchical RCU implementation.\n"); |
26845c28 | 114 | rcu_bootup_announce_oddness(); |
f41d911f PM |
115 | } |
116 | ||
f41d911f | 117 | /* |
6cc68793 | 118 | * Record a preemptible-RCU quiescent state for the specified CPU. Note |
f41d911f PM |
119 | * that this just means that the task currently running on the CPU is |
120 | * not in a quiescent state. There might be any number of tasks blocked | |
121 | * while in an RCU read-side critical section. | |
25502a6c | 122 | * |
1d082fd0 PM |
123 | * As with the other rcu_*_qs() functions, callers to this function |
124 | * must disable preemption. | |
f41d911f | 125 | */ |
284a8c93 | 126 | static void rcu_preempt_qs(void) |
f41d911f | 127 | { |
2927a689 | 128 | if (!__this_cpu_read(rcu_data_p->passed_quiesce)) { |
284a8c93 | 129 | trace_rcu_grace_period(TPS("rcu_preempt"), |
2927a689 | 130 | __this_cpu_read(rcu_data_p->gpnum), |
284a8c93 | 131 | TPS("cpuqs")); |
2927a689 | 132 | __this_cpu_write(rcu_data_p->passed_quiesce, 1); |
284a8c93 PM |
133 | barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */ |
134 | current->rcu_read_unlock_special.b.need_qs = false; | |
135 | } | |
f41d911f PM |
136 | } |
137 | ||
138 | /* | |
c3422bea PM |
139 | * We have entered the scheduler, and the current task might soon be |
140 | * context-switched away from. If this task is in an RCU read-side | |
141 | * critical section, we will no longer be able to rely on the CPU to | |
12f5f524 PM |
142 | * record that fact, so we enqueue the task on the blkd_tasks list. |
143 | * The task will dequeue itself when it exits the outermost enclosing | |
144 | * RCU read-side critical section. Therefore, the current grace period | |
145 | * cannot be permitted to complete until the blkd_tasks list entries | |
146 | * predating the current grace period drain, in other words, until | |
147 | * rnp->gp_tasks becomes NULL. | |
c3422bea PM |
148 | * |
149 | * Caller must disable preemption. | |
f41d911f | 150 | */ |
38200cf2 | 151 | static void rcu_preempt_note_context_switch(void) |
f41d911f PM |
152 | { |
153 | struct task_struct *t = current; | |
c3422bea | 154 | unsigned long flags; |
f41d911f PM |
155 | struct rcu_data *rdp; |
156 | struct rcu_node *rnp; | |
157 | ||
10f39bb1 | 158 | if (t->rcu_read_lock_nesting > 0 && |
1d082fd0 | 159 | !t->rcu_read_unlock_special.b.blocked) { |
f41d911f PM |
160 | |
161 | /* Possibly blocking in an RCU read-side critical section. */ | |
e63c887c | 162 | rdp = this_cpu_ptr(rcu_state_p->rda); |
f41d911f | 163 | rnp = rdp->mynode; |
1304afb2 | 164 | raw_spin_lock_irqsave(&rnp->lock, flags); |
6303b9c8 | 165 | smp_mb__after_unlock_lock(); |
1d082fd0 | 166 | t->rcu_read_unlock_special.b.blocked = true; |
86848966 | 167 | t->rcu_blocked_node = rnp; |
f41d911f PM |
168 | |
169 | /* | |
170 | * If this CPU has already checked in, then this task | |
171 | * will hold up the next grace period rather than the | |
172 | * current grace period. Queue the task accordingly. | |
173 | * If the task is queued for the current grace period | |
174 | * (i.e., this CPU has not yet passed through a quiescent | |
175 | * state for the current grace period), then as long | |
176 | * as that task remains queued, the current grace period | |
12f5f524 PM |
177 | * cannot end. Note that there is some uncertainty as |
178 | * to exactly when the current grace period started. | |
179 | * We take a conservative approach, which can result | |
180 | * in unnecessarily waiting on tasks that started very | |
181 | * slightly after the current grace period began. C'est | |
182 | * la vie!!! | |
b0e165c0 PM |
183 | * |
184 | * But first, note that the current CPU must still be | |
185 | * on line! | |
f41d911f | 186 | */ |
0aa04b05 | 187 | WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0); |
e7d8842e | 188 | WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); |
12f5f524 PM |
189 | if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) { |
190 | list_add(&t->rcu_node_entry, rnp->gp_tasks->prev); | |
191 | rnp->gp_tasks = &t->rcu_node_entry; | |
727b705b PM |
192 | if (IS_ENABLED(CONFIG_RCU_BOOST) && |
193 | rnp->boost_tasks != NULL) | |
27f4d280 | 194 | rnp->boost_tasks = rnp->gp_tasks; |
12f5f524 PM |
195 | } else { |
196 | list_add(&t->rcu_node_entry, &rnp->blkd_tasks); | |
197 | if (rnp->qsmask & rdp->grpmask) | |
198 | rnp->gp_tasks = &t->rcu_node_entry; | |
199 | } | |
d4c08f2a PM |
200 | trace_rcu_preempt_task(rdp->rsp->name, |
201 | t->pid, | |
202 | (rnp->qsmask & rdp->grpmask) | |
203 | ? rnp->gpnum | |
204 | : rnp->gpnum + 1); | |
1304afb2 | 205 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
10f39bb1 | 206 | } else if (t->rcu_read_lock_nesting < 0 && |
1d082fd0 | 207 | t->rcu_read_unlock_special.s) { |
10f39bb1 PM |
208 | |
209 | /* | |
210 | * Complete exit from RCU read-side critical section on | |
211 | * behalf of preempted instance of __rcu_read_unlock(). | |
212 | */ | |
213 | rcu_read_unlock_special(t); | |
f41d911f PM |
214 | } |
215 | ||
216 | /* | |
217 | * Either we were not in an RCU read-side critical section to | |
218 | * begin with, or we have now recorded that critical section | |
219 | * globally. Either way, we can now note a quiescent state | |
220 | * for this CPU. Again, if we were in an RCU read-side critical | |
221 | * section, and if that critical section was blocking the current | |
222 | * grace period, then the fact that the task has been enqueued | |
223 | * means that we continue to block the current grace period. | |
224 | */ | |
284a8c93 | 225 | rcu_preempt_qs(); |
f41d911f PM |
226 | } |
227 | ||
fc2219d4 PM |
228 | /* |
229 | * Check for preempted RCU readers blocking the current grace period | |
230 | * for the specified rcu_node structure. If the caller needs a reliable | |
231 | * answer, it must hold the rcu_node's ->lock. | |
232 | */ | |
27f4d280 | 233 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 | 234 | { |
12f5f524 | 235 | return rnp->gp_tasks != NULL; |
fc2219d4 PM |
236 | } |
237 | ||
12f5f524 PM |
238 | /* |
239 | * Advance a ->blkd_tasks-list pointer to the next entry, instead | |
240 | * returning NULL if at the end of the list. | |
241 | */ | |
242 | static struct list_head *rcu_next_node_entry(struct task_struct *t, | |
243 | struct rcu_node *rnp) | |
244 | { | |
245 | struct list_head *np; | |
246 | ||
247 | np = t->rcu_node_entry.next; | |
248 | if (np == &rnp->blkd_tasks) | |
249 | np = NULL; | |
250 | return np; | |
251 | } | |
252 | ||
8af3a5e7 PM |
253 | /* |
254 | * Return true if the specified rcu_node structure has tasks that were | |
255 | * preempted within an RCU read-side critical section. | |
256 | */ | |
257 | static bool rcu_preempt_has_tasks(struct rcu_node *rnp) | |
258 | { | |
259 | return !list_empty(&rnp->blkd_tasks); | |
260 | } | |
261 | ||
b668c9cf PM |
262 | /* |
263 | * Handle special cases during rcu_read_unlock(), such as needing to | |
264 | * notify RCU core processing or task having blocked during the RCU | |
265 | * read-side critical section. | |
266 | */ | |
2a3fa843 | 267 | void rcu_read_unlock_special(struct task_struct *t) |
f41d911f | 268 | { |
b6a932d1 PM |
269 | bool empty_exp; |
270 | bool empty_norm; | |
271 | bool empty_exp_now; | |
f41d911f | 272 | unsigned long flags; |
12f5f524 | 273 | struct list_head *np; |
abaa93d9 | 274 | bool drop_boost_mutex = false; |
f41d911f | 275 | struct rcu_node *rnp; |
1d082fd0 | 276 | union rcu_special special; |
f41d911f PM |
277 | |
278 | /* NMI handlers cannot block and cannot safely manipulate state. */ | |
279 | if (in_nmi()) | |
280 | return; | |
281 | ||
282 | local_irq_save(flags); | |
283 | ||
284 | /* | |
285 | * If RCU core is waiting for this CPU to exit critical section, | |
1d082fd0 PM |
286 | * let it know that we have done so. Because irqs are disabled, |
287 | * t->rcu_read_unlock_special cannot change. | |
f41d911f PM |
288 | */ |
289 | special = t->rcu_read_unlock_special; | |
1d082fd0 | 290 | if (special.b.need_qs) { |
284a8c93 | 291 | rcu_preempt_qs(); |
c0135d07 | 292 | t->rcu_read_unlock_special.b.need_qs = false; |
1d082fd0 | 293 | if (!t->rcu_read_unlock_special.s) { |
79a62f95 LJ |
294 | local_irq_restore(flags); |
295 | return; | |
296 | } | |
f41d911f PM |
297 | } |
298 | ||
79a62f95 | 299 | /* Hardware IRQ handlers cannot block, complain if they get here. */ |
d24209bb PM |
300 | if (in_irq() || in_serving_softirq()) { |
301 | lockdep_rcu_suspicious(__FILE__, __LINE__, | |
302 | "rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n"); | |
303 | pr_alert("->rcu_read_unlock_special: %#x (b: %d, nq: %d)\n", | |
304 | t->rcu_read_unlock_special.s, | |
305 | t->rcu_read_unlock_special.b.blocked, | |
306 | t->rcu_read_unlock_special.b.need_qs); | |
f41d911f PM |
307 | local_irq_restore(flags); |
308 | return; | |
309 | } | |
310 | ||
311 | /* Clean up if blocked during RCU read-side critical section. */ | |
1d082fd0 PM |
312 | if (special.b.blocked) { |
313 | t->rcu_read_unlock_special.b.blocked = false; | |
f41d911f | 314 | |
dd5d19ba | 315 | /* |
0a0ba1c9 PM |
316 | * Remove this task from the list it blocked on. The task |
317 | * now remains queued on the rcu_node corresponding to | |
318 | * the CPU it first blocked on, so the first attempt to | |
319 | * acquire the task's rcu_node's ->lock will succeed. | |
320 | * Keep the loop and add a WARN_ON() out of sheer paranoia. | |
dd5d19ba PM |
321 | */ |
322 | for (;;) { | |
86848966 | 323 | rnp = t->rcu_blocked_node; |
1304afb2 | 324 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
6303b9c8 | 325 | smp_mb__after_unlock_lock(); |
86848966 | 326 | if (rnp == t->rcu_blocked_node) |
dd5d19ba | 327 | break; |
0a0ba1c9 | 328 | WARN_ON_ONCE(1); |
1304afb2 | 329 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
dd5d19ba | 330 | } |
74e871ac | 331 | empty_norm = !rcu_preempt_blocked_readers_cgp(rnp); |
d9a3da06 PM |
332 | empty_exp = !rcu_preempted_readers_exp(rnp); |
333 | smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ | |
12f5f524 | 334 | np = rcu_next_node_entry(t, rnp); |
f41d911f | 335 | list_del_init(&t->rcu_node_entry); |
82e78d80 | 336 | t->rcu_blocked_node = NULL; |
f7f7bac9 | 337 | trace_rcu_unlock_preempted_task(TPS("rcu_preempt"), |
d4c08f2a | 338 | rnp->gpnum, t->pid); |
12f5f524 PM |
339 | if (&t->rcu_node_entry == rnp->gp_tasks) |
340 | rnp->gp_tasks = np; | |
341 | if (&t->rcu_node_entry == rnp->exp_tasks) | |
342 | rnp->exp_tasks = np; | |
727b705b PM |
343 | if (IS_ENABLED(CONFIG_RCU_BOOST)) { |
344 | if (&t->rcu_node_entry == rnp->boost_tasks) | |
345 | rnp->boost_tasks = np; | |
346 | /* Snapshot ->boost_mtx ownership w/rnp->lock held. */ | |
347 | drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t; | |
348 | } | |
f41d911f PM |
349 | |
350 | /* | |
351 | * If this was the last task on the current list, and if | |
352 | * we aren't waiting on any CPUs, report the quiescent state. | |
389abd48 PM |
353 | * Note that rcu_report_unblock_qs_rnp() releases rnp->lock, |
354 | * so we must take a snapshot of the expedited state. | |
f41d911f | 355 | */ |
389abd48 | 356 | empty_exp_now = !rcu_preempted_readers_exp(rnp); |
74e871ac | 357 | if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) { |
f7f7bac9 | 358 | trace_rcu_quiescent_state_report(TPS("preempt_rcu"), |
d4c08f2a PM |
359 | rnp->gpnum, |
360 | 0, rnp->qsmask, | |
361 | rnp->level, | |
362 | rnp->grplo, | |
363 | rnp->grphi, | |
364 | !!rnp->gp_tasks); | |
e63c887c | 365 | rcu_report_unblock_qs_rnp(rcu_state_p, rnp, flags); |
c701d5d9 | 366 | } else { |
d4c08f2a | 367 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
c701d5d9 | 368 | } |
d9a3da06 | 369 | |
27f4d280 | 370 | /* Unboost if we were boosted. */ |
727b705b | 371 | if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex) |
abaa93d9 | 372 | rt_mutex_unlock(&rnp->boost_mtx); |
27f4d280 | 373 | |
d9a3da06 PM |
374 | /* |
375 | * If this was the last task on the expedited lists, | |
376 | * then we need to report up the rcu_node hierarchy. | |
377 | */ | |
389abd48 | 378 | if (!empty_exp && empty_exp_now) |
e63c887c | 379 | rcu_report_exp_rnp(rcu_state_p, rnp, true); |
b668c9cf PM |
380 | } else { |
381 | local_irq_restore(flags); | |
f41d911f | 382 | } |
f41d911f PM |
383 | } |
384 | ||
1ed509a2 PM |
385 | /* |
386 | * Dump detailed information for all tasks blocking the current RCU | |
387 | * grace period on the specified rcu_node structure. | |
388 | */ | |
389 | static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) | |
390 | { | |
391 | unsigned long flags; | |
1ed509a2 PM |
392 | struct task_struct *t; |
393 | ||
12f5f524 | 394 | raw_spin_lock_irqsave(&rnp->lock, flags); |
5fd4dc06 PM |
395 | if (!rcu_preempt_blocked_readers_cgp(rnp)) { |
396 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
397 | return; | |
398 | } | |
82efed06 | 399 | t = list_entry(rnp->gp_tasks->prev, |
12f5f524 PM |
400 | struct task_struct, rcu_node_entry); |
401 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) | |
402 | sched_show_task(t); | |
403 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
1ed509a2 PM |
404 | } |
405 | ||
406 | /* | |
407 | * Dump detailed information for all tasks blocking the current RCU | |
408 | * grace period. | |
409 | */ | |
410 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
411 | { | |
412 | struct rcu_node *rnp = rcu_get_root(rsp); | |
413 | ||
414 | rcu_print_detail_task_stall_rnp(rnp); | |
415 | rcu_for_each_leaf_node(rsp, rnp) | |
416 | rcu_print_detail_task_stall_rnp(rnp); | |
417 | } | |
418 | ||
a858af28 PM |
419 | static void rcu_print_task_stall_begin(struct rcu_node *rnp) |
420 | { | |
efc151c3 | 421 | pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", |
a858af28 PM |
422 | rnp->level, rnp->grplo, rnp->grphi); |
423 | } | |
424 | ||
425 | static void rcu_print_task_stall_end(void) | |
426 | { | |
efc151c3 | 427 | pr_cont("\n"); |
a858af28 PM |
428 | } |
429 | ||
f41d911f PM |
430 | /* |
431 | * Scan the current list of tasks blocked within RCU read-side critical | |
432 | * sections, printing out the tid of each. | |
433 | */ | |
9bc8b558 | 434 | static int rcu_print_task_stall(struct rcu_node *rnp) |
f41d911f | 435 | { |
f41d911f | 436 | struct task_struct *t; |
9bc8b558 | 437 | int ndetected = 0; |
f41d911f | 438 | |
27f4d280 | 439 | if (!rcu_preempt_blocked_readers_cgp(rnp)) |
9bc8b558 | 440 | return 0; |
a858af28 | 441 | rcu_print_task_stall_begin(rnp); |
82efed06 | 442 | t = list_entry(rnp->gp_tasks->prev, |
12f5f524 | 443 | struct task_struct, rcu_node_entry); |
9bc8b558 | 444 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { |
efc151c3 | 445 | pr_cont(" P%d", t->pid); |
9bc8b558 PM |
446 | ndetected++; |
447 | } | |
a858af28 | 448 | rcu_print_task_stall_end(); |
9bc8b558 | 449 | return ndetected; |
f41d911f PM |
450 | } |
451 | ||
b0e165c0 PM |
452 | /* |
453 | * Check that the list of blocked tasks for the newly completed grace | |
454 | * period is in fact empty. It is a serious bug to complete a grace | |
455 | * period that still has RCU readers blocked! This function must be | |
456 | * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock | |
457 | * must be held by the caller. | |
12f5f524 PM |
458 | * |
459 | * Also, if there are blocked tasks on the list, they automatically | |
460 | * block the newly created grace period, so set up ->gp_tasks accordingly. | |
b0e165c0 PM |
461 | */ |
462 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
463 | { | |
27f4d280 | 464 | WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); |
96e92021 | 465 | if (rcu_preempt_has_tasks(rnp)) |
12f5f524 | 466 | rnp->gp_tasks = rnp->blkd_tasks.next; |
28ecd580 | 467 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
468 | } |
469 | ||
f41d911f PM |
470 | /* |
471 | * Check for a quiescent state from the current CPU. When a task blocks, | |
472 | * the task is recorded in the corresponding CPU's rcu_node structure, | |
473 | * which is checked elsewhere. | |
474 | * | |
475 | * Caller must disable hard irqs. | |
476 | */ | |
86aea0e6 | 477 | static void rcu_preempt_check_callbacks(void) |
f41d911f PM |
478 | { |
479 | struct task_struct *t = current; | |
480 | ||
481 | if (t->rcu_read_lock_nesting == 0) { | |
284a8c93 | 482 | rcu_preempt_qs(); |
f41d911f PM |
483 | return; |
484 | } | |
10f39bb1 | 485 | if (t->rcu_read_lock_nesting > 0 && |
2927a689 PM |
486 | __this_cpu_read(rcu_data_p->qs_pending) && |
487 | !__this_cpu_read(rcu_data_p->passed_quiesce)) | |
1d082fd0 | 488 | t->rcu_read_unlock_special.b.need_qs = true; |
f41d911f PM |
489 | } |
490 | ||
a46e0899 PM |
491 | #ifdef CONFIG_RCU_BOOST |
492 | ||
09223371 SL |
493 | static void rcu_preempt_do_callbacks(void) |
494 | { | |
2927a689 | 495 | rcu_do_batch(rcu_state_p, this_cpu_ptr(rcu_data_p)); |
09223371 SL |
496 | } |
497 | ||
a46e0899 PM |
498 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
499 | ||
f41d911f | 500 | /* |
6cc68793 | 501 | * Queue a preemptible-RCU callback for invocation after a grace period. |
f41d911f PM |
502 | */ |
503 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) | |
504 | { | |
e63c887c | 505 | __call_rcu(head, func, rcu_state_p, -1, 0); |
f41d911f PM |
506 | } |
507 | EXPORT_SYMBOL_GPL(call_rcu); | |
508 | ||
6ebb237b PM |
509 | /** |
510 | * synchronize_rcu - wait until a grace period has elapsed. | |
511 | * | |
512 | * Control will return to the caller some time after a full grace | |
513 | * period has elapsed, in other words after all currently executing RCU | |
77d8485a PM |
514 | * read-side critical sections have completed. Note, however, that |
515 | * upon return from synchronize_rcu(), the caller might well be executing | |
516 | * concurrently with new RCU read-side critical sections that began while | |
517 | * synchronize_rcu() was waiting. RCU read-side critical sections are | |
518 | * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. | |
f0a0e6f2 PM |
519 | * |
520 | * See the description of synchronize_sched() for more detailed information | |
521 | * on memory ordering guarantees. | |
6ebb237b PM |
522 | */ |
523 | void synchronize_rcu(void) | |
524 | { | |
f78f5b90 PM |
525 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || |
526 | lock_is_held(&rcu_lock_map) || | |
527 | lock_is_held(&rcu_sched_lock_map), | |
528 | "Illegal synchronize_rcu() in RCU read-side critical section"); | |
6ebb237b PM |
529 | if (!rcu_scheduler_active) |
530 | return; | |
5afff48b | 531 | if (rcu_gp_is_expedited()) |
3705b88d AM |
532 | synchronize_rcu_expedited(); |
533 | else | |
534 | wait_rcu_gp(call_rcu); | |
6ebb237b PM |
535 | } |
536 | EXPORT_SYMBOL_GPL(synchronize_rcu); | |
537 | ||
d9a3da06 | 538 | static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); |
d9a3da06 PM |
539 | |
540 | /* | |
541 | * Return non-zero if there are any tasks in RCU read-side critical | |
542 | * sections blocking the current preemptible-RCU expedited grace period. | |
543 | * If there is no preemptible-RCU expedited grace period currently in | |
544 | * progress, returns zero unconditionally. | |
545 | */ | |
546 | static int rcu_preempted_readers_exp(struct rcu_node *rnp) | |
547 | { | |
12f5f524 | 548 | return rnp->exp_tasks != NULL; |
d9a3da06 PM |
549 | } |
550 | ||
551 | /* | |
552 | * return non-zero if there is no RCU expedited grace period in progress | |
553 | * for the specified rcu_node structure, in other words, if all CPUs and | |
554 | * tasks covered by the specified rcu_node structure have done their bit | |
555 | * for the current expedited grace period. Works only for preemptible | |
556 | * RCU -- other RCU implementation use other means. | |
557 | * | |
29fd9309 | 558 | * Caller must hold the root rcu_node's exp_funnel_mutex. |
d9a3da06 PM |
559 | */ |
560 | static int sync_rcu_preempt_exp_done(struct rcu_node *rnp) | |
561 | { | |
562 | return !rcu_preempted_readers_exp(rnp) && | |
7d0ae808 | 563 | READ_ONCE(rnp->expmask) == 0; |
d9a3da06 PM |
564 | } |
565 | ||
566 | /* | |
567 | * Report the exit from RCU read-side critical section for the last task | |
568 | * that queued itself during or before the current expedited preemptible-RCU | |
569 | * grace period. This event is reported either to the rcu_node structure on | |
570 | * which the task was queued or to one of that rcu_node structure's ancestors, | |
571 | * recursively up the tree. (Calm down, calm down, we do the recursion | |
572 | * iteratively!) | |
573 | * | |
29fd9309 | 574 | * Caller must hold the root rcu_node's exp_funnel_mutex. |
d9a3da06 | 575 | */ |
b40d293e TG |
576 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, |
577 | bool wake) | |
d9a3da06 PM |
578 | { |
579 | unsigned long flags; | |
580 | unsigned long mask; | |
581 | ||
1304afb2 | 582 | raw_spin_lock_irqsave(&rnp->lock, flags); |
6303b9c8 | 583 | smp_mb__after_unlock_lock(); |
d9a3da06 | 584 | for (;;) { |
131906b0 PM |
585 | if (!sync_rcu_preempt_exp_done(rnp)) { |
586 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
d9a3da06 | 587 | break; |
131906b0 | 588 | } |
d9a3da06 | 589 | if (rnp->parent == NULL) { |
131906b0 | 590 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
78e4bc34 PM |
591 | if (wake) { |
592 | smp_mb(); /* EGP done before wake_up(). */ | |
b40d293e | 593 | wake_up(&sync_rcu_preempt_exp_wq); |
78e4bc34 | 594 | } |
d9a3da06 PM |
595 | break; |
596 | } | |
597 | mask = rnp->grpmask; | |
1304afb2 | 598 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ |
d9a3da06 | 599 | rnp = rnp->parent; |
1304afb2 | 600 | raw_spin_lock(&rnp->lock); /* irqs already disabled */ |
6303b9c8 | 601 | smp_mb__after_unlock_lock(); |
d9a3da06 PM |
602 | rnp->expmask &= ~mask; |
603 | } | |
d9a3da06 PM |
604 | } |
605 | ||
606 | /* | |
607 | * Snapshot the tasks blocking the newly started preemptible-RCU expedited | |
8eb74b2b PM |
608 | * grace period for the specified rcu_node structure, phase 1. If there |
609 | * are such tasks, set the ->expmask bits up the rcu_node tree and also | |
610 | * set the ->expmask bits on the leaf rcu_node structures to tell phase 2 | |
611 | * that work is needed here. | |
d9a3da06 | 612 | * |
29fd9309 | 613 | * Caller must hold the root rcu_node's exp_funnel_mutex. |
d9a3da06 PM |
614 | */ |
615 | static void | |
8eb74b2b | 616 | sync_rcu_preempt_exp_init1(struct rcu_state *rsp, struct rcu_node *rnp) |
d9a3da06 | 617 | { |
1217ed1b | 618 | unsigned long flags; |
8eb74b2b PM |
619 | unsigned long mask; |
620 | struct rcu_node *rnp_up; | |
d9a3da06 | 621 | |
1217ed1b | 622 | raw_spin_lock_irqsave(&rnp->lock, flags); |
6303b9c8 | 623 | smp_mb__after_unlock_lock(); |
8eb74b2b PM |
624 | WARN_ON_ONCE(rnp->expmask); |
625 | WARN_ON_ONCE(rnp->exp_tasks); | |
96e92021 | 626 | if (!rcu_preempt_has_tasks(rnp)) { |
8eb74b2b | 627 | /* No blocked tasks, nothing to do. */ |
1217ed1b | 628 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
8eb74b2b PM |
629 | return; |
630 | } | |
631 | /* Call for Phase 2 and propagate ->expmask bits up the tree. */ | |
632 | rnp->expmask = 1; | |
633 | rnp_up = rnp; | |
634 | while (rnp_up->parent) { | |
635 | mask = rnp_up->grpmask; | |
636 | rnp_up = rnp_up->parent; | |
637 | if (rnp_up->expmask & mask) | |
638 | break; | |
639 | raw_spin_lock(&rnp_up->lock); /* irqs already off */ | |
640 | smp_mb__after_unlock_lock(); | |
641 | rnp_up->expmask |= mask; | |
642 | raw_spin_unlock(&rnp_up->lock); /* irqs still off */ | |
643 | } | |
644 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
645 | } | |
646 | ||
647 | /* | |
648 | * Snapshot the tasks blocking the newly started preemptible-RCU expedited | |
649 | * grace period for the specified rcu_node structure, phase 2. If the | |
650 | * leaf rcu_node structure has its ->expmask field set, check for tasks. | |
651 | * If there are some, clear ->expmask and set ->exp_tasks accordingly, | |
652 | * then initiate RCU priority boosting. Otherwise, clear ->expmask and | |
653 | * invoke rcu_report_exp_rnp() to clear out the upper-level ->expmask bits, | |
654 | * enabling rcu_read_unlock_special() to do the bit-clearing. | |
655 | * | |
29fd9309 | 656 | * Caller must hold the root rcu_node's exp_funnel_mutex. |
8eb74b2b PM |
657 | */ |
658 | static void | |
659 | sync_rcu_preempt_exp_init2(struct rcu_state *rsp, struct rcu_node *rnp) | |
660 | { | |
661 | unsigned long flags; | |
662 | ||
663 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
664 | smp_mb__after_unlock_lock(); | |
665 | if (!rnp->expmask) { | |
666 | /* Phase 1 didn't do anything, so Phase 2 doesn't either. */ | |
667 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
668 | return; | |
669 | } | |
670 | ||
671 | /* Phase 1 is over. */ | |
672 | rnp->expmask = 0; | |
673 | ||
674 | /* | |
675 | * If there are still blocked tasks, set up ->exp_tasks so that | |
676 | * rcu_read_unlock_special() will wake us and then boost them. | |
677 | */ | |
678 | if (rcu_preempt_has_tasks(rnp)) { | |
12f5f524 | 679 | rnp->exp_tasks = rnp->blkd_tasks.next; |
1217ed1b | 680 | rcu_initiate_boost(rnp, flags); /* releases rnp->lock */ |
8eb74b2b | 681 | return; |
12f5f524 | 682 | } |
8eb74b2b PM |
683 | |
684 | /* No longer any blocked tasks, so undo bit setting. */ | |
685 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
686 | rcu_report_exp_rnp(rsp, rnp, false); | |
d9a3da06 PM |
687 | } |
688 | ||
236fefaf PM |
689 | /** |
690 | * synchronize_rcu_expedited - Brute-force RCU grace period | |
691 | * | |
692 | * Wait for an RCU-preempt grace period, but expedite it. The basic | |
693 | * idea is to invoke synchronize_sched_expedited() to push all the tasks to | |
694 | * the ->blkd_tasks lists and wait for this list to drain. This consumes | |
695 | * significant time on all CPUs and is unfriendly to real-time workloads, | |
696 | * so is thus not recommended for any sort of common-case code. | |
697 | * In fact, if you are using synchronize_rcu_expedited() in a loop, | |
698 | * please restructure your code to batch your updates, and then Use a | |
699 | * single synchronize_rcu() instead. | |
019129d5 PM |
700 | */ |
701 | void synchronize_rcu_expedited(void) | |
702 | { | |
d9a3da06 | 703 | struct rcu_node *rnp; |
29fd9309 | 704 | struct rcu_node *rnp_unlock; |
e63c887c | 705 | struct rcu_state *rsp = rcu_state_p; |
543c6158 | 706 | unsigned long s; |
d9a3da06 | 707 | |
543c6158 | 708 | s = rcu_exp_gp_seq_snap(rsp); |
d9a3da06 | 709 | |
29fd9309 PM |
710 | rnp_unlock = exp_funnel_lock(rsp, s); |
711 | if (rnp_unlock == NULL) | |
712 | return; /* Someone else did our work for us. */ | |
1943c89d | 713 | |
543c6158 | 714 | rcu_exp_gp_seq_start(rsp); |
d9a3da06 | 715 | |
12f5f524 | 716 | /* force all RCU readers onto ->blkd_tasks lists. */ |
d9a3da06 PM |
717 | synchronize_sched_expedited(); |
718 | ||
8eb74b2b PM |
719 | /* |
720 | * Snapshot current state of ->blkd_tasks lists into ->expmask. | |
721 | * Phase 1 sets bits and phase 2 permits rcu_read_unlock_special() | |
722 | * to start clearing them. Doing this in one phase leads to | |
723 | * strange races between setting and clearing bits, so just say "no"! | |
724 | */ | |
d9a3da06 | 725 | rcu_for_each_leaf_node(rsp, rnp) |
8eb74b2b | 726 | sync_rcu_preempt_exp_init1(rsp, rnp); |
d9a3da06 | 727 | rcu_for_each_leaf_node(rsp, rnp) |
8eb74b2b | 728 | sync_rcu_preempt_exp_init2(rsp, rnp); |
d9a3da06 | 729 | |
12f5f524 | 730 | /* Wait for snapshotted ->blkd_tasks lists to drain. */ |
d9a3da06 PM |
731 | rnp = rcu_get_root(rsp); |
732 | wait_event(sync_rcu_preempt_exp_wq, | |
733 | sync_rcu_preempt_exp_done(rnp)); | |
734 | ||
735 | /* Clean up and exit. */ | |
543c6158 | 736 | rcu_exp_gp_seq_end(rsp); |
29fd9309 | 737 | mutex_unlock(&rnp_unlock->exp_funnel_mutex); |
019129d5 PM |
738 | } |
739 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
740 | ||
e74f4c45 PM |
741 | /** |
742 | * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. | |
f0a0e6f2 PM |
743 | * |
744 | * Note that this primitive does not necessarily wait for an RCU grace period | |
745 | * to complete. For example, if there are no RCU callbacks queued anywhere | |
746 | * in the system, then rcu_barrier() is within its rights to return | |
747 | * immediately, without waiting for anything, much less an RCU grace period. | |
e74f4c45 PM |
748 | */ |
749 | void rcu_barrier(void) | |
750 | { | |
e63c887c | 751 | _rcu_barrier(rcu_state_p); |
e74f4c45 PM |
752 | } |
753 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
754 | ||
1eba8f84 | 755 | /* |
6cc68793 | 756 | * Initialize preemptible RCU's state structures. |
1eba8f84 PM |
757 | */ |
758 | static void __init __rcu_init_preempt(void) | |
759 | { | |
2927a689 | 760 | rcu_init_one(rcu_state_p, rcu_data_p); |
1eba8f84 PM |
761 | } |
762 | ||
2439b696 PM |
763 | /* |
764 | * Check for a task exiting while in a preemptible-RCU read-side | |
765 | * critical section, clean up if so. No need to issue warnings, | |
766 | * as debug_check_no_locks_held() already does this if lockdep | |
767 | * is enabled. | |
768 | */ | |
769 | void exit_rcu(void) | |
770 | { | |
771 | struct task_struct *t = current; | |
772 | ||
773 | if (likely(list_empty(¤t->rcu_node_entry))) | |
774 | return; | |
775 | t->rcu_read_lock_nesting = 1; | |
776 | barrier(); | |
1d082fd0 | 777 | t->rcu_read_unlock_special.b.blocked = true; |
2439b696 PM |
778 | __rcu_read_unlock(); |
779 | } | |
780 | ||
28f6569a | 781 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
f41d911f | 782 | |
b28a7c01 | 783 | static struct rcu_state *const rcu_state_p = &rcu_sched_state; |
2927a689 | 784 | static struct rcu_data __percpu *const rcu_data_p = &rcu_sched_data; |
27f4d280 | 785 | |
f41d911f PM |
786 | /* |
787 | * Tell them what RCU they are running. | |
788 | */ | |
0e0fc1c2 | 789 | static void __init rcu_bootup_announce(void) |
f41d911f | 790 | { |
efc151c3 | 791 | pr_info("Hierarchical RCU implementation.\n"); |
26845c28 | 792 | rcu_bootup_announce_oddness(); |
f41d911f PM |
793 | } |
794 | ||
cba6d0d6 PM |
795 | /* |
796 | * Because preemptible RCU does not exist, we never have to check for | |
797 | * CPUs being in quiescent states. | |
798 | */ | |
38200cf2 | 799 | static void rcu_preempt_note_context_switch(void) |
cba6d0d6 PM |
800 | { |
801 | } | |
802 | ||
fc2219d4 | 803 | /* |
6cc68793 | 804 | * Because preemptible RCU does not exist, there are never any preempted |
fc2219d4 PM |
805 | * RCU readers. |
806 | */ | |
27f4d280 | 807 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 PM |
808 | { |
809 | return 0; | |
810 | } | |
811 | ||
8af3a5e7 PM |
812 | /* |
813 | * Because there is no preemptible RCU, there can be no readers blocked. | |
814 | */ | |
815 | static bool rcu_preempt_has_tasks(struct rcu_node *rnp) | |
b668c9cf | 816 | { |
8af3a5e7 | 817 | return false; |
b668c9cf PM |
818 | } |
819 | ||
1ed509a2 | 820 | /* |
6cc68793 | 821 | * Because preemptible RCU does not exist, we never have to check for |
1ed509a2 PM |
822 | * tasks blocked within RCU read-side critical sections. |
823 | */ | |
824 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
825 | { | |
826 | } | |
827 | ||
f41d911f | 828 | /* |
6cc68793 | 829 | * Because preemptible RCU does not exist, we never have to check for |
f41d911f PM |
830 | * tasks blocked within RCU read-side critical sections. |
831 | */ | |
9bc8b558 | 832 | static int rcu_print_task_stall(struct rcu_node *rnp) |
f41d911f | 833 | { |
9bc8b558 | 834 | return 0; |
f41d911f PM |
835 | } |
836 | ||
b0e165c0 | 837 | /* |
6cc68793 | 838 | * Because there is no preemptible RCU, there can be no readers blocked, |
49e29126 PM |
839 | * so there is no need to check for blocked tasks. So check only for |
840 | * bogus qsmask values. | |
b0e165c0 PM |
841 | */ |
842 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
843 | { | |
49e29126 | 844 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
845 | } |
846 | ||
f41d911f | 847 | /* |
6cc68793 | 848 | * Because preemptible RCU does not exist, it never has any callbacks |
f41d911f PM |
849 | * to check. |
850 | */ | |
86aea0e6 | 851 | static void rcu_preempt_check_callbacks(void) |
f41d911f PM |
852 | { |
853 | } | |
854 | ||
019129d5 PM |
855 | /* |
856 | * Wait for an rcu-preempt grace period, but make it happen quickly. | |
6cc68793 | 857 | * But because preemptible RCU does not exist, map to rcu-sched. |
019129d5 PM |
858 | */ |
859 | void synchronize_rcu_expedited(void) | |
860 | { | |
861 | synchronize_sched_expedited(); | |
862 | } | |
863 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
864 | ||
e74f4c45 | 865 | /* |
6cc68793 | 866 | * Because preemptible RCU does not exist, rcu_barrier() is just |
e74f4c45 PM |
867 | * another name for rcu_barrier_sched(). |
868 | */ | |
869 | void rcu_barrier(void) | |
870 | { | |
871 | rcu_barrier_sched(); | |
872 | } | |
873 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
874 | ||
1eba8f84 | 875 | /* |
6cc68793 | 876 | * Because preemptible RCU does not exist, it need not be initialized. |
1eba8f84 PM |
877 | */ |
878 | static void __init __rcu_init_preempt(void) | |
879 | { | |
880 | } | |
881 | ||
2439b696 PM |
882 | /* |
883 | * Because preemptible RCU does not exist, tasks cannot possibly exit | |
884 | * while in preemptible RCU read-side critical sections. | |
885 | */ | |
886 | void exit_rcu(void) | |
887 | { | |
888 | } | |
889 | ||
28f6569a | 890 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
8bd93a2c | 891 | |
27f4d280 PM |
892 | #ifdef CONFIG_RCU_BOOST |
893 | ||
1696a8be | 894 | #include "../locking/rtmutex_common.h" |
27f4d280 | 895 | |
0ea1f2eb PM |
896 | #ifdef CONFIG_RCU_TRACE |
897 | ||
898 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) | |
899 | { | |
96e92021 | 900 | if (!rcu_preempt_has_tasks(rnp)) |
0ea1f2eb PM |
901 | rnp->n_balk_blkd_tasks++; |
902 | else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL) | |
903 | rnp->n_balk_exp_gp_tasks++; | |
904 | else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL) | |
905 | rnp->n_balk_boost_tasks++; | |
906 | else if (rnp->gp_tasks != NULL && rnp->qsmask != 0) | |
907 | rnp->n_balk_notblocked++; | |
908 | else if (rnp->gp_tasks != NULL && | |
a9f4793d | 909 | ULONG_CMP_LT(jiffies, rnp->boost_time)) |
0ea1f2eb PM |
910 | rnp->n_balk_notyet++; |
911 | else | |
912 | rnp->n_balk_nos++; | |
913 | } | |
914 | ||
915 | #else /* #ifdef CONFIG_RCU_TRACE */ | |
916 | ||
917 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) | |
918 | { | |
919 | } | |
920 | ||
921 | #endif /* #else #ifdef CONFIG_RCU_TRACE */ | |
922 | ||
5d01bbd1 TG |
923 | static void rcu_wake_cond(struct task_struct *t, int status) |
924 | { | |
925 | /* | |
926 | * If the thread is yielding, only wake it when this | |
927 | * is invoked from idle | |
928 | */ | |
929 | if (status != RCU_KTHREAD_YIELDING || is_idle_task(current)) | |
930 | wake_up_process(t); | |
931 | } | |
932 | ||
27f4d280 PM |
933 | /* |
934 | * Carry out RCU priority boosting on the task indicated by ->exp_tasks | |
935 | * or ->boost_tasks, advancing the pointer to the next task in the | |
936 | * ->blkd_tasks list. | |
937 | * | |
938 | * Note that irqs must be enabled: boosting the task can block. | |
939 | * Returns 1 if there are more tasks needing to be boosted. | |
940 | */ | |
941 | static int rcu_boost(struct rcu_node *rnp) | |
942 | { | |
943 | unsigned long flags; | |
27f4d280 PM |
944 | struct task_struct *t; |
945 | struct list_head *tb; | |
946 | ||
7d0ae808 PM |
947 | if (READ_ONCE(rnp->exp_tasks) == NULL && |
948 | READ_ONCE(rnp->boost_tasks) == NULL) | |
27f4d280 PM |
949 | return 0; /* Nothing left to boost. */ |
950 | ||
951 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
6303b9c8 | 952 | smp_mb__after_unlock_lock(); |
27f4d280 PM |
953 | |
954 | /* | |
955 | * Recheck under the lock: all tasks in need of boosting | |
956 | * might exit their RCU read-side critical sections on their own. | |
957 | */ | |
958 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { | |
959 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
960 | return 0; | |
961 | } | |
962 | ||
963 | /* | |
964 | * Preferentially boost tasks blocking expedited grace periods. | |
965 | * This cannot starve the normal grace periods because a second | |
966 | * expedited grace period must boost all blocked tasks, including | |
967 | * those blocking the pre-existing normal grace period. | |
968 | */ | |
0ea1f2eb | 969 | if (rnp->exp_tasks != NULL) { |
27f4d280 | 970 | tb = rnp->exp_tasks; |
0ea1f2eb PM |
971 | rnp->n_exp_boosts++; |
972 | } else { | |
27f4d280 | 973 | tb = rnp->boost_tasks; |
0ea1f2eb PM |
974 | rnp->n_normal_boosts++; |
975 | } | |
976 | rnp->n_tasks_boosted++; | |
27f4d280 PM |
977 | |
978 | /* | |
979 | * We boost task t by manufacturing an rt_mutex that appears to | |
980 | * be held by task t. We leave a pointer to that rt_mutex where | |
981 | * task t can find it, and task t will release the mutex when it | |
982 | * exits its outermost RCU read-side critical section. Then | |
983 | * simply acquiring this artificial rt_mutex will boost task | |
984 | * t's priority. (Thanks to tglx for suggesting this approach!) | |
985 | * | |
986 | * Note that task t must acquire rnp->lock to remove itself from | |
987 | * the ->blkd_tasks list, which it will do from exit() if from | |
988 | * nowhere else. We therefore are guaranteed that task t will | |
989 | * stay around at least until we drop rnp->lock. Note that | |
990 | * rnp->lock also resolves races between our priority boosting | |
991 | * and task t's exiting its outermost RCU read-side critical | |
992 | * section. | |
993 | */ | |
994 | t = container_of(tb, struct task_struct, rcu_node_entry); | |
abaa93d9 | 995 | rt_mutex_init_proxy_locked(&rnp->boost_mtx, t); |
27f4d280 | 996 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
abaa93d9 PM |
997 | /* Lock only for side effect: boosts task t's priority. */ |
998 | rt_mutex_lock(&rnp->boost_mtx); | |
999 | rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */ | |
27f4d280 | 1000 | |
7d0ae808 PM |
1001 | return READ_ONCE(rnp->exp_tasks) != NULL || |
1002 | READ_ONCE(rnp->boost_tasks) != NULL; | |
27f4d280 PM |
1003 | } |
1004 | ||
27f4d280 | 1005 | /* |
bc17ea10 | 1006 | * Priority-boosting kthread, one per leaf rcu_node. |
27f4d280 PM |
1007 | */ |
1008 | static int rcu_boost_kthread(void *arg) | |
1009 | { | |
1010 | struct rcu_node *rnp = (struct rcu_node *)arg; | |
1011 | int spincnt = 0; | |
1012 | int more2boost; | |
1013 | ||
f7f7bac9 | 1014 | trace_rcu_utilization(TPS("Start boost kthread@init")); |
27f4d280 | 1015 | for (;;) { |
d71df90e | 1016 | rnp->boost_kthread_status = RCU_KTHREAD_WAITING; |
f7f7bac9 | 1017 | trace_rcu_utilization(TPS("End boost kthread@rcu_wait")); |
08bca60a | 1018 | rcu_wait(rnp->boost_tasks || rnp->exp_tasks); |
f7f7bac9 | 1019 | trace_rcu_utilization(TPS("Start boost kthread@rcu_wait")); |
d71df90e | 1020 | rnp->boost_kthread_status = RCU_KTHREAD_RUNNING; |
27f4d280 PM |
1021 | more2boost = rcu_boost(rnp); |
1022 | if (more2boost) | |
1023 | spincnt++; | |
1024 | else | |
1025 | spincnt = 0; | |
1026 | if (spincnt > 10) { | |
5d01bbd1 | 1027 | rnp->boost_kthread_status = RCU_KTHREAD_YIELDING; |
f7f7bac9 | 1028 | trace_rcu_utilization(TPS("End boost kthread@rcu_yield")); |
5d01bbd1 | 1029 | schedule_timeout_interruptible(2); |
f7f7bac9 | 1030 | trace_rcu_utilization(TPS("Start boost kthread@rcu_yield")); |
27f4d280 PM |
1031 | spincnt = 0; |
1032 | } | |
1033 | } | |
1217ed1b | 1034 | /* NOTREACHED */ |
f7f7bac9 | 1035 | trace_rcu_utilization(TPS("End boost kthread@notreached")); |
27f4d280 PM |
1036 | return 0; |
1037 | } | |
1038 | ||
1039 | /* | |
1040 | * Check to see if it is time to start boosting RCU readers that are | |
1041 | * blocking the current grace period, and, if so, tell the per-rcu_node | |
1042 | * kthread to start boosting them. If there is an expedited grace | |
1043 | * period in progress, it is always time to boost. | |
1044 | * | |
b065a853 PM |
1045 | * The caller must hold rnp->lock, which this function releases. |
1046 | * The ->boost_kthread_task is immortal, so we don't need to worry | |
1047 | * about it going away. | |
27f4d280 | 1048 | */ |
1217ed1b | 1049 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
615e41c6 | 1050 | __releases(rnp->lock) |
27f4d280 PM |
1051 | { |
1052 | struct task_struct *t; | |
1053 | ||
0ea1f2eb PM |
1054 | if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { |
1055 | rnp->n_balk_exp_gp_tasks++; | |
1217ed1b | 1056 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 | 1057 | return; |
0ea1f2eb | 1058 | } |
27f4d280 PM |
1059 | if (rnp->exp_tasks != NULL || |
1060 | (rnp->gp_tasks != NULL && | |
1061 | rnp->boost_tasks == NULL && | |
1062 | rnp->qsmask == 0 && | |
1063 | ULONG_CMP_GE(jiffies, rnp->boost_time))) { | |
1064 | if (rnp->exp_tasks == NULL) | |
1065 | rnp->boost_tasks = rnp->gp_tasks; | |
1217ed1b | 1066 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 | 1067 | t = rnp->boost_kthread_task; |
5d01bbd1 TG |
1068 | if (t) |
1069 | rcu_wake_cond(t, rnp->boost_kthread_status); | |
1217ed1b | 1070 | } else { |
0ea1f2eb | 1071 | rcu_initiate_boost_trace(rnp); |
1217ed1b PM |
1072 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1073 | } | |
27f4d280 PM |
1074 | } |
1075 | ||
a46e0899 PM |
1076 | /* |
1077 | * Wake up the per-CPU kthread to invoke RCU callbacks. | |
1078 | */ | |
1079 | static void invoke_rcu_callbacks_kthread(void) | |
1080 | { | |
1081 | unsigned long flags; | |
1082 | ||
1083 | local_irq_save(flags); | |
1084 | __this_cpu_write(rcu_cpu_has_work, 1); | |
1eb52121 | 1085 | if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && |
5d01bbd1 TG |
1086 | current != __this_cpu_read(rcu_cpu_kthread_task)) { |
1087 | rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), | |
1088 | __this_cpu_read(rcu_cpu_kthread_status)); | |
1089 | } | |
a46e0899 PM |
1090 | local_irq_restore(flags); |
1091 | } | |
1092 | ||
dff1672d PM |
1093 | /* |
1094 | * Is the current CPU running the RCU-callbacks kthread? | |
1095 | * Caller must have preemption disabled. | |
1096 | */ | |
1097 | static bool rcu_is_callbacks_kthread(void) | |
1098 | { | |
c9d4b0af | 1099 | return __this_cpu_read(rcu_cpu_kthread_task) == current; |
dff1672d PM |
1100 | } |
1101 | ||
27f4d280 PM |
1102 | #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) |
1103 | ||
1104 | /* | |
1105 | * Do priority-boost accounting for the start of a new grace period. | |
1106 | */ | |
1107 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) | |
1108 | { | |
1109 | rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; | |
1110 | } | |
1111 | ||
27f4d280 PM |
1112 | /* |
1113 | * Create an RCU-boost kthread for the specified node if one does not | |
1114 | * already exist. We only create this kthread for preemptible RCU. | |
1115 | * Returns zero if all is well, a negated errno otherwise. | |
1116 | */ | |
49fb4c62 | 1117 | static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp, |
0aa04b05 | 1118 | struct rcu_node *rnp) |
27f4d280 | 1119 | { |
5d01bbd1 | 1120 | int rnp_index = rnp - &rsp->node[0]; |
27f4d280 PM |
1121 | unsigned long flags; |
1122 | struct sched_param sp; | |
1123 | struct task_struct *t; | |
1124 | ||
e63c887c | 1125 | if (rcu_state_p != rsp) |
27f4d280 | 1126 | return 0; |
5d01bbd1 | 1127 | |
0aa04b05 | 1128 | if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0) |
5d01bbd1 TG |
1129 | return 0; |
1130 | ||
a46e0899 | 1131 | rsp->boost = 1; |
27f4d280 PM |
1132 | if (rnp->boost_kthread_task != NULL) |
1133 | return 0; | |
1134 | t = kthread_create(rcu_boost_kthread, (void *)rnp, | |
5b61b0ba | 1135 | "rcub/%d", rnp_index); |
27f4d280 PM |
1136 | if (IS_ERR(t)) |
1137 | return PTR_ERR(t); | |
1138 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
6303b9c8 | 1139 | smp_mb__after_unlock_lock(); |
27f4d280 PM |
1140 | rnp->boost_kthread_task = t; |
1141 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
21871d7e | 1142 | sp.sched_priority = kthread_prio; |
27f4d280 | 1143 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); |
9a432736 | 1144 | wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ |
27f4d280 PM |
1145 | return 0; |
1146 | } | |
1147 | ||
f8b7fc6b PM |
1148 | static void rcu_kthread_do_work(void) |
1149 | { | |
c9d4b0af CL |
1150 | rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data)); |
1151 | rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data)); | |
f8b7fc6b PM |
1152 | rcu_preempt_do_callbacks(); |
1153 | } | |
1154 | ||
62ab7072 | 1155 | static void rcu_cpu_kthread_setup(unsigned int cpu) |
f8b7fc6b | 1156 | { |
f8b7fc6b | 1157 | struct sched_param sp; |
f8b7fc6b | 1158 | |
21871d7e | 1159 | sp.sched_priority = kthread_prio; |
62ab7072 | 1160 | sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); |
f8b7fc6b PM |
1161 | } |
1162 | ||
62ab7072 | 1163 | static void rcu_cpu_kthread_park(unsigned int cpu) |
f8b7fc6b | 1164 | { |
62ab7072 | 1165 | per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; |
f8b7fc6b PM |
1166 | } |
1167 | ||
62ab7072 | 1168 | static int rcu_cpu_kthread_should_run(unsigned int cpu) |
f8b7fc6b | 1169 | { |
c9d4b0af | 1170 | return __this_cpu_read(rcu_cpu_has_work); |
f8b7fc6b PM |
1171 | } |
1172 | ||
1173 | /* | |
1174 | * Per-CPU kernel thread that invokes RCU callbacks. This replaces the | |
e0f23060 PM |
1175 | * RCU softirq used in flavors and configurations of RCU that do not |
1176 | * support RCU priority boosting. | |
f8b7fc6b | 1177 | */ |
62ab7072 | 1178 | static void rcu_cpu_kthread(unsigned int cpu) |
f8b7fc6b | 1179 | { |
c9d4b0af CL |
1180 | unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status); |
1181 | char work, *workp = this_cpu_ptr(&rcu_cpu_has_work); | |
62ab7072 | 1182 | int spincnt; |
f8b7fc6b | 1183 | |
62ab7072 | 1184 | for (spincnt = 0; spincnt < 10; spincnt++) { |
f7f7bac9 | 1185 | trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait")); |
f8b7fc6b | 1186 | local_bh_disable(); |
f8b7fc6b | 1187 | *statusp = RCU_KTHREAD_RUNNING; |
62ab7072 PM |
1188 | this_cpu_inc(rcu_cpu_kthread_loops); |
1189 | local_irq_disable(); | |
f8b7fc6b PM |
1190 | work = *workp; |
1191 | *workp = 0; | |
62ab7072 | 1192 | local_irq_enable(); |
f8b7fc6b PM |
1193 | if (work) |
1194 | rcu_kthread_do_work(); | |
1195 | local_bh_enable(); | |
62ab7072 | 1196 | if (*workp == 0) { |
f7f7bac9 | 1197 | trace_rcu_utilization(TPS("End CPU kthread@rcu_wait")); |
62ab7072 PM |
1198 | *statusp = RCU_KTHREAD_WAITING; |
1199 | return; | |
f8b7fc6b PM |
1200 | } |
1201 | } | |
62ab7072 | 1202 | *statusp = RCU_KTHREAD_YIELDING; |
f7f7bac9 | 1203 | trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield")); |
62ab7072 | 1204 | schedule_timeout_interruptible(2); |
f7f7bac9 | 1205 | trace_rcu_utilization(TPS("End CPU kthread@rcu_yield")); |
62ab7072 | 1206 | *statusp = RCU_KTHREAD_WAITING; |
f8b7fc6b PM |
1207 | } |
1208 | ||
1209 | /* | |
1210 | * Set the per-rcu_node kthread's affinity to cover all CPUs that are | |
1211 | * served by the rcu_node in question. The CPU hotplug lock is still | |
1212 | * held, so the value of rnp->qsmaskinit will be stable. | |
1213 | * | |
1214 | * We don't include outgoingcpu in the affinity set, use -1 if there is | |
1215 | * no outgoing CPU. If there are no CPUs left in the affinity set, | |
1216 | * this function allows the kthread to execute on any CPU. | |
1217 | */ | |
5d01bbd1 | 1218 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
f8b7fc6b | 1219 | { |
5d01bbd1 | 1220 | struct task_struct *t = rnp->boost_kthread_task; |
0aa04b05 | 1221 | unsigned long mask = rcu_rnp_online_cpus(rnp); |
f8b7fc6b PM |
1222 | cpumask_var_t cm; |
1223 | int cpu; | |
f8b7fc6b | 1224 | |
5d01bbd1 | 1225 | if (!t) |
f8b7fc6b | 1226 | return; |
5d01bbd1 | 1227 | if (!zalloc_cpumask_var(&cm, GFP_KERNEL)) |
f8b7fc6b | 1228 | return; |
f8b7fc6b PM |
1229 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) |
1230 | if ((mask & 0x1) && cpu != outgoingcpu) | |
1231 | cpumask_set_cpu(cpu, cm); | |
5d0b0249 | 1232 | if (cpumask_weight(cm) == 0) |
f8b7fc6b | 1233 | cpumask_setall(cm); |
5d01bbd1 | 1234 | set_cpus_allowed_ptr(t, cm); |
f8b7fc6b PM |
1235 | free_cpumask_var(cm); |
1236 | } | |
1237 | ||
62ab7072 PM |
1238 | static struct smp_hotplug_thread rcu_cpu_thread_spec = { |
1239 | .store = &rcu_cpu_kthread_task, | |
1240 | .thread_should_run = rcu_cpu_kthread_should_run, | |
1241 | .thread_fn = rcu_cpu_kthread, | |
1242 | .thread_comm = "rcuc/%u", | |
1243 | .setup = rcu_cpu_kthread_setup, | |
1244 | .park = rcu_cpu_kthread_park, | |
1245 | }; | |
f8b7fc6b PM |
1246 | |
1247 | /* | |
9386c0b7 | 1248 | * Spawn boost kthreads -- called as soon as the scheduler is running. |
f8b7fc6b | 1249 | */ |
9386c0b7 | 1250 | static void __init rcu_spawn_boost_kthreads(void) |
f8b7fc6b | 1251 | { |
f8b7fc6b | 1252 | struct rcu_node *rnp; |
5d01bbd1 | 1253 | int cpu; |
f8b7fc6b | 1254 | |
62ab7072 | 1255 | for_each_possible_cpu(cpu) |
f8b7fc6b | 1256 | per_cpu(rcu_cpu_has_work, cpu) = 0; |
62ab7072 | 1257 | BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec)); |
3e9f5c70 PM |
1258 | rcu_for_each_leaf_node(rcu_state_p, rnp) |
1259 | (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp); | |
f8b7fc6b | 1260 | } |
f8b7fc6b | 1261 | |
49fb4c62 | 1262 | static void rcu_prepare_kthreads(int cpu) |
f8b7fc6b | 1263 | { |
e534165b | 1264 | struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu); |
f8b7fc6b PM |
1265 | struct rcu_node *rnp = rdp->mynode; |
1266 | ||
1267 | /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ | |
62ab7072 | 1268 | if (rcu_scheduler_fully_active) |
e534165b | 1269 | (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp); |
f8b7fc6b PM |
1270 | } |
1271 | ||
27f4d280 PM |
1272 | #else /* #ifdef CONFIG_RCU_BOOST */ |
1273 | ||
1217ed1b | 1274 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
615e41c6 | 1275 | __releases(rnp->lock) |
27f4d280 | 1276 | { |
1217ed1b | 1277 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 PM |
1278 | } |
1279 | ||
a46e0899 | 1280 | static void invoke_rcu_callbacks_kthread(void) |
27f4d280 | 1281 | { |
a46e0899 | 1282 | WARN_ON_ONCE(1); |
27f4d280 PM |
1283 | } |
1284 | ||
dff1672d PM |
1285 | static bool rcu_is_callbacks_kthread(void) |
1286 | { | |
1287 | return false; | |
1288 | } | |
1289 | ||
27f4d280 PM |
1290 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) |
1291 | { | |
1292 | } | |
1293 | ||
5d01bbd1 | 1294 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
f8b7fc6b PM |
1295 | { |
1296 | } | |
1297 | ||
9386c0b7 | 1298 | static void __init rcu_spawn_boost_kthreads(void) |
b0d30417 | 1299 | { |
b0d30417 | 1300 | } |
b0d30417 | 1301 | |
49fb4c62 | 1302 | static void rcu_prepare_kthreads(int cpu) |
f8b7fc6b PM |
1303 | { |
1304 | } | |
1305 | ||
27f4d280 PM |
1306 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
1307 | ||
8bd93a2c PM |
1308 | #if !defined(CONFIG_RCU_FAST_NO_HZ) |
1309 | ||
1310 | /* | |
1311 | * Check to see if any future RCU-related work will need to be done | |
1312 | * by the current CPU, even if none need be done immediately, returning | |
1313 | * 1 if so. This function is part of the RCU implementation; it is -not- | |
1314 | * an exported member of the RCU API. | |
1315 | * | |
7cb92499 PM |
1316 | * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs |
1317 | * any flavor of RCU. | |
8bd93a2c | 1318 | */ |
c1ad348b | 1319 | int rcu_needs_cpu(u64 basemono, u64 *nextevt) |
8bd93a2c | 1320 | { |
c1ad348b | 1321 | *nextevt = KTIME_MAX; |
3382adbc PM |
1322 | return IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) |
1323 | ? 0 : rcu_cpu_has_callbacks(NULL); | |
7cb92499 PM |
1324 | } |
1325 | ||
1326 | /* | |
1327 | * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up | |
1328 | * after it. | |
1329 | */ | |
8fa7845d | 1330 | static void rcu_cleanup_after_idle(void) |
7cb92499 PM |
1331 | { |
1332 | } | |
1333 | ||
aea1b35e | 1334 | /* |
a858af28 | 1335 | * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n, |
aea1b35e PM |
1336 | * is nothing. |
1337 | */ | |
198bbf81 | 1338 | static void rcu_prepare_for_idle(void) |
aea1b35e PM |
1339 | { |
1340 | } | |
1341 | ||
c57afe80 PM |
1342 | /* |
1343 | * Don't bother keeping a running count of the number of RCU callbacks | |
1344 | * posted because CONFIG_RCU_FAST_NO_HZ=n. | |
1345 | */ | |
1346 | static void rcu_idle_count_callbacks_posted(void) | |
1347 | { | |
1348 | } | |
1349 | ||
8bd93a2c PM |
1350 | #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
1351 | ||
f23f7fa1 PM |
1352 | /* |
1353 | * This code is invoked when a CPU goes idle, at which point we want | |
1354 | * to have the CPU do everything required for RCU so that it can enter | |
1355 | * the energy-efficient dyntick-idle mode. This is handled by a | |
1356 | * state machine implemented by rcu_prepare_for_idle() below. | |
1357 | * | |
1358 | * The following three proprocessor symbols control this state machine: | |
1359 | * | |
f23f7fa1 PM |
1360 | * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted |
1361 | * to sleep in dyntick-idle mode with RCU callbacks pending. This | |
1362 | * is sized to be roughly one RCU grace period. Those energy-efficiency | |
1363 | * benchmarkers who might otherwise be tempted to set this to a large | |
1364 | * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your | |
1365 | * system. And if you are -that- concerned about energy efficiency, | |
1366 | * just power the system down and be done with it! | |
778d250a PM |
1367 | * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is |
1368 | * permitted to sleep in dyntick-idle mode with only lazy RCU | |
1369 | * callbacks pending. Setting this too high can OOM your system. | |
f23f7fa1 PM |
1370 | * |
1371 | * The values below work well in practice. If future workloads require | |
1372 | * adjustment, they can be converted into kernel config parameters, though | |
1373 | * making the state machine smarter might be a better option. | |
1374 | */ | |
e84c48ae | 1375 | #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */ |
778d250a | 1376 | #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ |
f23f7fa1 | 1377 | |
5e44ce35 PM |
1378 | static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY; |
1379 | module_param(rcu_idle_gp_delay, int, 0644); | |
1380 | static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY; | |
1381 | module_param(rcu_idle_lazy_gp_delay, int, 0644); | |
486e2593 | 1382 | |
486e2593 | 1383 | /* |
c229828c PM |
1384 | * Try to advance callbacks for all flavors of RCU on the current CPU, but |
1385 | * only if it has been awhile since the last time we did so. Afterwards, | |
1386 | * if there are any callbacks ready for immediate invocation, return true. | |
486e2593 | 1387 | */ |
f1f399d1 | 1388 | static bool __maybe_unused rcu_try_advance_all_cbs(void) |
486e2593 | 1389 | { |
c0f4dfd4 PM |
1390 | bool cbs_ready = false; |
1391 | struct rcu_data *rdp; | |
c229828c | 1392 | struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
c0f4dfd4 PM |
1393 | struct rcu_node *rnp; |
1394 | struct rcu_state *rsp; | |
486e2593 | 1395 | |
c229828c PM |
1396 | /* Exit early if we advanced recently. */ |
1397 | if (jiffies == rdtp->last_advance_all) | |
d0bc90fd | 1398 | return false; |
c229828c PM |
1399 | rdtp->last_advance_all = jiffies; |
1400 | ||
c0f4dfd4 PM |
1401 | for_each_rcu_flavor(rsp) { |
1402 | rdp = this_cpu_ptr(rsp->rda); | |
1403 | rnp = rdp->mynode; | |
486e2593 | 1404 | |
c0f4dfd4 PM |
1405 | /* |
1406 | * Don't bother checking unless a grace period has | |
1407 | * completed since we last checked and there are | |
1408 | * callbacks not yet ready to invoke. | |
1409 | */ | |
e3663b10 | 1410 | if ((rdp->completed != rnp->completed || |
7d0ae808 | 1411 | unlikely(READ_ONCE(rdp->gpwrap))) && |
c0f4dfd4 | 1412 | rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL]) |
470716fc | 1413 | note_gp_changes(rsp, rdp); |
486e2593 | 1414 | |
c0f4dfd4 PM |
1415 | if (cpu_has_callbacks_ready_to_invoke(rdp)) |
1416 | cbs_ready = true; | |
1417 | } | |
1418 | return cbs_ready; | |
486e2593 PM |
1419 | } |
1420 | ||
aa9b1630 | 1421 | /* |
c0f4dfd4 PM |
1422 | * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready |
1423 | * to invoke. If the CPU has callbacks, try to advance them. Tell the | |
1424 | * caller to set the timeout based on whether or not there are non-lazy | |
1425 | * callbacks. | |
aa9b1630 | 1426 | * |
c0f4dfd4 | 1427 | * The caller must have disabled interrupts. |
aa9b1630 | 1428 | */ |
c1ad348b | 1429 | int rcu_needs_cpu(u64 basemono, u64 *nextevt) |
aa9b1630 | 1430 | { |
aa6da514 | 1431 | struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
c1ad348b | 1432 | unsigned long dj; |
aa9b1630 | 1433 | |
3382adbc | 1434 | if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL)) { |
43224b96 | 1435 | *nextevt = KTIME_MAX; |
3382adbc PM |
1436 | return 0; |
1437 | } | |
1438 | ||
c0f4dfd4 PM |
1439 | /* Snapshot to detect later posting of non-lazy callback. */ |
1440 | rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; | |
1441 | ||
aa9b1630 | 1442 | /* If no callbacks, RCU doesn't need the CPU. */ |
aa6da514 | 1443 | if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) { |
c1ad348b | 1444 | *nextevt = KTIME_MAX; |
aa9b1630 PM |
1445 | return 0; |
1446 | } | |
c0f4dfd4 PM |
1447 | |
1448 | /* Attempt to advance callbacks. */ | |
1449 | if (rcu_try_advance_all_cbs()) { | |
1450 | /* Some ready to invoke, so initiate later invocation. */ | |
1451 | invoke_rcu_core(); | |
aa9b1630 PM |
1452 | return 1; |
1453 | } | |
c0f4dfd4 PM |
1454 | rdtp->last_accelerate = jiffies; |
1455 | ||
1456 | /* Request timer delay depending on laziness, and round. */ | |
6faf7283 | 1457 | if (!rdtp->all_lazy) { |
c1ad348b | 1458 | dj = round_up(rcu_idle_gp_delay + jiffies, |
c0f4dfd4 | 1459 | rcu_idle_gp_delay) - jiffies; |
e84c48ae | 1460 | } else { |
c1ad348b | 1461 | dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies; |
e84c48ae | 1462 | } |
c1ad348b | 1463 | *nextevt = basemono + dj * TICK_NSEC; |
aa9b1630 PM |
1464 | return 0; |
1465 | } | |
1466 | ||
21e52e15 | 1467 | /* |
c0f4dfd4 PM |
1468 | * Prepare a CPU for idle from an RCU perspective. The first major task |
1469 | * is to sense whether nohz mode has been enabled or disabled via sysfs. | |
1470 | * The second major task is to check to see if a non-lazy callback has | |
1471 | * arrived at a CPU that previously had only lazy callbacks. The third | |
1472 | * major task is to accelerate (that is, assign grace-period numbers to) | |
1473 | * any recently arrived callbacks. | |
aea1b35e PM |
1474 | * |
1475 | * The caller must have disabled interrupts. | |
8bd93a2c | 1476 | */ |
198bbf81 | 1477 | static void rcu_prepare_for_idle(void) |
8bd93a2c | 1478 | { |
48a7639c | 1479 | bool needwake; |
c0f4dfd4 | 1480 | struct rcu_data *rdp; |
198bbf81 | 1481 | struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
c0f4dfd4 PM |
1482 | struct rcu_node *rnp; |
1483 | struct rcu_state *rsp; | |
9d2ad243 PM |
1484 | int tne; |
1485 | ||
3382adbc PM |
1486 | if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL)) |
1487 | return; | |
1488 | ||
9d2ad243 | 1489 | /* Handle nohz enablement switches conservatively. */ |
7d0ae808 | 1490 | tne = READ_ONCE(tick_nohz_active); |
9d2ad243 | 1491 | if (tne != rdtp->tick_nohz_enabled_snap) { |
aa6da514 | 1492 | if (rcu_cpu_has_callbacks(NULL)) |
9d2ad243 PM |
1493 | invoke_rcu_core(); /* force nohz to see update. */ |
1494 | rdtp->tick_nohz_enabled_snap = tne; | |
1495 | return; | |
1496 | } | |
1497 | if (!tne) | |
1498 | return; | |
f511fc62 | 1499 | |
c0f4dfd4 | 1500 | /* If this is a no-CBs CPU, no callbacks, just return. */ |
198bbf81 | 1501 | if (rcu_is_nocb_cpu(smp_processor_id())) |
9a0c6fef | 1502 | return; |
9a0c6fef | 1503 | |
c57afe80 | 1504 | /* |
c0f4dfd4 PM |
1505 | * If a non-lazy callback arrived at a CPU having only lazy |
1506 | * callbacks, invoke RCU core for the side-effect of recalculating | |
1507 | * idle duration on re-entry to idle. | |
c57afe80 | 1508 | */ |
c0f4dfd4 PM |
1509 | if (rdtp->all_lazy && |
1510 | rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) { | |
c337f8f5 PM |
1511 | rdtp->all_lazy = false; |
1512 | rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; | |
c0f4dfd4 | 1513 | invoke_rcu_core(); |
c57afe80 PM |
1514 | return; |
1515 | } | |
c57afe80 | 1516 | |
3084f2f8 | 1517 | /* |
c0f4dfd4 PM |
1518 | * If we have not yet accelerated this jiffy, accelerate all |
1519 | * callbacks on this CPU. | |
3084f2f8 | 1520 | */ |
c0f4dfd4 | 1521 | if (rdtp->last_accelerate == jiffies) |
aea1b35e | 1522 | return; |
c0f4dfd4 PM |
1523 | rdtp->last_accelerate = jiffies; |
1524 | for_each_rcu_flavor(rsp) { | |
198bbf81 | 1525 | rdp = this_cpu_ptr(rsp->rda); |
c0f4dfd4 PM |
1526 | if (!*rdp->nxttail[RCU_DONE_TAIL]) |
1527 | continue; | |
1528 | rnp = rdp->mynode; | |
1529 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ | |
6303b9c8 | 1530 | smp_mb__after_unlock_lock(); |
48a7639c | 1531 | needwake = rcu_accelerate_cbs(rsp, rnp, rdp); |
c0f4dfd4 | 1532 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
48a7639c PM |
1533 | if (needwake) |
1534 | rcu_gp_kthread_wake(rsp); | |
77e38ed3 | 1535 | } |
c0f4dfd4 | 1536 | } |
3084f2f8 | 1537 | |
c0f4dfd4 PM |
1538 | /* |
1539 | * Clean up for exit from idle. Attempt to advance callbacks based on | |
1540 | * any grace periods that elapsed while the CPU was idle, and if any | |
1541 | * callbacks are now ready to invoke, initiate invocation. | |
1542 | */ | |
8fa7845d | 1543 | static void rcu_cleanup_after_idle(void) |
c0f4dfd4 | 1544 | { |
3382adbc PM |
1545 | if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) || |
1546 | rcu_is_nocb_cpu(smp_processor_id())) | |
aea1b35e | 1547 | return; |
7a497c96 PM |
1548 | if (rcu_try_advance_all_cbs()) |
1549 | invoke_rcu_core(); | |
8bd93a2c PM |
1550 | } |
1551 | ||
c57afe80 | 1552 | /* |
98248a0e PM |
1553 | * Keep a running count of the number of non-lazy callbacks posted |
1554 | * on this CPU. This running counter (which is never decremented) allows | |
1555 | * rcu_prepare_for_idle() to detect when something out of the idle loop | |
1556 | * posts a callback, even if an equal number of callbacks are invoked. | |
1557 | * Of course, callbacks should only be posted from within a trace event | |
1558 | * designed to be called from idle or from within RCU_NONIDLE(). | |
c57afe80 PM |
1559 | */ |
1560 | static void rcu_idle_count_callbacks_posted(void) | |
1561 | { | |
5955f7ee | 1562 | __this_cpu_add(rcu_dynticks.nonlazy_posted, 1); |
c57afe80 PM |
1563 | } |
1564 | ||
b626c1b6 PM |
1565 | /* |
1566 | * Data for flushing lazy RCU callbacks at OOM time. | |
1567 | */ | |
1568 | static atomic_t oom_callback_count; | |
1569 | static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq); | |
1570 | ||
1571 | /* | |
1572 | * RCU OOM callback -- decrement the outstanding count and deliver the | |
1573 | * wake-up if we are the last one. | |
1574 | */ | |
1575 | static void rcu_oom_callback(struct rcu_head *rhp) | |
1576 | { | |
1577 | if (atomic_dec_and_test(&oom_callback_count)) | |
1578 | wake_up(&oom_callback_wq); | |
1579 | } | |
1580 | ||
1581 | /* | |
1582 | * Post an rcu_oom_notify callback on the current CPU if it has at | |
1583 | * least one lazy callback. This will unnecessarily post callbacks | |
1584 | * to CPUs that already have a non-lazy callback at the end of their | |
1585 | * callback list, but this is an infrequent operation, so accept some | |
1586 | * extra overhead to keep things simple. | |
1587 | */ | |
1588 | static void rcu_oom_notify_cpu(void *unused) | |
1589 | { | |
1590 | struct rcu_state *rsp; | |
1591 | struct rcu_data *rdp; | |
1592 | ||
1593 | for_each_rcu_flavor(rsp) { | |
fa07a58f | 1594 | rdp = raw_cpu_ptr(rsp->rda); |
b626c1b6 PM |
1595 | if (rdp->qlen_lazy != 0) { |
1596 | atomic_inc(&oom_callback_count); | |
1597 | rsp->call(&rdp->oom_head, rcu_oom_callback); | |
1598 | } | |
1599 | } | |
1600 | } | |
1601 | ||
1602 | /* | |
1603 | * If low on memory, ensure that each CPU has a non-lazy callback. | |
1604 | * This will wake up CPUs that have only lazy callbacks, in turn | |
1605 | * ensuring that they free up the corresponding memory in a timely manner. | |
1606 | * Because an uncertain amount of memory will be freed in some uncertain | |
1607 | * timeframe, we do not claim to have freed anything. | |
1608 | */ | |
1609 | static int rcu_oom_notify(struct notifier_block *self, | |
1610 | unsigned long notused, void *nfreed) | |
1611 | { | |
1612 | int cpu; | |
1613 | ||
1614 | /* Wait for callbacks from earlier instance to complete. */ | |
1615 | wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0); | |
78e4bc34 | 1616 | smp_mb(); /* Ensure callback reuse happens after callback invocation. */ |
b626c1b6 PM |
1617 | |
1618 | /* | |
1619 | * Prevent premature wakeup: ensure that all increments happen | |
1620 | * before there is a chance of the counter reaching zero. | |
1621 | */ | |
1622 | atomic_set(&oom_callback_count, 1); | |
1623 | ||
b626c1b6 PM |
1624 | for_each_online_cpu(cpu) { |
1625 | smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1); | |
bde6c3aa | 1626 | cond_resched_rcu_qs(); |
b626c1b6 | 1627 | } |
b626c1b6 PM |
1628 | |
1629 | /* Unconditionally decrement: no need to wake ourselves up. */ | |
1630 | atomic_dec(&oom_callback_count); | |
1631 | ||
1632 | return NOTIFY_OK; | |
1633 | } | |
1634 | ||
1635 | static struct notifier_block rcu_oom_nb = { | |
1636 | .notifier_call = rcu_oom_notify | |
1637 | }; | |
1638 | ||
1639 | static int __init rcu_register_oom_notifier(void) | |
1640 | { | |
1641 | register_oom_notifier(&rcu_oom_nb); | |
1642 | return 0; | |
1643 | } | |
1644 | early_initcall(rcu_register_oom_notifier); | |
1645 | ||
8bd93a2c | 1646 | #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
a858af28 | 1647 | |
a858af28 PM |
1648 | #ifdef CONFIG_RCU_FAST_NO_HZ |
1649 | ||
1650 | static void print_cpu_stall_fast_no_hz(char *cp, int cpu) | |
1651 | { | |
5955f7ee | 1652 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
c0f4dfd4 | 1653 | unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap; |
a858af28 | 1654 | |
c0f4dfd4 PM |
1655 | sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c", |
1656 | rdtp->last_accelerate & 0xffff, jiffies & 0xffff, | |
1657 | ulong2long(nlpd), | |
1658 | rdtp->all_lazy ? 'L' : '.', | |
1659 | rdtp->tick_nohz_enabled_snap ? '.' : 'D'); | |
a858af28 PM |
1660 | } |
1661 | ||
1662 | #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ | |
1663 | ||
1664 | static void print_cpu_stall_fast_no_hz(char *cp, int cpu) | |
1665 | { | |
1c17e4d4 | 1666 | *cp = '\0'; |
a858af28 PM |
1667 | } |
1668 | ||
1669 | #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ | |
1670 | ||
1671 | /* Initiate the stall-info list. */ | |
1672 | static void print_cpu_stall_info_begin(void) | |
1673 | { | |
efc151c3 | 1674 | pr_cont("\n"); |
a858af28 PM |
1675 | } |
1676 | ||
1677 | /* | |
1678 | * Print out diagnostic information for the specified stalled CPU. | |
1679 | * | |
1680 | * If the specified CPU is aware of the current RCU grace period | |
1681 | * (flavor specified by rsp), then print the number of scheduling | |
1682 | * clock interrupts the CPU has taken during the time that it has | |
1683 | * been aware. Otherwise, print the number of RCU grace periods | |
1684 | * that this CPU is ignorant of, for example, "1" if the CPU was | |
1685 | * aware of the previous grace period. | |
1686 | * | |
1687 | * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. | |
1688 | */ | |
1689 | static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) | |
1690 | { | |
1691 | char fast_no_hz[72]; | |
1692 | struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); | |
1693 | struct rcu_dynticks *rdtp = rdp->dynticks; | |
1694 | char *ticks_title; | |
1695 | unsigned long ticks_value; | |
1696 | ||
1697 | if (rsp->gpnum == rdp->gpnum) { | |
1698 | ticks_title = "ticks this GP"; | |
1699 | ticks_value = rdp->ticks_this_gp; | |
1700 | } else { | |
1701 | ticks_title = "GPs behind"; | |
1702 | ticks_value = rsp->gpnum - rdp->gpnum; | |
1703 | } | |
1704 | print_cpu_stall_fast_no_hz(fast_no_hz, cpu); | |
fc908ed3 | 1705 | pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n", |
a858af28 PM |
1706 | cpu, ticks_value, ticks_title, |
1707 | atomic_read(&rdtp->dynticks) & 0xfff, | |
1708 | rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting, | |
6231069b | 1709 | rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), |
7d0ae808 | 1710 | READ_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart, |
a858af28 PM |
1711 | fast_no_hz); |
1712 | } | |
1713 | ||
1714 | /* Terminate the stall-info list. */ | |
1715 | static void print_cpu_stall_info_end(void) | |
1716 | { | |
efc151c3 | 1717 | pr_err("\t"); |
a858af28 PM |
1718 | } |
1719 | ||
1720 | /* Zero ->ticks_this_gp for all flavors of RCU. */ | |
1721 | static void zero_cpu_stall_ticks(struct rcu_data *rdp) | |
1722 | { | |
1723 | rdp->ticks_this_gp = 0; | |
6231069b | 1724 | rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id()); |
a858af28 PM |
1725 | } |
1726 | ||
1727 | /* Increment ->ticks_this_gp for all flavors of RCU. */ | |
1728 | static void increment_cpu_stall_ticks(void) | |
1729 | { | |
115f7a7c PM |
1730 | struct rcu_state *rsp; |
1731 | ||
1732 | for_each_rcu_flavor(rsp) | |
fa07a58f | 1733 | raw_cpu_inc(rsp->rda->ticks_this_gp); |
a858af28 PM |
1734 | } |
1735 | ||
3fbfbf7a PM |
1736 | #ifdef CONFIG_RCU_NOCB_CPU |
1737 | ||
1738 | /* | |
1739 | * Offload callback processing from the boot-time-specified set of CPUs | |
1740 | * specified by rcu_nocb_mask. For each CPU in the set, there is a | |
1741 | * kthread created that pulls the callbacks from the corresponding CPU, | |
1742 | * waits for a grace period to elapse, and invokes the callbacks. | |
1743 | * The no-CBs CPUs do a wake_up() on their kthread when they insert | |
1744 | * a callback into any empty list, unless the rcu_nocb_poll boot parameter | |
1745 | * has been specified, in which case each kthread actively polls its | |
1746 | * CPU. (Which isn't so great for energy efficiency, but which does | |
1747 | * reduce RCU's overhead on that CPU.) | |
1748 | * | |
1749 | * This is intended to be used in conjunction with Frederic Weisbecker's | |
1750 | * adaptive-idle work, which would seriously reduce OS jitter on CPUs | |
1751 | * running CPU-bound user-mode computations. | |
1752 | * | |
1753 | * Offloading of callback processing could also in theory be used as | |
1754 | * an energy-efficiency measure because CPUs with no RCU callbacks | |
1755 | * queued are more aggressive about entering dyntick-idle mode. | |
1756 | */ | |
1757 | ||
1758 | ||
1759 | /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */ | |
1760 | static int __init rcu_nocb_setup(char *str) | |
1761 | { | |
1762 | alloc_bootmem_cpumask_var(&rcu_nocb_mask); | |
1763 | have_rcu_nocb_mask = true; | |
1764 | cpulist_parse(str, rcu_nocb_mask); | |
1765 | return 1; | |
1766 | } | |
1767 | __setup("rcu_nocbs=", rcu_nocb_setup); | |
1768 | ||
1b0048a4 PG |
1769 | static int __init parse_rcu_nocb_poll(char *arg) |
1770 | { | |
1771 | rcu_nocb_poll = 1; | |
1772 | return 0; | |
1773 | } | |
1774 | early_param("rcu_nocb_poll", parse_rcu_nocb_poll); | |
1775 | ||
dae6e64d | 1776 | /* |
0446be48 PM |
1777 | * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended |
1778 | * grace period. | |
dae6e64d | 1779 | */ |
0446be48 | 1780 | static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) |
dae6e64d | 1781 | { |
0446be48 | 1782 | wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]); |
dae6e64d PM |
1783 | } |
1784 | ||
1785 | /* | |
8b425aa8 | 1786 | * Set the root rcu_node structure's ->need_future_gp field |
dae6e64d PM |
1787 | * based on the sum of those of all rcu_node structures. This does |
1788 | * double-count the root rcu_node structure's requests, but this | |
1789 | * is necessary to handle the possibility of a rcu_nocb_kthread() | |
1790 | * having awakened during the time that the rcu_node structures | |
1791 | * were being updated for the end of the previous grace period. | |
34ed6246 | 1792 | */ |
dae6e64d PM |
1793 | static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) |
1794 | { | |
8b425aa8 | 1795 | rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq; |
dae6e64d PM |
1796 | } |
1797 | ||
1798 | static void rcu_init_one_nocb(struct rcu_node *rnp) | |
34ed6246 | 1799 | { |
dae6e64d PM |
1800 | init_waitqueue_head(&rnp->nocb_gp_wq[0]); |
1801 | init_waitqueue_head(&rnp->nocb_gp_wq[1]); | |
34ed6246 PM |
1802 | } |
1803 | ||
2f33b512 | 1804 | #ifndef CONFIG_RCU_NOCB_CPU_ALL |
24342c96 | 1805 | /* Is the specified CPU a no-CBs CPU? */ |
d1e43fa5 | 1806 | bool rcu_is_nocb_cpu(int cpu) |
3fbfbf7a PM |
1807 | { |
1808 | if (have_rcu_nocb_mask) | |
1809 | return cpumask_test_cpu(cpu, rcu_nocb_mask); | |
1810 | return false; | |
1811 | } | |
2f33b512 | 1812 | #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ |
3fbfbf7a | 1813 | |
fbce7497 PM |
1814 | /* |
1815 | * Kick the leader kthread for this NOCB group. | |
1816 | */ | |
1817 | static void wake_nocb_leader(struct rcu_data *rdp, bool force) | |
1818 | { | |
1819 | struct rcu_data *rdp_leader = rdp->nocb_leader; | |
1820 | ||
7d0ae808 | 1821 | if (!READ_ONCE(rdp_leader->nocb_kthread)) |
fbce7497 | 1822 | return; |
7d0ae808 | 1823 | if (READ_ONCE(rdp_leader->nocb_leader_sleep) || force) { |
39953dfd | 1824 | /* Prior smp_mb__after_atomic() orders against prior enqueue. */ |
7d0ae808 | 1825 | WRITE_ONCE(rdp_leader->nocb_leader_sleep, false); |
fbce7497 PM |
1826 | wake_up(&rdp_leader->nocb_wq); |
1827 | } | |
1828 | } | |
1829 | ||
d7e29933 PM |
1830 | /* |
1831 | * Does the specified CPU need an RCU callback for the specified flavor | |
1832 | * of rcu_barrier()? | |
1833 | */ | |
1834 | static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) | |
1835 | { | |
1836 | struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); | |
41050a00 PM |
1837 | unsigned long ret; |
1838 | #ifdef CONFIG_PROVE_RCU | |
d7e29933 | 1839 | struct rcu_head *rhp; |
41050a00 | 1840 | #endif /* #ifdef CONFIG_PROVE_RCU */ |
d7e29933 | 1841 | |
41050a00 PM |
1842 | /* |
1843 | * Check count of all no-CBs callbacks awaiting invocation. | |
1844 | * There needs to be a barrier before this function is called, | |
1845 | * but associated with a prior determination that no more | |
1846 | * callbacks would be posted. In the worst case, the first | |
1847 | * barrier in _rcu_barrier() suffices (but the caller cannot | |
1848 | * necessarily rely on this, not a substitute for the caller | |
1849 | * getting the concurrency design right!). There must also be | |
1850 | * a barrier between the following load an posting of a callback | |
1851 | * (if a callback is in fact needed). This is associated with an | |
1852 | * atomic_inc() in the caller. | |
1853 | */ | |
1854 | ret = atomic_long_read(&rdp->nocb_q_count); | |
d7e29933 | 1855 | |
41050a00 | 1856 | #ifdef CONFIG_PROVE_RCU |
7d0ae808 | 1857 | rhp = READ_ONCE(rdp->nocb_head); |
d7e29933 | 1858 | if (!rhp) |
7d0ae808 | 1859 | rhp = READ_ONCE(rdp->nocb_gp_head); |
d7e29933 | 1860 | if (!rhp) |
7d0ae808 | 1861 | rhp = READ_ONCE(rdp->nocb_follower_head); |
d7e29933 PM |
1862 | |
1863 | /* Having no rcuo kthread but CBs after scheduler starts is bad! */ | |
7d0ae808 | 1864 | if (!READ_ONCE(rdp->nocb_kthread) && rhp && |
59f792d1 | 1865 | rcu_scheduler_fully_active) { |
d7e29933 PM |
1866 | /* RCU callback enqueued before CPU first came online??? */ |
1867 | pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n", | |
1868 | cpu, rhp->func); | |
1869 | WARN_ON_ONCE(1); | |
1870 | } | |
41050a00 | 1871 | #endif /* #ifdef CONFIG_PROVE_RCU */ |
d7e29933 | 1872 | |
41050a00 | 1873 | return !!ret; |
d7e29933 PM |
1874 | } |
1875 | ||
3fbfbf7a PM |
1876 | /* |
1877 | * Enqueue the specified string of rcu_head structures onto the specified | |
1878 | * CPU's no-CBs lists. The CPU is specified by rdp, the head of the | |
1879 | * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy | |
1880 | * counts are supplied by rhcount and rhcount_lazy. | |
1881 | * | |
1882 | * If warranted, also wake up the kthread servicing this CPUs queues. | |
1883 | */ | |
1884 | static void __call_rcu_nocb_enqueue(struct rcu_data *rdp, | |
1885 | struct rcu_head *rhp, | |
1886 | struct rcu_head **rhtp, | |
96d3fd0d PM |
1887 | int rhcount, int rhcount_lazy, |
1888 | unsigned long flags) | |
3fbfbf7a PM |
1889 | { |
1890 | int len; | |
1891 | struct rcu_head **old_rhpp; | |
1892 | struct task_struct *t; | |
1893 | ||
1894 | /* Enqueue the callback on the nocb list and update counts. */ | |
41050a00 PM |
1895 | atomic_long_add(rhcount, &rdp->nocb_q_count); |
1896 | /* rcu_barrier() relies on ->nocb_q_count add before xchg. */ | |
3fbfbf7a | 1897 | old_rhpp = xchg(&rdp->nocb_tail, rhtp); |
7d0ae808 | 1898 | WRITE_ONCE(*old_rhpp, rhp); |
3fbfbf7a | 1899 | atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy); |
39953dfd | 1900 | smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */ |
3fbfbf7a PM |
1901 | |
1902 | /* If we are not being polled and there is a kthread, awaken it ... */ | |
7d0ae808 | 1903 | t = READ_ONCE(rdp->nocb_kthread); |
25e03a74 | 1904 | if (rcu_nocb_poll || !t) { |
9261dd0d PM |
1905 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
1906 | TPS("WakeNotPoll")); | |
3fbfbf7a | 1907 | return; |
9261dd0d | 1908 | } |
3fbfbf7a PM |
1909 | len = atomic_long_read(&rdp->nocb_q_count); |
1910 | if (old_rhpp == &rdp->nocb_head) { | |
96d3fd0d | 1911 | if (!irqs_disabled_flags(flags)) { |
fbce7497 PM |
1912 | /* ... if queue was empty ... */ |
1913 | wake_nocb_leader(rdp, false); | |
96d3fd0d PM |
1914 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
1915 | TPS("WakeEmpty")); | |
1916 | } else { | |
9fdd3bc9 | 1917 | rdp->nocb_defer_wakeup = RCU_NOGP_WAKE; |
96d3fd0d PM |
1918 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
1919 | TPS("WakeEmptyIsDeferred")); | |
1920 | } | |
3fbfbf7a PM |
1921 | rdp->qlen_last_fqs_check = 0; |
1922 | } else if (len > rdp->qlen_last_fqs_check + qhimark) { | |
fbce7497 | 1923 | /* ... or if many callbacks queued. */ |
9fdd3bc9 PM |
1924 | if (!irqs_disabled_flags(flags)) { |
1925 | wake_nocb_leader(rdp, true); | |
1926 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, | |
1927 | TPS("WakeOvf")); | |
1928 | } else { | |
1929 | rdp->nocb_defer_wakeup = RCU_NOGP_WAKE_FORCE; | |
1930 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, | |
1931 | TPS("WakeOvfIsDeferred")); | |
1932 | } | |
3fbfbf7a | 1933 | rdp->qlen_last_fqs_check = LONG_MAX / 2; |
9261dd0d PM |
1934 | } else { |
1935 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot")); | |
3fbfbf7a PM |
1936 | } |
1937 | return; | |
1938 | } | |
1939 | ||
1940 | /* | |
1941 | * This is a helper for __call_rcu(), which invokes this when the normal | |
1942 | * callback queue is inoperable. If this is not a no-CBs CPU, this | |
1943 | * function returns failure back to __call_rcu(), which can complain | |
1944 | * appropriately. | |
1945 | * | |
1946 | * Otherwise, this function queues the callback where the corresponding | |
1947 | * "rcuo" kthread can find it. | |
1948 | */ | |
1949 | static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, | |
96d3fd0d | 1950 | bool lazy, unsigned long flags) |
3fbfbf7a PM |
1951 | { |
1952 | ||
d1e43fa5 | 1953 | if (!rcu_is_nocb_cpu(rdp->cpu)) |
c271d3a9 | 1954 | return false; |
96d3fd0d | 1955 | __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags); |
21e7a608 PM |
1956 | if (__is_kfree_rcu_offset((unsigned long)rhp->func)) |
1957 | trace_rcu_kfree_callback(rdp->rsp->name, rhp, | |
1958 | (unsigned long)rhp->func, | |
756cbf6b PM |
1959 | -atomic_long_read(&rdp->nocb_q_count_lazy), |
1960 | -atomic_long_read(&rdp->nocb_q_count)); | |
21e7a608 PM |
1961 | else |
1962 | trace_rcu_callback(rdp->rsp->name, rhp, | |
756cbf6b PM |
1963 | -atomic_long_read(&rdp->nocb_q_count_lazy), |
1964 | -atomic_long_read(&rdp->nocb_q_count)); | |
1772947b PM |
1965 | |
1966 | /* | |
1967 | * If called from an extended quiescent state with interrupts | |
1968 | * disabled, invoke the RCU core in order to allow the idle-entry | |
1969 | * deferred-wakeup check to function. | |
1970 | */ | |
1971 | if (irqs_disabled_flags(flags) && | |
1972 | !rcu_is_watching() && | |
1973 | cpu_online(smp_processor_id())) | |
1974 | invoke_rcu_core(); | |
1975 | ||
c271d3a9 | 1976 | return true; |
3fbfbf7a PM |
1977 | } |
1978 | ||
1979 | /* | |
1980 | * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is | |
1981 | * not a no-CBs CPU. | |
1982 | */ | |
1983 | static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, | |
96d3fd0d PM |
1984 | struct rcu_data *rdp, |
1985 | unsigned long flags) | |
3fbfbf7a PM |
1986 | { |
1987 | long ql = rsp->qlen; | |
1988 | long qll = rsp->qlen_lazy; | |
1989 | ||
1990 | /* If this is not a no-CBs CPU, tell the caller to do it the old way. */ | |
d1e43fa5 | 1991 | if (!rcu_is_nocb_cpu(smp_processor_id())) |
0a9e1e11 | 1992 | return false; |
3fbfbf7a PM |
1993 | rsp->qlen = 0; |
1994 | rsp->qlen_lazy = 0; | |
1995 | ||
1996 | /* First, enqueue the donelist, if any. This preserves CB ordering. */ | |
1997 | if (rsp->orphan_donelist != NULL) { | |
1998 | __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist, | |
96d3fd0d | 1999 | rsp->orphan_donetail, ql, qll, flags); |
3fbfbf7a PM |
2000 | ql = qll = 0; |
2001 | rsp->orphan_donelist = NULL; | |
2002 | rsp->orphan_donetail = &rsp->orphan_donelist; | |
2003 | } | |
2004 | if (rsp->orphan_nxtlist != NULL) { | |
2005 | __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist, | |
96d3fd0d | 2006 | rsp->orphan_nxttail, ql, qll, flags); |
3fbfbf7a PM |
2007 | ql = qll = 0; |
2008 | rsp->orphan_nxtlist = NULL; | |
2009 | rsp->orphan_nxttail = &rsp->orphan_nxtlist; | |
2010 | } | |
0a9e1e11 | 2011 | return true; |
3fbfbf7a PM |
2012 | } |
2013 | ||
2014 | /* | |
34ed6246 PM |
2015 | * If necessary, kick off a new grace period, and either way wait |
2016 | * for a subsequent grace period to complete. | |
3fbfbf7a | 2017 | */ |
34ed6246 | 2018 | static void rcu_nocb_wait_gp(struct rcu_data *rdp) |
3fbfbf7a | 2019 | { |
34ed6246 | 2020 | unsigned long c; |
dae6e64d | 2021 | bool d; |
34ed6246 | 2022 | unsigned long flags; |
48a7639c | 2023 | bool needwake; |
34ed6246 PM |
2024 | struct rcu_node *rnp = rdp->mynode; |
2025 | ||
2026 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
6303b9c8 | 2027 | smp_mb__after_unlock_lock(); |
48a7639c | 2028 | needwake = rcu_start_future_gp(rnp, rdp, &c); |
0446be48 | 2029 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
48a7639c PM |
2030 | if (needwake) |
2031 | rcu_gp_kthread_wake(rdp->rsp); | |
3fbfbf7a PM |
2032 | |
2033 | /* | |
34ed6246 PM |
2034 | * Wait for the grace period. Do so interruptibly to avoid messing |
2035 | * up the load average. | |
3fbfbf7a | 2036 | */ |
f7f7bac9 | 2037 | trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait")); |
34ed6246 | 2038 | for (;;) { |
dae6e64d PM |
2039 | wait_event_interruptible( |
2040 | rnp->nocb_gp_wq[c & 0x1], | |
7d0ae808 | 2041 | (d = ULONG_CMP_GE(READ_ONCE(rnp->completed), c))); |
dae6e64d | 2042 | if (likely(d)) |
34ed6246 | 2043 | break; |
73a860cd | 2044 | WARN_ON(signal_pending(current)); |
f7f7bac9 | 2045 | trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait")); |
34ed6246 | 2046 | } |
f7f7bac9 | 2047 | trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait")); |
34ed6246 | 2048 | smp_mb(); /* Ensure that CB invocation happens after GP end. */ |
3fbfbf7a PM |
2049 | } |
2050 | ||
fbce7497 PM |
2051 | /* |
2052 | * Leaders come here to wait for additional callbacks to show up. | |
2053 | * This function does not return until callbacks appear. | |
2054 | */ | |
2055 | static void nocb_leader_wait(struct rcu_data *my_rdp) | |
2056 | { | |
2057 | bool firsttime = true; | |
2058 | bool gotcbs; | |
2059 | struct rcu_data *rdp; | |
2060 | struct rcu_head **tail; | |
2061 | ||
2062 | wait_again: | |
2063 | ||
2064 | /* Wait for callbacks to appear. */ | |
2065 | if (!rcu_nocb_poll) { | |
2066 | trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Sleep"); | |
2067 | wait_event_interruptible(my_rdp->nocb_wq, | |
7d0ae808 | 2068 | !READ_ONCE(my_rdp->nocb_leader_sleep)); |
fbce7497 PM |
2069 | /* Memory barrier handled by smp_mb() calls below and repoll. */ |
2070 | } else if (firsttime) { | |
2071 | firsttime = false; /* Don't drown trace log with "Poll"! */ | |
2072 | trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Poll"); | |
2073 | } | |
2074 | ||
2075 | /* | |
2076 | * Each pass through the following loop checks a follower for CBs. | |
2077 | * We are our own first follower. Any CBs found are moved to | |
2078 | * nocb_gp_head, where they await a grace period. | |
2079 | */ | |
2080 | gotcbs = false; | |
2081 | for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) { | |
7d0ae808 | 2082 | rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head); |
fbce7497 PM |
2083 | if (!rdp->nocb_gp_head) |
2084 | continue; /* No CBs here, try next follower. */ | |
2085 | ||
2086 | /* Move callbacks to wait-for-GP list, which is empty. */ | |
7d0ae808 | 2087 | WRITE_ONCE(rdp->nocb_head, NULL); |
fbce7497 | 2088 | rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head); |
fbce7497 PM |
2089 | gotcbs = true; |
2090 | } | |
2091 | ||
2092 | /* | |
2093 | * If there were no callbacks, sleep a bit, rescan after a | |
2094 | * memory barrier, and go retry. | |
2095 | */ | |
2096 | if (unlikely(!gotcbs)) { | |
2097 | if (!rcu_nocb_poll) | |
2098 | trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, | |
2099 | "WokeEmpty"); | |
73a860cd | 2100 | WARN_ON(signal_pending(current)); |
fbce7497 PM |
2101 | schedule_timeout_interruptible(1); |
2102 | ||
2103 | /* Rescan in case we were a victim of memory ordering. */ | |
11ed7f93 PK |
2104 | my_rdp->nocb_leader_sleep = true; |
2105 | smp_mb(); /* Ensure _sleep true before scan. */ | |
fbce7497 | 2106 | for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) |
7d0ae808 | 2107 | if (READ_ONCE(rdp->nocb_head)) { |
fbce7497 | 2108 | /* Found CB, so short-circuit next wait. */ |
11ed7f93 | 2109 | my_rdp->nocb_leader_sleep = false; |
fbce7497 PM |
2110 | break; |
2111 | } | |
2112 | goto wait_again; | |
2113 | } | |
2114 | ||
2115 | /* Wait for one grace period. */ | |
2116 | rcu_nocb_wait_gp(my_rdp); | |
2117 | ||
2118 | /* | |
11ed7f93 PK |
2119 | * We left ->nocb_leader_sleep unset to reduce cache thrashing. |
2120 | * We set it now, but recheck for new callbacks while | |
fbce7497 PM |
2121 | * traversing our follower list. |
2122 | */ | |
11ed7f93 PK |
2123 | my_rdp->nocb_leader_sleep = true; |
2124 | smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */ | |
fbce7497 PM |
2125 | |
2126 | /* Each pass through the following loop wakes a follower, if needed. */ | |
2127 | for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) { | |
7d0ae808 | 2128 | if (READ_ONCE(rdp->nocb_head)) |
11ed7f93 | 2129 | my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/ |
fbce7497 PM |
2130 | if (!rdp->nocb_gp_head) |
2131 | continue; /* No CBs, so no need to wake follower. */ | |
2132 | ||
2133 | /* Append callbacks to follower's "done" list. */ | |
2134 | tail = xchg(&rdp->nocb_follower_tail, rdp->nocb_gp_tail); | |
2135 | *tail = rdp->nocb_gp_head; | |
c847f142 | 2136 | smp_mb__after_atomic(); /* Store *tail before wakeup. */ |
fbce7497 PM |
2137 | if (rdp != my_rdp && tail == &rdp->nocb_follower_head) { |
2138 | /* | |
2139 | * List was empty, wake up the follower. | |
2140 | * Memory barriers supplied by atomic_long_add(). | |
2141 | */ | |
2142 | wake_up(&rdp->nocb_wq); | |
2143 | } | |
2144 | } | |
2145 | ||
2146 | /* If we (the leader) don't have CBs, go wait some more. */ | |
2147 | if (!my_rdp->nocb_follower_head) | |
2148 | goto wait_again; | |
2149 | } | |
2150 | ||
2151 | /* | |
2152 | * Followers come here to wait for additional callbacks to show up. | |
2153 | * This function does not return until callbacks appear. | |
2154 | */ | |
2155 | static void nocb_follower_wait(struct rcu_data *rdp) | |
2156 | { | |
2157 | bool firsttime = true; | |
2158 | ||
2159 | for (;;) { | |
2160 | if (!rcu_nocb_poll) { | |
2161 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, | |
2162 | "FollowerSleep"); | |
2163 | wait_event_interruptible(rdp->nocb_wq, | |
7d0ae808 | 2164 | READ_ONCE(rdp->nocb_follower_head)); |
fbce7497 PM |
2165 | } else if (firsttime) { |
2166 | /* Don't drown trace log with "Poll"! */ | |
2167 | firsttime = false; | |
2168 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "Poll"); | |
2169 | } | |
2170 | if (smp_load_acquire(&rdp->nocb_follower_head)) { | |
2171 | /* ^^^ Ensure CB invocation follows _head test. */ | |
2172 | return; | |
2173 | } | |
2174 | if (!rcu_nocb_poll) | |
2175 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, | |
2176 | "WokeEmpty"); | |
73a860cd | 2177 | WARN_ON(signal_pending(current)); |
fbce7497 PM |
2178 | schedule_timeout_interruptible(1); |
2179 | } | |
2180 | } | |
2181 | ||
3fbfbf7a PM |
2182 | /* |
2183 | * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes | |
fbce7497 PM |
2184 | * callbacks queued by the corresponding no-CBs CPU, however, there is |
2185 | * an optional leader-follower relationship so that the grace-period | |
2186 | * kthreads don't have to do quite so many wakeups. | |
3fbfbf7a PM |
2187 | */ |
2188 | static int rcu_nocb_kthread(void *arg) | |
2189 | { | |
2190 | int c, cl; | |
2191 | struct rcu_head *list; | |
2192 | struct rcu_head *next; | |
2193 | struct rcu_head **tail; | |
2194 | struct rcu_data *rdp = arg; | |
2195 | ||
2196 | /* Each pass through this loop invokes one batch of callbacks */ | |
2197 | for (;;) { | |
fbce7497 PM |
2198 | /* Wait for callbacks. */ |
2199 | if (rdp->nocb_leader == rdp) | |
2200 | nocb_leader_wait(rdp); | |
2201 | else | |
2202 | nocb_follower_wait(rdp); | |
2203 | ||
2204 | /* Pull the ready-to-invoke callbacks onto local list. */ | |
7d0ae808 | 2205 | list = READ_ONCE(rdp->nocb_follower_head); |
fbce7497 PM |
2206 | BUG_ON(!list); |
2207 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "WokeNonEmpty"); | |
7d0ae808 | 2208 | WRITE_ONCE(rdp->nocb_follower_head, NULL); |
fbce7497 | 2209 | tail = xchg(&rdp->nocb_follower_tail, &rdp->nocb_follower_head); |
3fbfbf7a PM |
2210 | |
2211 | /* Each pass through the following loop invokes a callback. */ | |
41050a00 PM |
2212 | trace_rcu_batch_start(rdp->rsp->name, |
2213 | atomic_long_read(&rdp->nocb_q_count_lazy), | |
2214 | atomic_long_read(&rdp->nocb_q_count), -1); | |
3fbfbf7a PM |
2215 | c = cl = 0; |
2216 | while (list) { | |
2217 | next = list->next; | |
2218 | /* Wait for enqueuing to complete, if needed. */ | |
2219 | while (next == NULL && &list->next != tail) { | |
69a79bb1 PM |
2220 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
2221 | TPS("WaitQueue")); | |
3fbfbf7a | 2222 | schedule_timeout_interruptible(1); |
69a79bb1 PM |
2223 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
2224 | TPS("WokeQueue")); | |
3fbfbf7a PM |
2225 | next = list->next; |
2226 | } | |
2227 | debug_rcu_head_unqueue(list); | |
2228 | local_bh_disable(); | |
2229 | if (__rcu_reclaim(rdp->rsp->name, list)) | |
2230 | cl++; | |
2231 | c++; | |
2232 | local_bh_enable(); | |
2233 | list = next; | |
2234 | } | |
2235 | trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1); | |
41050a00 PM |
2236 | smp_mb__before_atomic(); /* _add after CB invocation. */ |
2237 | atomic_long_add(-c, &rdp->nocb_q_count); | |
2238 | atomic_long_add(-cl, &rdp->nocb_q_count_lazy); | |
c635a4e1 | 2239 | rdp->n_nocbs_invoked += c; |
3fbfbf7a PM |
2240 | } |
2241 | return 0; | |
2242 | } | |
2243 | ||
96d3fd0d | 2244 | /* Is a deferred wakeup of rcu_nocb_kthread() required? */ |
9fdd3bc9 | 2245 | static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) |
96d3fd0d | 2246 | { |
7d0ae808 | 2247 | return READ_ONCE(rdp->nocb_defer_wakeup); |
96d3fd0d PM |
2248 | } |
2249 | ||
2250 | /* Do a deferred wakeup of rcu_nocb_kthread(). */ | |
2251 | static void do_nocb_deferred_wakeup(struct rcu_data *rdp) | |
2252 | { | |
9fdd3bc9 PM |
2253 | int ndw; |
2254 | ||
96d3fd0d PM |
2255 | if (!rcu_nocb_need_deferred_wakeup(rdp)) |
2256 | return; | |
7d0ae808 PM |
2257 | ndw = READ_ONCE(rdp->nocb_defer_wakeup); |
2258 | WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOGP_WAKE_NOT); | |
9fdd3bc9 PM |
2259 | wake_nocb_leader(rdp, ndw == RCU_NOGP_WAKE_FORCE); |
2260 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake")); | |
96d3fd0d PM |
2261 | } |
2262 | ||
f4579fc5 PM |
2263 | void __init rcu_init_nohz(void) |
2264 | { | |
2265 | int cpu; | |
2266 | bool need_rcu_nocb_mask = true; | |
2267 | struct rcu_state *rsp; | |
2268 | ||
2269 | #ifdef CONFIG_RCU_NOCB_CPU_NONE | |
2270 | need_rcu_nocb_mask = false; | |
2271 | #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */ | |
2272 | ||
2273 | #if defined(CONFIG_NO_HZ_FULL) | |
2274 | if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask)) | |
2275 | need_rcu_nocb_mask = true; | |
2276 | #endif /* #if defined(CONFIG_NO_HZ_FULL) */ | |
2277 | ||
2278 | if (!have_rcu_nocb_mask && need_rcu_nocb_mask) { | |
949cccdb PK |
2279 | if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) { |
2280 | pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n"); | |
2281 | return; | |
2282 | } | |
f4579fc5 PM |
2283 | have_rcu_nocb_mask = true; |
2284 | } | |
2285 | if (!have_rcu_nocb_mask) | |
2286 | return; | |
2287 | ||
2288 | #ifdef CONFIG_RCU_NOCB_CPU_ZERO | |
2289 | pr_info("\tOffload RCU callbacks from CPU 0\n"); | |
2290 | cpumask_set_cpu(0, rcu_nocb_mask); | |
2291 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */ | |
2292 | #ifdef CONFIG_RCU_NOCB_CPU_ALL | |
2293 | pr_info("\tOffload RCU callbacks from all CPUs\n"); | |
2294 | cpumask_copy(rcu_nocb_mask, cpu_possible_mask); | |
2295 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */ | |
2296 | #if defined(CONFIG_NO_HZ_FULL) | |
2297 | if (tick_nohz_full_running) | |
2298 | cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask); | |
2299 | #endif /* #if defined(CONFIG_NO_HZ_FULL) */ | |
2300 | ||
2301 | if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { | |
2302 | pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n"); | |
2303 | cpumask_and(rcu_nocb_mask, cpu_possible_mask, | |
2304 | rcu_nocb_mask); | |
2305 | } | |
ad853b48 TH |
2306 | pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n", |
2307 | cpumask_pr_args(rcu_nocb_mask)); | |
f4579fc5 PM |
2308 | if (rcu_nocb_poll) |
2309 | pr_info("\tPoll for callbacks from no-CBs CPUs.\n"); | |
2310 | ||
2311 | for_each_rcu_flavor(rsp) { | |
34404ca8 PM |
2312 | for_each_cpu(cpu, rcu_nocb_mask) |
2313 | init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu)); | |
35ce7f29 | 2314 | rcu_organize_nocb_kthreads(rsp); |
f4579fc5 | 2315 | } |
96d3fd0d PM |
2316 | } |
2317 | ||
3fbfbf7a PM |
2318 | /* Initialize per-rcu_data variables for no-CBs CPUs. */ |
2319 | static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) | |
2320 | { | |
2321 | rdp->nocb_tail = &rdp->nocb_head; | |
2322 | init_waitqueue_head(&rdp->nocb_wq); | |
fbce7497 | 2323 | rdp->nocb_follower_tail = &rdp->nocb_follower_head; |
3fbfbf7a PM |
2324 | } |
2325 | ||
35ce7f29 PM |
2326 | /* |
2327 | * If the specified CPU is a no-CBs CPU that does not already have its | |
2328 | * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are | |
2329 | * brought online out of order, this can require re-organizing the | |
2330 | * leader-follower relationships. | |
2331 | */ | |
2332 | static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu) | |
2333 | { | |
2334 | struct rcu_data *rdp; | |
2335 | struct rcu_data *rdp_last; | |
2336 | struct rcu_data *rdp_old_leader; | |
2337 | struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu); | |
2338 | struct task_struct *t; | |
2339 | ||
2340 | /* | |
2341 | * If this isn't a no-CBs CPU or if it already has an rcuo kthread, | |
2342 | * then nothing to do. | |
2343 | */ | |
2344 | if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread) | |
2345 | return; | |
2346 | ||
2347 | /* If we didn't spawn the leader first, reorganize! */ | |
2348 | rdp_old_leader = rdp_spawn->nocb_leader; | |
2349 | if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) { | |
2350 | rdp_last = NULL; | |
2351 | rdp = rdp_old_leader; | |
2352 | do { | |
2353 | rdp->nocb_leader = rdp_spawn; | |
2354 | if (rdp_last && rdp != rdp_spawn) | |
2355 | rdp_last->nocb_next_follower = rdp; | |
bbe5d7a9 PM |
2356 | if (rdp == rdp_spawn) { |
2357 | rdp = rdp->nocb_next_follower; | |
2358 | } else { | |
2359 | rdp_last = rdp; | |
2360 | rdp = rdp->nocb_next_follower; | |
2361 | rdp_last->nocb_next_follower = NULL; | |
2362 | } | |
35ce7f29 PM |
2363 | } while (rdp); |
2364 | rdp_spawn->nocb_next_follower = rdp_old_leader; | |
2365 | } | |
2366 | ||
2367 | /* Spawn the kthread for this CPU and RCU flavor. */ | |
2368 | t = kthread_run(rcu_nocb_kthread, rdp_spawn, | |
2369 | "rcuo%c/%d", rsp->abbr, cpu); | |
2370 | BUG_ON(IS_ERR(t)); | |
7d0ae808 | 2371 | WRITE_ONCE(rdp_spawn->nocb_kthread, t); |
35ce7f29 PM |
2372 | } |
2373 | ||
2374 | /* | |
2375 | * If the specified CPU is a no-CBs CPU that does not already have its | |
2376 | * rcuo kthreads, spawn them. | |
2377 | */ | |
2378 | static void rcu_spawn_all_nocb_kthreads(int cpu) | |
2379 | { | |
2380 | struct rcu_state *rsp; | |
2381 | ||
2382 | if (rcu_scheduler_fully_active) | |
2383 | for_each_rcu_flavor(rsp) | |
2384 | rcu_spawn_one_nocb_kthread(rsp, cpu); | |
2385 | } | |
2386 | ||
2387 | /* | |
2388 | * Once the scheduler is running, spawn rcuo kthreads for all online | |
2389 | * no-CBs CPUs. This assumes that the early_initcall()s happen before | |
2390 | * non-boot CPUs come online -- if this changes, we will need to add | |
2391 | * some mutual exclusion. | |
2392 | */ | |
2393 | static void __init rcu_spawn_nocb_kthreads(void) | |
2394 | { | |
2395 | int cpu; | |
2396 | ||
2397 | for_each_online_cpu(cpu) | |
2398 | rcu_spawn_all_nocb_kthreads(cpu); | |
2399 | } | |
2400 | ||
fbce7497 PM |
2401 | /* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */ |
2402 | static int rcu_nocb_leader_stride = -1; | |
2403 | module_param(rcu_nocb_leader_stride, int, 0444); | |
2404 | ||
2405 | /* | |
35ce7f29 | 2406 | * Initialize leader-follower relationships for all no-CBs CPU. |
fbce7497 | 2407 | */ |
35ce7f29 | 2408 | static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp) |
3fbfbf7a PM |
2409 | { |
2410 | int cpu; | |
fbce7497 PM |
2411 | int ls = rcu_nocb_leader_stride; |
2412 | int nl = 0; /* Next leader. */ | |
3fbfbf7a | 2413 | struct rcu_data *rdp; |
fbce7497 PM |
2414 | struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */ |
2415 | struct rcu_data *rdp_prev = NULL; | |
3fbfbf7a | 2416 | |
22c2f669 | 2417 | if (!have_rcu_nocb_mask) |
3fbfbf7a | 2418 | return; |
fbce7497 PM |
2419 | if (ls == -1) { |
2420 | ls = int_sqrt(nr_cpu_ids); | |
2421 | rcu_nocb_leader_stride = ls; | |
2422 | } | |
2423 | ||
2424 | /* | |
2425 | * Each pass through this loop sets up one rcu_data structure and | |
2426 | * spawns one rcu_nocb_kthread(). | |
2427 | */ | |
3fbfbf7a PM |
2428 | for_each_cpu(cpu, rcu_nocb_mask) { |
2429 | rdp = per_cpu_ptr(rsp->rda, cpu); | |
fbce7497 PM |
2430 | if (rdp->cpu >= nl) { |
2431 | /* New leader, set up for followers & next leader. */ | |
2432 | nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls; | |
2433 | rdp->nocb_leader = rdp; | |
2434 | rdp_leader = rdp; | |
2435 | } else { | |
2436 | /* Another follower, link to previous leader. */ | |
2437 | rdp->nocb_leader = rdp_leader; | |
2438 | rdp_prev->nocb_next_follower = rdp; | |
2439 | } | |
2440 | rdp_prev = rdp; | |
3fbfbf7a PM |
2441 | } |
2442 | } | |
2443 | ||
2444 | /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */ | |
34ed6246 | 2445 | static bool init_nocb_callback_list(struct rcu_data *rdp) |
3fbfbf7a | 2446 | { |
22c2f669 | 2447 | if (!rcu_is_nocb_cpu(rdp->cpu)) |
34ed6246 | 2448 | return false; |
22c2f669 | 2449 | |
34404ca8 PM |
2450 | /* If there are early-boot callbacks, move them to nocb lists. */ |
2451 | if (rdp->nxtlist) { | |
2452 | rdp->nocb_head = rdp->nxtlist; | |
2453 | rdp->nocb_tail = rdp->nxttail[RCU_NEXT_TAIL]; | |
2454 | atomic_long_set(&rdp->nocb_q_count, rdp->qlen); | |
2455 | atomic_long_set(&rdp->nocb_q_count_lazy, rdp->qlen_lazy); | |
2456 | rdp->nxtlist = NULL; | |
2457 | rdp->qlen = 0; | |
2458 | rdp->qlen_lazy = 0; | |
2459 | } | |
3fbfbf7a | 2460 | rdp->nxttail[RCU_NEXT_TAIL] = NULL; |
34ed6246 | 2461 | return true; |
3fbfbf7a PM |
2462 | } |
2463 | ||
34ed6246 PM |
2464 | #else /* #ifdef CONFIG_RCU_NOCB_CPU */ |
2465 | ||
d7e29933 PM |
2466 | static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) |
2467 | { | |
2468 | WARN_ON_ONCE(1); /* Should be dead code. */ | |
2469 | return false; | |
2470 | } | |
2471 | ||
0446be48 | 2472 | static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) |
3fbfbf7a | 2473 | { |
3fbfbf7a PM |
2474 | } |
2475 | ||
dae6e64d PM |
2476 | static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) |
2477 | { | |
2478 | } | |
2479 | ||
2480 | static void rcu_init_one_nocb(struct rcu_node *rnp) | |
2481 | { | |
2482 | } | |
3fbfbf7a | 2483 | |
3fbfbf7a | 2484 | static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, |
96d3fd0d | 2485 | bool lazy, unsigned long flags) |
3fbfbf7a | 2486 | { |
4afc7e26 | 2487 | return false; |
3fbfbf7a PM |
2488 | } |
2489 | ||
2490 | static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, | |
96d3fd0d PM |
2491 | struct rcu_data *rdp, |
2492 | unsigned long flags) | |
3fbfbf7a | 2493 | { |
f4aa84ba | 2494 | return false; |
3fbfbf7a PM |
2495 | } |
2496 | ||
3fbfbf7a PM |
2497 | static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) |
2498 | { | |
2499 | } | |
2500 | ||
9fdd3bc9 | 2501 | static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) |
96d3fd0d PM |
2502 | { |
2503 | return false; | |
2504 | } | |
2505 | ||
2506 | static void do_nocb_deferred_wakeup(struct rcu_data *rdp) | |
2507 | { | |
2508 | } | |
2509 | ||
35ce7f29 PM |
2510 | static void rcu_spawn_all_nocb_kthreads(int cpu) |
2511 | { | |
2512 | } | |
2513 | ||
2514 | static void __init rcu_spawn_nocb_kthreads(void) | |
3fbfbf7a PM |
2515 | { |
2516 | } | |
2517 | ||
34ed6246 | 2518 | static bool init_nocb_callback_list(struct rcu_data *rdp) |
3fbfbf7a | 2519 | { |
34ed6246 | 2520 | return false; |
3fbfbf7a PM |
2521 | } |
2522 | ||
2523 | #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ | |
65d798f0 PM |
2524 | |
2525 | /* | |
2526 | * An adaptive-ticks CPU can potentially execute in kernel mode for an | |
2527 | * arbitrarily long period of time with the scheduling-clock tick turned | |
2528 | * off. RCU will be paying attention to this CPU because it is in the | |
2529 | * kernel, but the CPU cannot be guaranteed to be executing the RCU state | |
2530 | * machine because the scheduling-clock tick has been disabled. Therefore, | |
2531 | * if an adaptive-ticks CPU is failing to respond to the current grace | |
2532 | * period and has not be idle from an RCU perspective, kick it. | |
2533 | */ | |
4a81e832 | 2534 | static void __maybe_unused rcu_kick_nohz_cpu(int cpu) |
65d798f0 PM |
2535 | { |
2536 | #ifdef CONFIG_NO_HZ_FULL | |
2537 | if (tick_nohz_full_cpu(cpu)) | |
2538 | smp_send_reschedule(cpu); | |
2539 | #endif /* #ifdef CONFIG_NO_HZ_FULL */ | |
2540 | } | |
2333210b PM |
2541 | |
2542 | ||
2543 | #ifdef CONFIG_NO_HZ_FULL_SYSIDLE | |
2544 | ||
0edd1b17 | 2545 | static int full_sysidle_state; /* Current system-idle state. */ |
d4bd54fb PM |
2546 | #define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */ |
2547 | #define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */ | |
2548 | #define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */ | |
2549 | #define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */ | |
2550 | #define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */ | |
2551 | ||
eb348b89 PM |
2552 | /* |
2553 | * Invoked to note exit from irq or task transition to idle. Note that | |
2554 | * usermode execution does -not- count as idle here! After all, we want | |
2555 | * to detect full-system idle states, not RCU quiescent states and grace | |
2556 | * periods. The caller must have disabled interrupts. | |
2557 | */ | |
28ced795 | 2558 | static void rcu_sysidle_enter(int irq) |
eb348b89 PM |
2559 | { |
2560 | unsigned long j; | |
28ced795 | 2561 | struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
eb348b89 | 2562 | |
663e1310 PM |
2563 | /* If there are no nohz_full= CPUs, no need to track this. */ |
2564 | if (!tick_nohz_full_enabled()) | |
2565 | return; | |
2566 | ||
eb348b89 PM |
2567 | /* Adjust nesting, check for fully idle. */ |
2568 | if (irq) { | |
2569 | rdtp->dynticks_idle_nesting--; | |
2570 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); | |
2571 | if (rdtp->dynticks_idle_nesting != 0) | |
2572 | return; /* Still not fully idle. */ | |
2573 | } else { | |
2574 | if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) == | |
2575 | DYNTICK_TASK_NEST_VALUE) { | |
2576 | rdtp->dynticks_idle_nesting = 0; | |
2577 | } else { | |
2578 | rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE; | |
2579 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); | |
2580 | return; /* Still not fully idle. */ | |
2581 | } | |
2582 | } | |
2583 | ||
2584 | /* Record start of fully idle period. */ | |
2585 | j = jiffies; | |
7d0ae808 | 2586 | WRITE_ONCE(rdtp->dynticks_idle_jiffies, j); |
4e857c58 | 2587 | smp_mb__before_atomic(); |
eb348b89 | 2588 | atomic_inc(&rdtp->dynticks_idle); |
4e857c58 | 2589 | smp_mb__after_atomic(); |
eb348b89 PM |
2590 | WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1); |
2591 | } | |
2592 | ||
0edd1b17 PM |
2593 | /* |
2594 | * Unconditionally force exit from full system-idle state. This is | |
2595 | * invoked when a normal CPU exits idle, but must be called separately | |
2596 | * for the timekeeping CPU (tick_do_timer_cpu). The reason for this | |
2597 | * is that the timekeeping CPU is permitted to take scheduling-clock | |
2598 | * interrupts while the system is in system-idle state, and of course | |
2599 | * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock | |
2600 | * interrupt from any other type of interrupt. | |
2601 | */ | |
2602 | void rcu_sysidle_force_exit(void) | |
2603 | { | |
7d0ae808 | 2604 | int oldstate = READ_ONCE(full_sysidle_state); |
0edd1b17 PM |
2605 | int newoldstate; |
2606 | ||
2607 | /* | |
2608 | * Each pass through the following loop attempts to exit full | |
2609 | * system-idle state. If contention proves to be a problem, | |
2610 | * a trylock-based contention tree could be used here. | |
2611 | */ | |
2612 | while (oldstate > RCU_SYSIDLE_SHORT) { | |
2613 | newoldstate = cmpxchg(&full_sysidle_state, | |
2614 | oldstate, RCU_SYSIDLE_NOT); | |
2615 | if (oldstate == newoldstate && | |
2616 | oldstate == RCU_SYSIDLE_FULL_NOTED) { | |
2617 | rcu_kick_nohz_cpu(tick_do_timer_cpu); | |
2618 | return; /* We cleared it, done! */ | |
2619 | } | |
2620 | oldstate = newoldstate; | |
2621 | } | |
2622 | smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */ | |
2623 | } | |
2624 | ||
eb348b89 PM |
2625 | /* |
2626 | * Invoked to note entry to irq or task transition from idle. Note that | |
2627 | * usermode execution does -not- count as idle here! The caller must | |
2628 | * have disabled interrupts. | |
2629 | */ | |
28ced795 | 2630 | static void rcu_sysidle_exit(int irq) |
eb348b89 | 2631 | { |
28ced795 CL |
2632 | struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
2633 | ||
663e1310 PM |
2634 | /* If there are no nohz_full= CPUs, no need to track this. */ |
2635 | if (!tick_nohz_full_enabled()) | |
2636 | return; | |
2637 | ||
eb348b89 PM |
2638 | /* Adjust nesting, check for already non-idle. */ |
2639 | if (irq) { | |
2640 | rdtp->dynticks_idle_nesting++; | |
2641 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); | |
2642 | if (rdtp->dynticks_idle_nesting != 1) | |
2643 | return; /* Already non-idle. */ | |
2644 | } else { | |
2645 | /* | |
2646 | * Allow for irq misnesting. Yes, it really is possible | |
2647 | * to enter an irq handler then never leave it, and maybe | |
2648 | * also vice versa. Handle both possibilities. | |
2649 | */ | |
2650 | if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) { | |
2651 | rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE; | |
2652 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); | |
2653 | return; /* Already non-idle. */ | |
2654 | } else { | |
2655 | rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE; | |
2656 | } | |
2657 | } | |
2658 | ||
2659 | /* Record end of idle period. */ | |
4e857c58 | 2660 | smp_mb__before_atomic(); |
eb348b89 | 2661 | atomic_inc(&rdtp->dynticks_idle); |
4e857c58 | 2662 | smp_mb__after_atomic(); |
eb348b89 | 2663 | WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1)); |
0edd1b17 PM |
2664 | |
2665 | /* | |
2666 | * If we are the timekeeping CPU, we are permitted to be non-idle | |
2667 | * during a system-idle state. This must be the case, because | |
2668 | * the timekeeping CPU has to take scheduling-clock interrupts | |
2669 | * during the time that the system is transitioning to full | |
2670 | * system-idle state. This means that the timekeeping CPU must | |
2671 | * invoke rcu_sysidle_force_exit() directly if it does anything | |
2672 | * more than take a scheduling-clock interrupt. | |
2673 | */ | |
2674 | if (smp_processor_id() == tick_do_timer_cpu) | |
2675 | return; | |
2676 | ||
2677 | /* Update system-idle state: We are clearly no longer fully idle! */ | |
2678 | rcu_sysidle_force_exit(); | |
2679 | } | |
2680 | ||
2681 | /* | |
2682 | * Check to see if the current CPU is idle. Note that usermode execution | |
5871968d PM |
2683 | * does not count as idle. The caller must have disabled interrupts, |
2684 | * and must be running on tick_do_timer_cpu. | |
0edd1b17 PM |
2685 | */ |
2686 | static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, | |
2687 | unsigned long *maxj) | |
2688 | { | |
2689 | int cur; | |
2690 | unsigned long j; | |
2691 | struct rcu_dynticks *rdtp = rdp->dynticks; | |
2692 | ||
663e1310 PM |
2693 | /* If there are no nohz_full= CPUs, don't check system-wide idleness. */ |
2694 | if (!tick_nohz_full_enabled()) | |
2695 | return; | |
2696 | ||
0edd1b17 PM |
2697 | /* |
2698 | * If some other CPU has already reported non-idle, if this is | |
2699 | * not the flavor of RCU that tracks sysidle state, or if this | |
2700 | * is an offline or the timekeeping CPU, nothing to do. | |
2701 | */ | |
417e8d26 | 2702 | if (!*isidle || rdp->rsp != rcu_state_p || |
0edd1b17 PM |
2703 | cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu) |
2704 | return; | |
5871968d PM |
2705 | /* Verify affinity of current kthread. */ |
2706 | WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); | |
0edd1b17 PM |
2707 | |
2708 | /* Pick up current idle and NMI-nesting counter and check. */ | |
2709 | cur = atomic_read(&rdtp->dynticks_idle); | |
2710 | if (cur & 0x1) { | |
2711 | *isidle = false; /* We are not idle! */ | |
2712 | return; | |
2713 | } | |
2714 | smp_mb(); /* Read counters before timestamps. */ | |
2715 | ||
2716 | /* Pick up timestamps. */ | |
7d0ae808 | 2717 | j = READ_ONCE(rdtp->dynticks_idle_jiffies); |
0edd1b17 PM |
2718 | /* If this CPU entered idle more recently, update maxj timestamp. */ |
2719 | if (ULONG_CMP_LT(*maxj, j)) | |
2720 | *maxj = j; | |
2721 | } | |
2722 | ||
2723 | /* | |
2724 | * Is this the flavor of RCU that is handling full-system idle? | |
2725 | */ | |
2726 | static bool is_sysidle_rcu_state(struct rcu_state *rsp) | |
2727 | { | |
417e8d26 | 2728 | return rsp == rcu_state_p; |
0edd1b17 PM |
2729 | } |
2730 | ||
2731 | /* | |
2732 | * Return a delay in jiffies based on the number of CPUs, rcu_node | |
2733 | * leaf fanout, and jiffies tick rate. The idea is to allow larger | |
2734 | * systems more time to transition to full-idle state in order to | |
2735 | * avoid the cache thrashing that otherwise occur on the state variable. | |
2736 | * Really small systems (less than a couple of tens of CPUs) should | |
2737 | * instead use a single global atomically incremented counter, and later | |
2738 | * versions of this will automatically reconfigure themselves accordingly. | |
2739 | */ | |
2740 | static unsigned long rcu_sysidle_delay(void) | |
2741 | { | |
2742 | if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) | |
2743 | return 0; | |
2744 | return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000); | |
2745 | } | |
2746 | ||
2747 | /* | |
2748 | * Advance the full-system-idle state. This is invoked when all of | |
2749 | * the non-timekeeping CPUs are idle. | |
2750 | */ | |
2751 | static void rcu_sysidle(unsigned long j) | |
2752 | { | |
2753 | /* Check the current state. */ | |
7d0ae808 | 2754 | switch (READ_ONCE(full_sysidle_state)) { |
0edd1b17 PM |
2755 | case RCU_SYSIDLE_NOT: |
2756 | ||
2757 | /* First time all are idle, so note a short idle period. */ | |
7d0ae808 | 2758 | WRITE_ONCE(full_sysidle_state, RCU_SYSIDLE_SHORT); |
0edd1b17 PM |
2759 | break; |
2760 | ||
2761 | case RCU_SYSIDLE_SHORT: | |
2762 | ||
2763 | /* | |
2764 | * Idle for a bit, time to advance to next state? | |
2765 | * cmpxchg failure means race with non-idle, let them win. | |
2766 | */ | |
2767 | if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) | |
2768 | (void)cmpxchg(&full_sysidle_state, | |
2769 | RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG); | |
2770 | break; | |
2771 | ||
2772 | case RCU_SYSIDLE_LONG: | |
2773 | ||
2774 | /* | |
2775 | * Do an additional check pass before advancing to full. | |
2776 | * cmpxchg failure means race with non-idle, let them win. | |
2777 | */ | |
2778 | if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) | |
2779 | (void)cmpxchg(&full_sysidle_state, | |
2780 | RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL); | |
2781 | break; | |
2782 | ||
2783 | default: | |
2784 | break; | |
2785 | } | |
2786 | } | |
2787 | ||
2788 | /* | |
2789 | * Found a non-idle non-timekeeping CPU, so kick the system-idle state | |
2790 | * back to the beginning. | |
2791 | */ | |
2792 | static void rcu_sysidle_cancel(void) | |
2793 | { | |
2794 | smp_mb(); | |
becb41bf | 2795 | if (full_sysidle_state > RCU_SYSIDLE_SHORT) |
7d0ae808 | 2796 | WRITE_ONCE(full_sysidle_state, RCU_SYSIDLE_NOT); |
0edd1b17 PM |
2797 | } |
2798 | ||
2799 | /* | |
2800 | * Update the sysidle state based on the results of a force-quiescent-state | |
2801 | * scan of the CPUs' dyntick-idle state. | |
2802 | */ | |
2803 | static void rcu_sysidle_report(struct rcu_state *rsp, int isidle, | |
2804 | unsigned long maxj, bool gpkt) | |
2805 | { | |
417e8d26 | 2806 | if (rsp != rcu_state_p) |
0edd1b17 PM |
2807 | return; /* Wrong flavor, ignore. */ |
2808 | if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) | |
2809 | return; /* Running state machine from timekeeping CPU. */ | |
2810 | if (isidle) | |
2811 | rcu_sysidle(maxj); /* More idle! */ | |
2812 | else | |
2813 | rcu_sysidle_cancel(); /* Idle is over. */ | |
2814 | } | |
2815 | ||
2816 | /* | |
2817 | * Wrapper for rcu_sysidle_report() when called from the grace-period | |
2818 | * kthread's context. | |
2819 | */ | |
2820 | static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, | |
2821 | unsigned long maxj) | |
2822 | { | |
663e1310 PM |
2823 | /* If there are no nohz_full= CPUs, no need to track this. */ |
2824 | if (!tick_nohz_full_enabled()) | |
2825 | return; | |
2826 | ||
0edd1b17 PM |
2827 | rcu_sysidle_report(rsp, isidle, maxj, true); |
2828 | } | |
2829 | ||
2830 | /* Callback and function for forcing an RCU grace period. */ | |
2831 | struct rcu_sysidle_head { | |
2832 | struct rcu_head rh; | |
2833 | int inuse; | |
2834 | }; | |
2835 | ||
2836 | static void rcu_sysidle_cb(struct rcu_head *rhp) | |
2837 | { | |
2838 | struct rcu_sysidle_head *rshp; | |
2839 | ||
2840 | /* | |
2841 | * The following memory barrier is needed to replace the | |
2842 | * memory barriers that would normally be in the memory | |
2843 | * allocator. | |
2844 | */ | |
2845 | smp_mb(); /* grace period precedes setting inuse. */ | |
2846 | ||
2847 | rshp = container_of(rhp, struct rcu_sysidle_head, rh); | |
7d0ae808 | 2848 | WRITE_ONCE(rshp->inuse, 0); |
0edd1b17 PM |
2849 | } |
2850 | ||
2851 | /* | |
2852 | * Check to see if the system is fully idle, other than the timekeeping CPU. | |
663e1310 PM |
2853 | * The caller must have disabled interrupts. This is not intended to be |
2854 | * called unless tick_nohz_full_enabled(). | |
0edd1b17 PM |
2855 | */ |
2856 | bool rcu_sys_is_idle(void) | |
2857 | { | |
2858 | static struct rcu_sysidle_head rsh; | |
7d0ae808 | 2859 | int rss = READ_ONCE(full_sysidle_state); |
0edd1b17 PM |
2860 | |
2861 | if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu)) | |
2862 | return false; | |
2863 | ||
2864 | /* Handle small-system case by doing a full scan of CPUs. */ | |
2865 | if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) { | |
2866 | int oldrss = rss - 1; | |
2867 | ||
2868 | /* | |
2869 | * One pass to advance to each state up to _FULL. | |
2870 | * Give up if any pass fails to advance the state. | |
2871 | */ | |
2872 | while (rss < RCU_SYSIDLE_FULL && oldrss < rss) { | |
2873 | int cpu; | |
2874 | bool isidle = true; | |
2875 | unsigned long maxj = jiffies - ULONG_MAX / 4; | |
2876 | struct rcu_data *rdp; | |
2877 | ||
2878 | /* Scan all the CPUs looking for nonidle CPUs. */ | |
2879 | for_each_possible_cpu(cpu) { | |
417e8d26 | 2880 | rdp = per_cpu_ptr(rcu_state_p->rda, cpu); |
0edd1b17 PM |
2881 | rcu_sysidle_check_cpu(rdp, &isidle, &maxj); |
2882 | if (!isidle) | |
2883 | break; | |
2884 | } | |
417e8d26 | 2885 | rcu_sysidle_report(rcu_state_p, isidle, maxj, false); |
0edd1b17 | 2886 | oldrss = rss; |
7d0ae808 | 2887 | rss = READ_ONCE(full_sysidle_state); |
0edd1b17 PM |
2888 | } |
2889 | } | |
2890 | ||
2891 | /* If this is the first observation of an idle period, record it. */ | |
2892 | if (rss == RCU_SYSIDLE_FULL) { | |
2893 | rss = cmpxchg(&full_sysidle_state, | |
2894 | RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED); | |
2895 | return rss == RCU_SYSIDLE_FULL; | |
2896 | } | |
2897 | ||
2898 | smp_mb(); /* ensure rss load happens before later caller actions. */ | |
2899 | ||
2900 | /* If already fully idle, tell the caller (in case of races). */ | |
2901 | if (rss == RCU_SYSIDLE_FULL_NOTED) | |
2902 | return true; | |
2903 | ||
2904 | /* | |
2905 | * If we aren't there yet, and a grace period is not in flight, | |
2906 | * initiate a grace period. Either way, tell the caller that | |
2907 | * we are not there yet. We use an xchg() rather than an assignment | |
2908 | * to make up for the memory barriers that would otherwise be | |
2909 | * provided by the memory allocator. | |
2910 | */ | |
2911 | if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL && | |
417e8d26 | 2912 | !rcu_gp_in_progress(rcu_state_p) && |
0edd1b17 PM |
2913 | !rsh.inuse && xchg(&rsh.inuse, 1) == 0) |
2914 | call_rcu(&rsh.rh, rcu_sysidle_cb); | |
2915 | return false; | |
eb348b89 PM |
2916 | } |
2917 | ||
2333210b PM |
2918 | /* |
2919 | * Initialize dynticks sysidle state for CPUs coming online. | |
2920 | */ | |
2921 | static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) | |
2922 | { | |
2923 | rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE; | |
2924 | } | |
2925 | ||
2926 | #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ | |
2927 | ||
28ced795 | 2928 | static void rcu_sysidle_enter(int irq) |
eb348b89 PM |
2929 | { |
2930 | } | |
2931 | ||
28ced795 | 2932 | static void rcu_sysidle_exit(int irq) |
eb348b89 PM |
2933 | { |
2934 | } | |
2935 | ||
0edd1b17 PM |
2936 | static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, |
2937 | unsigned long *maxj) | |
2938 | { | |
2939 | } | |
2940 | ||
2941 | static bool is_sysidle_rcu_state(struct rcu_state *rsp) | |
2942 | { | |
2943 | return false; | |
2944 | } | |
2945 | ||
2946 | static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, | |
2947 | unsigned long maxj) | |
2948 | { | |
2949 | } | |
2950 | ||
2333210b PM |
2951 | static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) |
2952 | { | |
2953 | } | |
2954 | ||
2955 | #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ | |
a096932f PM |
2956 | |
2957 | /* | |
2958 | * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the | |
2959 | * grace-period kthread will do force_quiescent_state() processing? | |
2960 | * The idea is to avoid waking up RCU core processing on such a | |
2961 | * CPU unless the grace period has extended for too long. | |
2962 | * | |
2963 | * This code relies on the fact that all NO_HZ_FULL CPUs are also | |
52e2bb95 | 2964 | * CONFIG_RCU_NOCB_CPU CPUs. |
a096932f PM |
2965 | */ |
2966 | static bool rcu_nohz_full_cpu(struct rcu_state *rsp) | |
2967 | { | |
2968 | #ifdef CONFIG_NO_HZ_FULL | |
2969 | if (tick_nohz_full_cpu(smp_processor_id()) && | |
2970 | (!rcu_gp_in_progress(rsp) || | |
7d0ae808 | 2971 | ULONG_CMP_LT(jiffies, READ_ONCE(rsp->gp_start) + HZ))) |
5ce035fb | 2972 | return true; |
a096932f | 2973 | #endif /* #ifdef CONFIG_NO_HZ_FULL */ |
5ce035fb | 2974 | return false; |
a096932f | 2975 | } |
5057f55e PM |
2976 | |
2977 | /* | |
2978 | * Bind the grace-period kthread for the sysidle flavor of RCU to the | |
2979 | * timekeeping CPU. | |
2980 | */ | |
2981 | static void rcu_bind_gp_kthread(void) | |
2982 | { | |
c0f489d2 | 2983 | int __maybe_unused cpu; |
5057f55e | 2984 | |
c0f489d2 | 2985 | if (!tick_nohz_full_enabled()) |
5057f55e | 2986 | return; |
c0f489d2 PM |
2987 | #ifdef CONFIG_NO_HZ_FULL_SYSIDLE |
2988 | cpu = tick_do_timer_cpu; | |
5871968d | 2989 | if (cpu >= 0 && cpu < nr_cpu_ids) |
5057f55e | 2990 | set_cpus_allowed_ptr(current, cpumask_of(cpu)); |
c0f489d2 | 2991 | #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ |
5871968d | 2992 | housekeeping_affine(current); |
c0f489d2 | 2993 | #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ |
5057f55e | 2994 | } |
176f8f7a PM |
2995 | |
2996 | /* Record the current task on dyntick-idle entry. */ | |
2997 | static void rcu_dynticks_task_enter(void) | |
2998 | { | |
2999 | #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) | |
7d0ae808 | 3000 | WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id()); |
176f8f7a PM |
3001 | #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ |
3002 | } | |
3003 | ||
3004 | /* Record no current task on dyntick-idle exit. */ | |
3005 | static void rcu_dynticks_task_exit(void) | |
3006 | { | |
3007 | #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) | |
7d0ae808 | 3008 | WRITE_ONCE(current->rcu_tasks_idle_cpu, -1); |
176f8f7a PM |
3009 | #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ |
3010 | } |