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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 | |
17 | * along with this program; if not, write to the Free Software | |
18 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. | |
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> |
0edd1b17 | 31 | #include "time/tick-internal.h" |
f41d911f | 32 | |
5b61b0ba MG |
33 | #define RCU_KTHREAD_PRIO 1 |
34 | ||
35 | #ifdef CONFIG_RCU_BOOST | |
36 | #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO | |
37 | #else | |
38 | #define RCU_BOOST_PRIO RCU_KTHREAD_PRIO | |
39 | #endif | |
40 | ||
3fbfbf7a PM |
41 | #ifdef CONFIG_RCU_NOCB_CPU |
42 | static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ | |
43 | static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */ | |
1b0048a4 | 44 | static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ |
3fbfbf7a PM |
45 | static char __initdata nocb_buf[NR_CPUS * 5]; |
46 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ | |
47 | ||
26845c28 PM |
48 | /* |
49 | * Check the RCU kernel configuration parameters and print informative | |
50 | * messages about anything out of the ordinary. If you like #ifdef, you | |
51 | * will love this function. | |
52 | */ | |
53 | static void __init rcu_bootup_announce_oddness(void) | |
54 | { | |
55 | #ifdef CONFIG_RCU_TRACE | |
efc151c3 | 56 | pr_info("\tRCU debugfs-based tracing is enabled.\n"); |
26845c28 PM |
57 | #endif |
58 | #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32) | |
efc151c3 | 59 | pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n", |
26845c28 PM |
60 | CONFIG_RCU_FANOUT); |
61 | #endif | |
62 | #ifdef CONFIG_RCU_FANOUT_EXACT | |
efc151c3 | 63 | pr_info("\tHierarchical RCU autobalancing is disabled.\n"); |
26845c28 PM |
64 | #endif |
65 | #ifdef CONFIG_RCU_FAST_NO_HZ | |
efc151c3 | 66 | pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n"); |
26845c28 PM |
67 | #endif |
68 | #ifdef CONFIG_PROVE_RCU | |
efc151c3 | 69 | pr_info("\tRCU lockdep checking is enabled.\n"); |
26845c28 PM |
70 | #endif |
71 | #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE | |
efc151c3 | 72 | pr_info("\tRCU torture testing starts during boot.\n"); |
26845c28 | 73 | #endif |
81a294c4 | 74 | #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE) |
efc151c3 | 75 | pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n"); |
a858af28 PM |
76 | #endif |
77 | #if defined(CONFIG_RCU_CPU_STALL_INFO) | |
efc151c3 | 78 | pr_info("\tAdditional per-CPU info printed with stalls.\n"); |
26845c28 PM |
79 | #endif |
80 | #if NUM_RCU_LVL_4 != 0 | |
efc151c3 | 81 | pr_info("\tFour-level hierarchy is enabled.\n"); |
26845c28 | 82 | #endif |
f885b7f2 | 83 | if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF) |
9a5739d7 | 84 | pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf); |
cca6f393 | 85 | if (nr_cpu_ids != NR_CPUS) |
efc151c3 | 86 | pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids); |
3fbfbf7a | 87 | #ifdef CONFIG_RCU_NOCB_CPU |
911af505 PM |
88 | #ifndef CONFIG_RCU_NOCB_CPU_NONE |
89 | if (!have_rcu_nocb_mask) { | |
615ee544 | 90 | zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL); |
911af505 PM |
91 | have_rcu_nocb_mask = true; |
92 | } | |
93 | #ifdef CONFIG_RCU_NOCB_CPU_ZERO | |
9a5739d7 | 94 | pr_info("\tOffload RCU callbacks from CPU 0\n"); |
911af505 PM |
95 | cpumask_set_cpu(0, rcu_nocb_mask); |
96 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */ | |
97 | #ifdef CONFIG_RCU_NOCB_CPU_ALL | |
9a5739d7 | 98 | pr_info("\tOffload RCU callbacks from all CPUs\n"); |
911af505 PM |
99 | cpumask_setall(rcu_nocb_mask); |
100 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */ | |
101 | #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */ | |
3fbfbf7a | 102 | if (have_rcu_nocb_mask) { |
3fbfbf7a | 103 | cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask); |
9a5739d7 | 104 | pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf); |
3fbfbf7a | 105 | if (rcu_nocb_poll) |
9a5739d7 | 106 | pr_info("\tPoll for callbacks from no-CBs CPUs.\n"); |
3fbfbf7a PM |
107 | } |
108 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ | |
26845c28 PM |
109 | } |
110 | ||
f41d911f PM |
111 | #ifdef CONFIG_TREE_PREEMPT_RCU |
112 | ||
a41bfeb2 | 113 | RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu); |
27f4d280 | 114 | static struct rcu_state *rcu_state = &rcu_preempt_state; |
f41d911f | 115 | |
d9a3da06 PM |
116 | static int rcu_preempted_readers_exp(struct rcu_node *rnp); |
117 | ||
f41d911f PM |
118 | /* |
119 | * Tell them what RCU they are running. | |
120 | */ | |
0e0fc1c2 | 121 | static void __init rcu_bootup_announce(void) |
f41d911f | 122 | { |
efc151c3 | 123 | pr_info("Preemptible hierarchical RCU implementation.\n"); |
26845c28 | 124 | rcu_bootup_announce_oddness(); |
f41d911f PM |
125 | } |
126 | ||
127 | /* | |
128 | * Return the number of RCU-preempt batches processed thus far | |
129 | * for debug and statistics. | |
130 | */ | |
131 | long rcu_batches_completed_preempt(void) | |
132 | { | |
133 | return rcu_preempt_state.completed; | |
134 | } | |
135 | EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt); | |
136 | ||
137 | /* | |
138 | * Return the number of RCU batches processed thus far for debug & stats. | |
139 | */ | |
140 | long rcu_batches_completed(void) | |
141 | { | |
142 | return rcu_batches_completed_preempt(); | |
143 | } | |
144 | EXPORT_SYMBOL_GPL(rcu_batches_completed); | |
145 | ||
bf66f18e PM |
146 | /* |
147 | * Force a quiescent state for preemptible RCU. | |
148 | */ | |
149 | void rcu_force_quiescent_state(void) | |
150 | { | |
4cdfc175 | 151 | force_quiescent_state(&rcu_preempt_state); |
bf66f18e PM |
152 | } |
153 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); | |
154 | ||
f41d911f | 155 | /* |
6cc68793 | 156 | * Record a preemptible-RCU quiescent state for the specified CPU. Note |
f41d911f PM |
157 | * that this just means that the task currently running on the CPU is |
158 | * not in a quiescent state. There might be any number of tasks blocked | |
159 | * while in an RCU read-side critical section. | |
25502a6c PM |
160 | * |
161 | * Unlike the other rcu_*_qs() functions, callers to this function | |
162 | * must disable irqs in order to protect the assignment to | |
163 | * ->rcu_read_unlock_special. | |
f41d911f | 164 | */ |
c3422bea | 165 | static void rcu_preempt_qs(int cpu) |
f41d911f PM |
166 | { |
167 | struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); | |
25502a6c | 168 | |
e4cc1f22 | 169 | if (rdp->passed_quiesce == 0) |
f7f7bac9 | 170 | trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs")); |
e4cc1f22 | 171 | rdp->passed_quiesce = 1; |
25502a6c | 172 | current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; |
f41d911f PM |
173 | } |
174 | ||
175 | /* | |
c3422bea PM |
176 | * We have entered the scheduler, and the current task might soon be |
177 | * context-switched away from. If this task is in an RCU read-side | |
178 | * critical section, we will no longer be able to rely on the CPU to | |
12f5f524 PM |
179 | * record that fact, so we enqueue the task on the blkd_tasks list. |
180 | * The task will dequeue itself when it exits the outermost enclosing | |
181 | * RCU read-side critical section. Therefore, the current grace period | |
182 | * cannot be permitted to complete until the blkd_tasks list entries | |
183 | * predating the current grace period drain, in other words, until | |
184 | * rnp->gp_tasks becomes NULL. | |
c3422bea PM |
185 | * |
186 | * Caller must disable preemption. | |
f41d911f | 187 | */ |
cba6d0d6 | 188 | static void rcu_preempt_note_context_switch(int cpu) |
f41d911f PM |
189 | { |
190 | struct task_struct *t = current; | |
c3422bea | 191 | unsigned long flags; |
f41d911f PM |
192 | struct rcu_data *rdp; |
193 | struct rcu_node *rnp; | |
194 | ||
10f39bb1 | 195 | if (t->rcu_read_lock_nesting > 0 && |
f41d911f PM |
196 | (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { |
197 | ||
198 | /* Possibly blocking in an RCU read-side critical section. */ | |
cba6d0d6 | 199 | rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu); |
f41d911f | 200 | rnp = rdp->mynode; |
1304afb2 | 201 | raw_spin_lock_irqsave(&rnp->lock, flags); |
f41d911f | 202 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; |
86848966 | 203 | t->rcu_blocked_node = rnp; |
f41d911f PM |
204 | |
205 | /* | |
206 | * If this CPU has already checked in, then this task | |
207 | * will hold up the next grace period rather than the | |
208 | * current grace period. Queue the task accordingly. | |
209 | * If the task is queued for the current grace period | |
210 | * (i.e., this CPU has not yet passed through a quiescent | |
211 | * state for the current grace period), then as long | |
212 | * as that task remains queued, the current grace period | |
12f5f524 PM |
213 | * cannot end. Note that there is some uncertainty as |
214 | * to exactly when the current grace period started. | |
215 | * We take a conservative approach, which can result | |
216 | * in unnecessarily waiting on tasks that started very | |
217 | * slightly after the current grace period began. C'est | |
218 | * la vie!!! | |
b0e165c0 PM |
219 | * |
220 | * But first, note that the current CPU must still be | |
221 | * on line! | |
f41d911f | 222 | */ |
b0e165c0 | 223 | WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); |
e7d8842e | 224 | WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); |
12f5f524 PM |
225 | if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) { |
226 | list_add(&t->rcu_node_entry, rnp->gp_tasks->prev); | |
227 | rnp->gp_tasks = &t->rcu_node_entry; | |
27f4d280 PM |
228 | #ifdef CONFIG_RCU_BOOST |
229 | if (rnp->boost_tasks != NULL) | |
230 | rnp->boost_tasks = rnp->gp_tasks; | |
231 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
12f5f524 PM |
232 | } else { |
233 | list_add(&t->rcu_node_entry, &rnp->blkd_tasks); | |
234 | if (rnp->qsmask & rdp->grpmask) | |
235 | rnp->gp_tasks = &t->rcu_node_entry; | |
236 | } | |
d4c08f2a PM |
237 | trace_rcu_preempt_task(rdp->rsp->name, |
238 | t->pid, | |
239 | (rnp->qsmask & rdp->grpmask) | |
240 | ? rnp->gpnum | |
241 | : rnp->gpnum + 1); | |
1304afb2 | 242 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
10f39bb1 PM |
243 | } else if (t->rcu_read_lock_nesting < 0 && |
244 | t->rcu_read_unlock_special) { | |
245 | ||
246 | /* | |
247 | * Complete exit from RCU read-side critical section on | |
248 | * behalf of preempted instance of __rcu_read_unlock(). | |
249 | */ | |
250 | rcu_read_unlock_special(t); | |
f41d911f PM |
251 | } |
252 | ||
253 | /* | |
254 | * Either we were not in an RCU read-side critical section to | |
255 | * begin with, or we have now recorded that critical section | |
256 | * globally. Either way, we can now note a quiescent state | |
257 | * for this CPU. Again, if we were in an RCU read-side critical | |
258 | * section, and if that critical section was blocking the current | |
259 | * grace period, then the fact that the task has been enqueued | |
260 | * means that we continue to block the current grace period. | |
261 | */ | |
e7d8842e | 262 | local_irq_save(flags); |
cba6d0d6 | 263 | rcu_preempt_qs(cpu); |
e7d8842e | 264 | local_irq_restore(flags); |
f41d911f PM |
265 | } |
266 | ||
fc2219d4 PM |
267 | /* |
268 | * Check for preempted RCU readers blocking the current grace period | |
269 | * for the specified rcu_node structure. If the caller needs a reliable | |
270 | * answer, it must hold the rcu_node's ->lock. | |
271 | */ | |
27f4d280 | 272 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 | 273 | { |
12f5f524 | 274 | return rnp->gp_tasks != NULL; |
fc2219d4 PM |
275 | } |
276 | ||
b668c9cf PM |
277 | /* |
278 | * Record a quiescent state for all tasks that were previously queued | |
279 | * on the specified rcu_node structure and that were blocking the current | |
280 | * RCU grace period. The caller must hold the specified rnp->lock with | |
281 | * irqs disabled, and this lock is released upon return, but irqs remain | |
282 | * disabled. | |
283 | */ | |
d3f6bad3 | 284 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
b668c9cf PM |
285 | __releases(rnp->lock) |
286 | { | |
287 | unsigned long mask; | |
288 | struct rcu_node *rnp_p; | |
289 | ||
27f4d280 | 290 | if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { |
1304afb2 | 291 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b668c9cf PM |
292 | return; /* Still need more quiescent states! */ |
293 | } | |
294 | ||
295 | rnp_p = rnp->parent; | |
296 | if (rnp_p == NULL) { | |
297 | /* | |
298 | * Either there is only one rcu_node in the tree, | |
299 | * or tasks were kicked up to root rcu_node due to | |
300 | * CPUs going offline. | |
301 | */ | |
d3f6bad3 | 302 | rcu_report_qs_rsp(&rcu_preempt_state, flags); |
b668c9cf PM |
303 | return; |
304 | } | |
305 | ||
306 | /* Report up the rest of the hierarchy. */ | |
307 | mask = rnp->grpmask; | |
1304afb2 PM |
308 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
309 | raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */ | |
d3f6bad3 | 310 | rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags); |
b668c9cf PM |
311 | } |
312 | ||
12f5f524 PM |
313 | /* |
314 | * Advance a ->blkd_tasks-list pointer to the next entry, instead | |
315 | * returning NULL if at the end of the list. | |
316 | */ | |
317 | static struct list_head *rcu_next_node_entry(struct task_struct *t, | |
318 | struct rcu_node *rnp) | |
319 | { | |
320 | struct list_head *np; | |
321 | ||
322 | np = t->rcu_node_entry.next; | |
323 | if (np == &rnp->blkd_tasks) | |
324 | np = NULL; | |
325 | return np; | |
326 | } | |
327 | ||
b668c9cf PM |
328 | /* |
329 | * Handle special cases during rcu_read_unlock(), such as needing to | |
330 | * notify RCU core processing or task having blocked during the RCU | |
331 | * read-side critical section. | |
332 | */ | |
2a3fa843 | 333 | void rcu_read_unlock_special(struct task_struct *t) |
f41d911f PM |
334 | { |
335 | int empty; | |
d9a3da06 | 336 | int empty_exp; |
389abd48 | 337 | int empty_exp_now; |
f41d911f | 338 | unsigned long flags; |
12f5f524 | 339 | struct list_head *np; |
82e78d80 PM |
340 | #ifdef CONFIG_RCU_BOOST |
341 | struct rt_mutex *rbmp = NULL; | |
342 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
f41d911f PM |
343 | struct rcu_node *rnp; |
344 | int special; | |
345 | ||
346 | /* NMI handlers cannot block and cannot safely manipulate state. */ | |
347 | if (in_nmi()) | |
348 | return; | |
349 | ||
350 | local_irq_save(flags); | |
351 | ||
352 | /* | |
353 | * If RCU core is waiting for this CPU to exit critical section, | |
354 | * let it know that we have done so. | |
355 | */ | |
356 | special = t->rcu_read_unlock_special; | |
357 | if (special & RCU_READ_UNLOCK_NEED_QS) { | |
c3422bea | 358 | rcu_preempt_qs(smp_processor_id()); |
f41d911f PM |
359 | } |
360 | ||
361 | /* Hardware IRQ handlers cannot block. */ | |
ec433f0c | 362 | if (in_irq() || in_serving_softirq()) { |
f41d911f PM |
363 | local_irq_restore(flags); |
364 | return; | |
365 | } | |
366 | ||
367 | /* Clean up if blocked during RCU read-side critical section. */ | |
368 | if (special & RCU_READ_UNLOCK_BLOCKED) { | |
369 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; | |
370 | ||
dd5d19ba PM |
371 | /* |
372 | * Remove this task from the list it blocked on. The | |
373 | * task can migrate while we acquire the lock, but at | |
374 | * most one time. So at most two passes through loop. | |
375 | */ | |
376 | for (;;) { | |
86848966 | 377 | rnp = t->rcu_blocked_node; |
1304afb2 | 378 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
86848966 | 379 | if (rnp == t->rcu_blocked_node) |
dd5d19ba | 380 | break; |
1304afb2 | 381 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
dd5d19ba | 382 | } |
27f4d280 | 383 | empty = !rcu_preempt_blocked_readers_cgp(rnp); |
d9a3da06 PM |
384 | empty_exp = !rcu_preempted_readers_exp(rnp); |
385 | smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ | |
12f5f524 | 386 | np = rcu_next_node_entry(t, rnp); |
f41d911f | 387 | list_del_init(&t->rcu_node_entry); |
82e78d80 | 388 | t->rcu_blocked_node = NULL; |
f7f7bac9 | 389 | trace_rcu_unlock_preempted_task(TPS("rcu_preempt"), |
d4c08f2a | 390 | rnp->gpnum, t->pid); |
12f5f524 PM |
391 | if (&t->rcu_node_entry == rnp->gp_tasks) |
392 | rnp->gp_tasks = np; | |
393 | if (&t->rcu_node_entry == rnp->exp_tasks) | |
394 | rnp->exp_tasks = np; | |
27f4d280 PM |
395 | #ifdef CONFIG_RCU_BOOST |
396 | if (&t->rcu_node_entry == rnp->boost_tasks) | |
397 | rnp->boost_tasks = np; | |
82e78d80 PM |
398 | /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */ |
399 | if (t->rcu_boost_mutex) { | |
400 | rbmp = t->rcu_boost_mutex; | |
401 | t->rcu_boost_mutex = NULL; | |
7765be2f | 402 | } |
27f4d280 | 403 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
f41d911f PM |
404 | |
405 | /* | |
406 | * If this was the last task on the current list, and if | |
407 | * we aren't waiting on any CPUs, report the quiescent state. | |
389abd48 PM |
408 | * Note that rcu_report_unblock_qs_rnp() releases rnp->lock, |
409 | * so we must take a snapshot of the expedited state. | |
f41d911f | 410 | */ |
389abd48 | 411 | empty_exp_now = !rcu_preempted_readers_exp(rnp); |
d4c08f2a | 412 | if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) { |
f7f7bac9 | 413 | trace_rcu_quiescent_state_report(TPS("preempt_rcu"), |
d4c08f2a PM |
414 | rnp->gpnum, |
415 | 0, rnp->qsmask, | |
416 | rnp->level, | |
417 | rnp->grplo, | |
418 | rnp->grphi, | |
419 | !!rnp->gp_tasks); | |
d3f6bad3 | 420 | rcu_report_unblock_qs_rnp(rnp, flags); |
c701d5d9 | 421 | } else { |
d4c08f2a | 422 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
c701d5d9 | 423 | } |
d9a3da06 | 424 | |
27f4d280 PM |
425 | #ifdef CONFIG_RCU_BOOST |
426 | /* Unboost if we were boosted. */ | |
82e78d80 PM |
427 | if (rbmp) |
428 | rt_mutex_unlock(rbmp); | |
27f4d280 PM |
429 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
430 | ||
d9a3da06 PM |
431 | /* |
432 | * If this was the last task on the expedited lists, | |
433 | * then we need to report up the rcu_node hierarchy. | |
434 | */ | |
389abd48 | 435 | if (!empty_exp && empty_exp_now) |
b40d293e | 436 | rcu_report_exp_rnp(&rcu_preempt_state, rnp, true); |
b668c9cf PM |
437 | } else { |
438 | local_irq_restore(flags); | |
f41d911f | 439 | } |
f41d911f PM |
440 | } |
441 | ||
1ed509a2 PM |
442 | #ifdef CONFIG_RCU_CPU_STALL_VERBOSE |
443 | ||
444 | /* | |
445 | * Dump detailed information for all tasks blocking the current RCU | |
446 | * grace period on the specified rcu_node structure. | |
447 | */ | |
448 | static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) | |
449 | { | |
450 | unsigned long flags; | |
1ed509a2 PM |
451 | struct task_struct *t; |
452 | ||
12f5f524 | 453 | raw_spin_lock_irqsave(&rnp->lock, flags); |
5fd4dc06 PM |
454 | if (!rcu_preempt_blocked_readers_cgp(rnp)) { |
455 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
456 | return; | |
457 | } | |
12f5f524 PM |
458 | t = list_entry(rnp->gp_tasks, |
459 | struct task_struct, rcu_node_entry); | |
460 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) | |
461 | sched_show_task(t); | |
462 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
1ed509a2 PM |
463 | } |
464 | ||
465 | /* | |
466 | * Dump detailed information for all tasks blocking the current RCU | |
467 | * grace period. | |
468 | */ | |
469 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
470 | { | |
471 | struct rcu_node *rnp = rcu_get_root(rsp); | |
472 | ||
473 | rcu_print_detail_task_stall_rnp(rnp); | |
474 | rcu_for_each_leaf_node(rsp, rnp) | |
475 | rcu_print_detail_task_stall_rnp(rnp); | |
476 | } | |
477 | ||
478 | #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ | |
479 | ||
480 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
481 | { | |
482 | } | |
483 | ||
484 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ | |
485 | ||
a858af28 PM |
486 | #ifdef CONFIG_RCU_CPU_STALL_INFO |
487 | ||
488 | static void rcu_print_task_stall_begin(struct rcu_node *rnp) | |
489 | { | |
efc151c3 | 490 | pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", |
a858af28 PM |
491 | rnp->level, rnp->grplo, rnp->grphi); |
492 | } | |
493 | ||
494 | static void rcu_print_task_stall_end(void) | |
495 | { | |
efc151c3 | 496 | pr_cont("\n"); |
a858af28 PM |
497 | } |
498 | ||
499 | #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ | |
500 | ||
501 | static void rcu_print_task_stall_begin(struct rcu_node *rnp) | |
502 | { | |
503 | } | |
504 | ||
505 | static void rcu_print_task_stall_end(void) | |
506 | { | |
507 | } | |
508 | ||
509 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ | |
510 | ||
f41d911f PM |
511 | /* |
512 | * Scan the current list of tasks blocked within RCU read-side critical | |
513 | * sections, printing out the tid of each. | |
514 | */ | |
9bc8b558 | 515 | static int rcu_print_task_stall(struct rcu_node *rnp) |
f41d911f | 516 | { |
f41d911f | 517 | struct task_struct *t; |
9bc8b558 | 518 | int ndetected = 0; |
f41d911f | 519 | |
27f4d280 | 520 | if (!rcu_preempt_blocked_readers_cgp(rnp)) |
9bc8b558 | 521 | return 0; |
a858af28 | 522 | rcu_print_task_stall_begin(rnp); |
12f5f524 PM |
523 | t = list_entry(rnp->gp_tasks, |
524 | struct task_struct, rcu_node_entry); | |
9bc8b558 | 525 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { |
efc151c3 | 526 | pr_cont(" P%d", t->pid); |
9bc8b558 PM |
527 | ndetected++; |
528 | } | |
a858af28 | 529 | rcu_print_task_stall_end(); |
9bc8b558 | 530 | return ndetected; |
f41d911f PM |
531 | } |
532 | ||
b0e165c0 PM |
533 | /* |
534 | * Check that the list of blocked tasks for the newly completed grace | |
535 | * period is in fact empty. It is a serious bug to complete a grace | |
536 | * period that still has RCU readers blocked! This function must be | |
537 | * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock | |
538 | * must be held by the caller. | |
12f5f524 PM |
539 | * |
540 | * Also, if there are blocked tasks on the list, they automatically | |
541 | * block the newly created grace period, so set up ->gp_tasks accordingly. | |
b0e165c0 PM |
542 | */ |
543 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
544 | { | |
27f4d280 | 545 | WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); |
12f5f524 PM |
546 | if (!list_empty(&rnp->blkd_tasks)) |
547 | rnp->gp_tasks = rnp->blkd_tasks.next; | |
28ecd580 | 548 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
549 | } |
550 | ||
33f76148 PM |
551 | #ifdef CONFIG_HOTPLUG_CPU |
552 | ||
dd5d19ba PM |
553 | /* |
554 | * Handle tasklist migration for case in which all CPUs covered by the | |
555 | * specified rcu_node have gone offline. Move them up to the root | |
556 | * rcu_node. The reason for not just moving them to the immediate | |
557 | * parent is to remove the need for rcu_read_unlock_special() to | |
558 | * make more than two attempts to acquire the target rcu_node's lock. | |
b668c9cf PM |
559 | * Returns true if there were tasks blocking the current RCU grace |
560 | * period. | |
dd5d19ba | 561 | * |
237c80c5 PM |
562 | * Returns 1 if there was previously a task blocking the current grace |
563 | * period on the specified rcu_node structure. | |
564 | * | |
dd5d19ba PM |
565 | * The caller must hold rnp->lock with irqs disabled. |
566 | */ | |
237c80c5 PM |
567 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
568 | struct rcu_node *rnp, | |
569 | struct rcu_data *rdp) | |
dd5d19ba | 570 | { |
dd5d19ba PM |
571 | struct list_head *lp; |
572 | struct list_head *lp_root; | |
d9a3da06 | 573 | int retval = 0; |
dd5d19ba | 574 | struct rcu_node *rnp_root = rcu_get_root(rsp); |
12f5f524 | 575 | struct task_struct *t; |
dd5d19ba | 576 | |
86848966 PM |
577 | if (rnp == rnp_root) { |
578 | WARN_ONCE(1, "Last CPU thought to be offlined?"); | |
237c80c5 | 579 | return 0; /* Shouldn't happen: at least one CPU online. */ |
86848966 | 580 | } |
12f5f524 PM |
581 | |
582 | /* If we are on an internal node, complain bitterly. */ | |
583 | WARN_ON_ONCE(rnp != rdp->mynode); | |
dd5d19ba PM |
584 | |
585 | /* | |
12f5f524 PM |
586 | * Move tasks up to root rcu_node. Don't try to get fancy for |
587 | * this corner-case operation -- just put this node's tasks | |
588 | * at the head of the root node's list, and update the root node's | |
589 | * ->gp_tasks and ->exp_tasks pointers to those of this node's, | |
590 | * if non-NULL. This might result in waiting for more tasks than | |
591 | * absolutely necessary, but this is a good performance/complexity | |
592 | * tradeoff. | |
dd5d19ba | 593 | */ |
2036d94a | 594 | if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0) |
d9a3da06 PM |
595 | retval |= RCU_OFL_TASKS_NORM_GP; |
596 | if (rcu_preempted_readers_exp(rnp)) | |
597 | retval |= RCU_OFL_TASKS_EXP_GP; | |
12f5f524 PM |
598 | lp = &rnp->blkd_tasks; |
599 | lp_root = &rnp_root->blkd_tasks; | |
600 | while (!list_empty(lp)) { | |
601 | t = list_entry(lp->next, typeof(*t), rcu_node_entry); | |
602 | raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ | |
603 | list_del(&t->rcu_node_entry); | |
604 | t->rcu_blocked_node = rnp_root; | |
605 | list_add(&t->rcu_node_entry, lp_root); | |
606 | if (&t->rcu_node_entry == rnp->gp_tasks) | |
607 | rnp_root->gp_tasks = rnp->gp_tasks; | |
608 | if (&t->rcu_node_entry == rnp->exp_tasks) | |
609 | rnp_root->exp_tasks = rnp->exp_tasks; | |
27f4d280 PM |
610 | #ifdef CONFIG_RCU_BOOST |
611 | if (&t->rcu_node_entry == rnp->boost_tasks) | |
612 | rnp_root->boost_tasks = rnp->boost_tasks; | |
613 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
12f5f524 | 614 | raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ |
dd5d19ba | 615 | } |
27f4d280 | 616 | |
1e3fd2b3 PM |
617 | rnp->gp_tasks = NULL; |
618 | rnp->exp_tasks = NULL; | |
27f4d280 | 619 | #ifdef CONFIG_RCU_BOOST |
1e3fd2b3 | 620 | rnp->boost_tasks = NULL; |
5cc900cf PM |
621 | /* |
622 | * In case root is being boosted and leaf was not. Make sure | |
623 | * that we boost the tasks blocking the current grace period | |
624 | * in this case. | |
625 | */ | |
27f4d280 PM |
626 | raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ |
627 | if (rnp_root->boost_tasks != NULL && | |
5cc900cf PM |
628 | rnp_root->boost_tasks != rnp_root->gp_tasks && |
629 | rnp_root->boost_tasks != rnp_root->exp_tasks) | |
27f4d280 PM |
630 | rnp_root->boost_tasks = rnp_root->gp_tasks; |
631 | raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ | |
632 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
633 | ||
237c80c5 | 634 | return retval; |
dd5d19ba PM |
635 | } |
636 | ||
e5601400 PM |
637 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
638 | ||
f41d911f PM |
639 | /* |
640 | * Check for a quiescent state from the current CPU. When a task blocks, | |
641 | * the task is recorded in the corresponding CPU's rcu_node structure, | |
642 | * which is checked elsewhere. | |
643 | * | |
644 | * Caller must disable hard irqs. | |
645 | */ | |
646 | static void rcu_preempt_check_callbacks(int cpu) | |
647 | { | |
648 | struct task_struct *t = current; | |
649 | ||
650 | if (t->rcu_read_lock_nesting == 0) { | |
c3422bea | 651 | rcu_preempt_qs(cpu); |
f41d911f PM |
652 | return; |
653 | } | |
10f39bb1 PM |
654 | if (t->rcu_read_lock_nesting > 0 && |
655 | per_cpu(rcu_preempt_data, cpu).qs_pending) | |
c3422bea | 656 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; |
f41d911f PM |
657 | } |
658 | ||
a46e0899 PM |
659 | #ifdef CONFIG_RCU_BOOST |
660 | ||
09223371 SL |
661 | static void rcu_preempt_do_callbacks(void) |
662 | { | |
663 | rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data)); | |
664 | } | |
665 | ||
a46e0899 PM |
666 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
667 | ||
f41d911f | 668 | /* |
6cc68793 | 669 | * Queue a preemptible-RCU callback for invocation after a grace period. |
f41d911f PM |
670 | */ |
671 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) | |
672 | { | |
3fbfbf7a | 673 | __call_rcu(head, func, &rcu_preempt_state, -1, 0); |
f41d911f PM |
674 | } |
675 | EXPORT_SYMBOL_GPL(call_rcu); | |
676 | ||
486e2593 PM |
677 | /* |
678 | * Queue an RCU callback for lazy invocation after a grace period. | |
679 | * This will likely be later named something like "call_rcu_lazy()", | |
680 | * but this change will require some way of tagging the lazy RCU | |
681 | * callbacks in the list of pending callbacks. Until then, this | |
682 | * function may only be called from __kfree_rcu(). | |
683 | */ | |
684 | void kfree_call_rcu(struct rcu_head *head, | |
685 | void (*func)(struct rcu_head *rcu)) | |
686 | { | |
3fbfbf7a | 687 | __call_rcu(head, func, &rcu_preempt_state, -1, 1); |
486e2593 PM |
688 | } |
689 | EXPORT_SYMBOL_GPL(kfree_call_rcu); | |
690 | ||
6ebb237b PM |
691 | /** |
692 | * synchronize_rcu - wait until a grace period has elapsed. | |
693 | * | |
694 | * Control will return to the caller some time after a full grace | |
695 | * period has elapsed, in other words after all currently executing RCU | |
77d8485a PM |
696 | * read-side critical sections have completed. Note, however, that |
697 | * upon return from synchronize_rcu(), the caller might well be executing | |
698 | * concurrently with new RCU read-side critical sections that began while | |
699 | * synchronize_rcu() was waiting. RCU read-side critical sections are | |
700 | * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. | |
f0a0e6f2 PM |
701 | * |
702 | * See the description of synchronize_sched() for more detailed information | |
703 | * on memory ordering guarantees. | |
6ebb237b PM |
704 | */ |
705 | void synchronize_rcu(void) | |
706 | { | |
fe15d706 PM |
707 | rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && |
708 | !lock_is_held(&rcu_lock_map) && | |
709 | !lock_is_held(&rcu_sched_lock_map), | |
710 | "Illegal synchronize_rcu() in RCU read-side critical section"); | |
6ebb237b PM |
711 | if (!rcu_scheduler_active) |
712 | return; | |
3705b88d AM |
713 | if (rcu_expedited) |
714 | synchronize_rcu_expedited(); | |
715 | else | |
716 | wait_rcu_gp(call_rcu); | |
6ebb237b PM |
717 | } |
718 | EXPORT_SYMBOL_GPL(synchronize_rcu); | |
719 | ||
d9a3da06 | 720 | static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); |
bcfa57ce | 721 | static unsigned long sync_rcu_preempt_exp_count; |
d9a3da06 PM |
722 | static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); |
723 | ||
724 | /* | |
725 | * Return non-zero if there are any tasks in RCU read-side critical | |
726 | * sections blocking the current preemptible-RCU expedited grace period. | |
727 | * If there is no preemptible-RCU expedited grace period currently in | |
728 | * progress, returns zero unconditionally. | |
729 | */ | |
730 | static int rcu_preempted_readers_exp(struct rcu_node *rnp) | |
731 | { | |
12f5f524 | 732 | return rnp->exp_tasks != NULL; |
d9a3da06 PM |
733 | } |
734 | ||
735 | /* | |
736 | * return non-zero if there is no RCU expedited grace period in progress | |
737 | * for the specified rcu_node structure, in other words, if all CPUs and | |
738 | * tasks covered by the specified rcu_node structure have done their bit | |
739 | * for the current expedited grace period. Works only for preemptible | |
740 | * RCU -- other RCU implementation use other means. | |
741 | * | |
742 | * Caller must hold sync_rcu_preempt_exp_mutex. | |
743 | */ | |
744 | static int sync_rcu_preempt_exp_done(struct rcu_node *rnp) | |
745 | { | |
746 | return !rcu_preempted_readers_exp(rnp) && | |
747 | ACCESS_ONCE(rnp->expmask) == 0; | |
748 | } | |
749 | ||
750 | /* | |
751 | * Report the exit from RCU read-side critical section for the last task | |
752 | * that queued itself during or before the current expedited preemptible-RCU | |
753 | * grace period. This event is reported either to the rcu_node structure on | |
754 | * which the task was queued or to one of that rcu_node structure's ancestors, | |
755 | * recursively up the tree. (Calm down, calm down, we do the recursion | |
756 | * iteratively!) | |
757 | * | |
b40d293e TG |
758 | * Most callers will set the "wake" flag, but the task initiating the |
759 | * expedited grace period need not wake itself. | |
760 | * | |
d9a3da06 PM |
761 | * Caller must hold sync_rcu_preempt_exp_mutex. |
762 | */ | |
b40d293e TG |
763 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, |
764 | bool wake) | |
d9a3da06 PM |
765 | { |
766 | unsigned long flags; | |
767 | unsigned long mask; | |
768 | ||
1304afb2 | 769 | raw_spin_lock_irqsave(&rnp->lock, flags); |
d9a3da06 | 770 | for (;;) { |
131906b0 PM |
771 | if (!sync_rcu_preempt_exp_done(rnp)) { |
772 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
d9a3da06 | 773 | break; |
131906b0 | 774 | } |
d9a3da06 | 775 | if (rnp->parent == NULL) { |
131906b0 | 776 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b40d293e TG |
777 | if (wake) |
778 | wake_up(&sync_rcu_preempt_exp_wq); | |
d9a3da06 PM |
779 | break; |
780 | } | |
781 | mask = rnp->grpmask; | |
1304afb2 | 782 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ |
d9a3da06 | 783 | rnp = rnp->parent; |
1304afb2 | 784 | raw_spin_lock(&rnp->lock); /* irqs already disabled */ |
d9a3da06 PM |
785 | rnp->expmask &= ~mask; |
786 | } | |
d9a3da06 PM |
787 | } |
788 | ||
789 | /* | |
790 | * Snapshot the tasks blocking the newly started preemptible-RCU expedited | |
791 | * grace period for the specified rcu_node structure. If there are no such | |
792 | * tasks, report it up the rcu_node hierarchy. | |
793 | * | |
7b2e6011 PM |
794 | * Caller must hold sync_rcu_preempt_exp_mutex and must exclude |
795 | * CPU hotplug operations. | |
d9a3da06 PM |
796 | */ |
797 | static void | |
798 | sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) | |
799 | { | |
1217ed1b | 800 | unsigned long flags; |
12f5f524 | 801 | int must_wait = 0; |
d9a3da06 | 802 | |
1217ed1b | 803 | raw_spin_lock_irqsave(&rnp->lock, flags); |
c701d5d9 | 804 | if (list_empty(&rnp->blkd_tasks)) { |
1217ed1b | 805 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
c701d5d9 | 806 | } else { |
12f5f524 | 807 | rnp->exp_tasks = rnp->blkd_tasks.next; |
1217ed1b | 808 | rcu_initiate_boost(rnp, flags); /* releases rnp->lock */ |
12f5f524 PM |
809 | must_wait = 1; |
810 | } | |
d9a3da06 | 811 | if (!must_wait) |
b40d293e | 812 | rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */ |
d9a3da06 PM |
813 | } |
814 | ||
236fefaf PM |
815 | /** |
816 | * synchronize_rcu_expedited - Brute-force RCU grace period | |
817 | * | |
818 | * Wait for an RCU-preempt grace period, but expedite it. The basic | |
819 | * idea is to invoke synchronize_sched_expedited() to push all the tasks to | |
820 | * the ->blkd_tasks lists and wait for this list to drain. This consumes | |
821 | * significant time on all CPUs and is unfriendly to real-time workloads, | |
822 | * so is thus not recommended for any sort of common-case code. | |
823 | * In fact, if you are using synchronize_rcu_expedited() in a loop, | |
824 | * please restructure your code to batch your updates, and then Use a | |
825 | * single synchronize_rcu() instead. | |
826 | * | |
827 | * Note that it is illegal to call this function while holding any lock | |
828 | * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal | |
829 | * to call this function from a CPU-hotplug notifier. Failing to observe | |
830 | * these restriction will result in deadlock. | |
019129d5 PM |
831 | */ |
832 | void synchronize_rcu_expedited(void) | |
833 | { | |
d9a3da06 PM |
834 | unsigned long flags; |
835 | struct rcu_node *rnp; | |
836 | struct rcu_state *rsp = &rcu_preempt_state; | |
bcfa57ce | 837 | unsigned long snap; |
d9a3da06 PM |
838 | int trycount = 0; |
839 | ||
840 | smp_mb(); /* Caller's modifications seen first by other CPUs. */ | |
841 | snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1; | |
842 | smp_mb(); /* Above access cannot bleed into critical section. */ | |
843 | ||
1943c89d PM |
844 | /* |
845 | * Block CPU-hotplug operations. This means that any CPU-hotplug | |
846 | * operation that finds an rcu_node structure with tasks in the | |
847 | * process of being boosted will know that all tasks blocking | |
848 | * this expedited grace period will already be in the process of | |
849 | * being boosted. This simplifies the process of moving tasks | |
850 | * from leaf to root rcu_node structures. | |
851 | */ | |
852 | get_online_cpus(); | |
853 | ||
d9a3da06 PM |
854 | /* |
855 | * Acquire lock, falling back to synchronize_rcu() if too many | |
856 | * lock-acquisition failures. Of course, if someone does the | |
857 | * expedited grace period for us, just leave. | |
858 | */ | |
859 | while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) { | |
1943c89d PM |
860 | if (ULONG_CMP_LT(snap, |
861 | ACCESS_ONCE(sync_rcu_preempt_exp_count))) { | |
862 | put_online_cpus(); | |
863 | goto mb_ret; /* Others did our work for us. */ | |
864 | } | |
c701d5d9 | 865 | if (trycount++ < 10) { |
d9a3da06 | 866 | udelay(trycount * num_online_cpus()); |
c701d5d9 | 867 | } else { |
1943c89d | 868 | put_online_cpus(); |
3705b88d | 869 | wait_rcu_gp(call_rcu); |
d9a3da06 PM |
870 | return; |
871 | } | |
d9a3da06 | 872 | } |
1943c89d PM |
873 | if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) { |
874 | put_online_cpus(); | |
d9a3da06 | 875 | goto unlock_mb_ret; /* Others did our work for us. */ |
1943c89d | 876 | } |
d9a3da06 | 877 | |
12f5f524 | 878 | /* force all RCU readers onto ->blkd_tasks lists. */ |
d9a3da06 PM |
879 | synchronize_sched_expedited(); |
880 | ||
d9a3da06 PM |
881 | /* Initialize ->expmask for all non-leaf rcu_node structures. */ |
882 | rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) { | |
1943c89d | 883 | raw_spin_lock_irqsave(&rnp->lock, flags); |
d9a3da06 | 884 | rnp->expmask = rnp->qsmaskinit; |
1943c89d | 885 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
d9a3da06 PM |
886 | } |
887 | ||
12f5f524 | 888 | /* Snapshot current state of ->blkd_tasks lists. */ |
d9a3da06 PM |
889 | rcu_for_each_leaf_node(rsp, rnp) |
890 | sync_rcu_preempt_exp_init(rsp, rnp); | |
891 | if (NUM_RCU_NODES > 1) | |
892 | sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp)); | |
893 | ||
1943c89d | 894 | put_online_cpus(); |
d9a3da06 | 895 | |
12f5f524 | 896 | /* Wait for snapshotted ->blkd_tasks lists to drain. */ |
d9a3da06 PM |
897 | rnp = rcu_get_root(rsp); |
898 | wait_event(sync_rcu_preempt_exp_wq, | |
899 | sync_rcu_preempt_exp_done(rnp)); | |
900 | ||
901 | /* Clean up and exit. */ | |
902 | smp_mb(); /* ensure expedited GP seen before counter increment. */ | |
903 | ACCESS_ONCE(sync_rcu_preempt_exp_count)++; | |
904 | unlock_mb_ret: | |
905 | mutex_unlock(&sync_rcu_preempt_exp_mutex); | |
906 | mb_ret: | |
907 | smp_mb(); /* ensure subsequent action seen after grace period. */ | |
019129d5 PM |
908 | } |
909 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
910 | ||
e74f4c45 PM |
911 | /** |
912 | * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. | |
f0a0e6f2 PM |
913 | * |
914 | * Note that this primitive does not necessarily wait for an RCU grace period | |
915 | * to complete. For example, if there are no RCU callbacks queued anywhere | |
916 | * in the system, then rcu_barrier() is within its rights to return | |
917 | * immediately, without waiting for anything, much less an RCU grace period. | |
e74f4c45 PM |
918 | */ |
919 | void rcu_barrier(void) | |
920 | { | |
037b64ed | 921 | _rcu_barrier(&rcu_preempt_state); |
e74f4c45 PM |
922 | } |
923 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
924 | ||
1eba8f84 | 925 | /* |
6cc68793 | 926 | * Initialize preemptible RCU's state structures. |
1eba8f84 PM |
927 | */ |
928 | static void __init __rcu_init_preempt(void) | |
929 | { | |
394f99a9 | 930 | rcu_init_one(&rcu_preempt_state, &rcu_preempt_data); |
1eba8f84 PM |
931 | } |
932 | ||
2439b696 PM |
933 | /* |
934 | * Check for a task exiting while in a preemptible-RCU read-side | |
935 | * critical section, clean up if so. No need to issue warnings, | |
936 | * as debug_check_no_locks_held() already does this if lockdep | |
937 | * is enabled. | |
938 | */ | |
939 | void exit_rcu(void) | |
940 | { | |
941 | struct task_struct *t = current; | |
942 | ||
943 | if (likely(list_empty(¤t->rcu_node_entry))) | |
944 | return; | |
945 | t->rcu_read_lock_nesting = 1; | |
946 | barrier(); | |
947 | t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED; | |
948 | __rcu_read_unlock(); | |
949 | } | |
950 | ||
f41d911f PM |
951 | #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ |
952 | ||
27f4d280 PM |
953 | static struct rcu_state *rcu_state = &rcu_sched_state; |
954 | ||
f41d911f PM |
955 | /* |
956 | * Tell them what RCU they are running. | |
957 | */ | |
0e0fc1c2 | 958 | static void __init rcu_bootup_announce(void) |
f41d911f | 959 | { |
efc151c3 | 960 | pr_info("Hierarchical RCU implementation.\n"); |
26845c28 | 961 | rcu_bootup_announce_oddness(); |
f41d911f PM |
962 | } |
963 | ||
964 | /* | |
965 | * Return the number of RCU batches processed thus far for debug & stats. | |
966 | */ | |
967 | long rcu_batches_completed(void) | |
968 | { | |
969 | return rcu_batches_completed_sched(); | |
970 | } | |
971 | EXPORT_SYMBOL_GPL(rcu_batches_completed); | |
972 | ||
bf66f18e PM |
973 | /* |
974 | * Force a quiescent state for RCU, which, because there is no preemptible | |
975 | * RCU, becomes the same as rcu-sched. | |
976 | */ | |
977 | void rcu_force_quiescent_state(void) | |
978 | { | |
979 | rcu_sched_force_quiescent_state(); | |
980 | } | |
981 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); | |
982 | ||
cba6d0d6 PM |
983 | /* |
984 | * Because preemptible RCU does not exist, we never have to check for | |
985 | * CPUs being in quiescent states. | |
986 | */ | |
987 | static void rcu_preempt_note_context_switch(int cpu) | |
988 | { | |
989 | } | |
990 | ||
fc2219d4 | 991 | /* |
6cc68793 | 992 | * Because preemptible RCU does not exist, there are never any preempted |
fc2219d4 PM |
993 | * RCU readers. |
994 | */ | |
27f4d280 | 995 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 PM |
996 | { |
997 | return 0; | |
998 | } | |
999 | ||
b668c9cf PM |
1000 | #ifdef CONFIG_HOTPLUG_CPU |
1001 | ||
1002 | /* Because preemptible RCU does not exist, no quieting of tasks. */ | |
d3f6bad3 | 1003 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
b668c9cf | 1004 | { |
1304afb2 | 1005 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b668c9cf PM |
1006 | } |
1007 | ||
1008 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
1009 | ||
1ed509a2 | 1010 | /* |
6cc68793 | 1011 | * Because preemptible RCU does not exist, we never have to check for |
1ed509a2 PM |
1012 | * tasks blocked within RCU read-side critical sections. |
1013 | */ | |
1014 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
1015 | { | |
1016 | } | |
1017 | ||
f41d911f | 1018 | /* |
6cc68793 | 1019 | * Because preemptible RCU does not exist, we never have to check for |
f41d911f PM |
1020 | * tasks blocked within RCU read-side critical sections. |
1021 | */ | |
9bc8b558 | 1022 | static int rcu_print_task_stall(struct rcu_node *rnp) |
f41d911f | 1023 | { |
9bc8b558 | 1024 | return 0; |
f41d911f PM |
1025 | } |
1026 | ||
b0e165c0 | 1027 | /* |
6cc68793 | 1028 | * Because there is no preemptible RCU, there can be no readers blocked, |
49e29126 PM |
1029 | * so there is no need to check for blocked tasks. So check only for |
1030 | * bogus qsmask values. | |
b0e165c0 PM |
1031 | */ |
1032 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
1033 | { | |
49e29126 | 1034 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
1035 | } |
1036 | ||
33f76148 PM |
1037 | #ifdef CONFIG_HOTPLUG_CPU |
1038 | ||
dd5d19ba | 1039 | /* |
6cc68793 | 1040 | * Because preemptible RCU does not exist, it never needs to migrate |
237c80c5 PM |
1041 | * tasks that were blocked within RCU read-side critical sections, and |
1042 | * such non-existent tasks cannot possibly have been blocking the current | |
1043 | * grace period. | |
dd5d19ba | 1044 | */ |
237c80c5 PM |
1045 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
1046 | struct rcu_node *rnp, | |
1047 | struct rcu_data *rdp) | |
dd5d19ba | 1048 | { |
237c80c5 | 1049 | return 0; |
dd5d19ba PM |
1050 | } |
1051 | ||
e5601400 PM |
1052 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
1053 | ||
f41d911f | 1054 | /* |
6cc68793 | 1055 | * Because preemptible RCU does not exist, it never has any callbacks |
f41d911f PM |
1056 | * to check. |
1057 | */ | |
1eba8f84 | 1058 | static void rcu_preempt_check_callbacks(int cpu) |
f41d911f PM |
1059 | { |
1060 | } | |
1061 | ||
486e2593 PM |
1062 | /* |
1063 | * Queue an RCU callback for lazy invocation after a grace period. | |
1064 | * This will likely be later named something like "call_rcu_lazy()", | |
1065 | * but this change will require some way of tagging the lazy RCU | |
1066 | * callbacks in the list of pending callbacks. Until then, this | |
1067 | * function may only be called from __kfree_rcu(). | |
1068 | * | |
1069 | * Because there is no preemptible RCU, we use RCU-sched instead. | |
1070 | */ | |
1071 | void kfree_call_rcu(struct rcu_head *head, | |
1072 | void (*func)(struct rcu_head *rcu)) | |
1073 | { | |
3fbfbf7a | 1074 | __call_rcu(head, func, &rcu_sched_state, -1, 1); |
486e2593 PM |
1075 | } |
1076 | EXPORT_SYMBOL_GPL(kfree_call_rcu); | |
1077 | ||
019129d5 PM |
1078 | /* |
1079 | * Wait for an rcu-preempt grace period, but make it happen quickly. | |
6cc68793 | 1080 | * But because preemptible RCU does not exist, map to rcu-sched. |
019129d5 PM |
1081 | */ |
1082 | void synchronize_rcu_expedited(void) | |
1083 | { | |
1084 | synchronize_sched_expedited(); | |
1085 | } | |
1086 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
1087 | ||
d9a3da06 PM |
1088 | #ifdef CONFIG_HOTPLUG_CPU |
1089 | ||
1090 | /* | |
6cc68793 | 1091 | * Because preemptible RCU does not exist, there is never any need to |
d9a3da06 PM |
1092 | * report on tasks preempted in RCU read-side critical sections during |
1093 | * expedited RCU grace periods. | |
1094 | */ | |
b40d293e TG |
1095 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, |
1096 | bool wake) | |
d9a3da06 | 1097 | { |
d9a3da06 PM |
1098 | } |
1099 | ||
1100 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
1101 | ||
e74f4c45 | 1102 | /* |
6cc68793 | 1103 | * Because preemptible RCU does not exist, rcu_barrier() is just |
e74f4c45 PM |
1104 | * another name for rcu_barrier_sched(). |
1105 | */ | |
1106 | void rcu_barrier(void) | |
1107 | { | |
1108 | rcu_barrier_sched(); | |
1109 | } | |
1110 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
1111 | ||
1eba8f84 | 1112 | /* |
6cc68793 | 1113 | * Because preemptible RCU does not exist, it need not be initialized. |
1eba8f84 PM |
1114 | */ |
1115 | static void __init __rcu_init_preempt(void) | |
1116 | { | |
1117 | } | |
1118 | ||
2439b696 PM |
1119 | /* |
1120 | * Because preemptible RCU does not exist, tasks cannot possibly exit | |
1121 | * while in preemptible RCU read-side critical sections. | |
1122 | */ | |
1123 | void exit_rcu(void) | |
1124 | { | |
1125 | } | |
1126 | ||
f41d911f | 1127 | #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ |
8bd93a2c | 1128 | |
27f4d280 PM |
1129 | #ifdef CONFIG_RCU_BOOST |
1130 | ||
1131 | #include "rtmutex_common.h" | |
1132 | ||
0ea1f2eb PM |
1133 | #ifdef CONFIG_RCU_TRACE |
1134 | ||
1135 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) | |
1136 | { | |
1137 | if (list_empty(&rnp->blkd_tasks)) | |
1138 | rnp->n_balk_blkd_tasks++; | |
1139 | else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL) | |
1140 | rnp->n_balk_exp_gp_tasks++; | |
1141 | else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL) | |
1142 | rnp->n_balk_boost_tasks++; | |
1143 | else if (rnp->gp_tasks != NULL && rnp->qsmask != 0) | |
1144 | rnp->n_balk_notblocked++; | |
1145 | else if (rnp->gp_tasks != NULL && | |
a9f4793d | 1146 | ULONG_CMP_LT(jiffies, rnp->boost_time)) |
0ea1f2eb PM |
1147 | rnp->n_balk_notyet++; |
1148 | else | |
1149 | rnp->n_balk_nos++; | |
1150 | } | |
1151 | ||
1152 | #else /* #ifdef CONFIG_RCU_TRACE */ | |
1153 | ||
1154 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) | |
1155 | { | |
1156 | } | |
1157 | ||
1158 | #endif /* #else #ifdef CONFIG_RCU_TRACE */ | |
1159 | ||
5d01bbd1 TG |
1160 | static void rcu_wake_cond(struct task_struct *t, int status) |
1161 | { | |
1162 | /* | |
1163 | * If the thread is yielding, only wake it when this | |
1164 | * is invoked from idle | |
1165 | */ | |
1166 | if (status != RCU_KTHREAD_YIELDING || is_idle_task(current)) | |
1167 | wake_up_process(t); | |
1168 | } | |
1169 | ||
27f4d280 PM |
1170 | /* |
1171 | * Carry out RCU priority boosting on the task indicated by ->exp_tasks | |
1172 | * or ->boost_tasks, advancing the pointer to the next task in the | |
1173 | * ->blkd_tasks list. | |
1174 | * | |
1175 | * Note that irqs must be enabled: boosting the task can block. | |
1176 | * Returns 1 if there are more tasks needing to be boosted. | |
1177 | */ | |
1178 | static int rcu_boost(struct rcu_node *rnp) | |
1179 | { | |
1180 | unsigned long flags; | |
1181 | struct rt_mutex mtx; | |
1182 | struct task_struct *t; | |
1183 | struct list_head *tb; | |
1184 | ||
1185 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) | |
1186 | return 0; /* Nothing left to boost. */ | |
1187 | ||
1188 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
1189 | ||
1190 | /* | |
1191 | * Recheck under the lock: all tasks in need of boosting | |
1192 | * might exit their RCU read-side critical sections on their own. | |
1193 | */ | |
1194 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { | |
1195 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
1196 | return 0; | |
1197 | } | |
1198 | ||
1199 | /* | |
1200 | * Preferentially boost tasks blocking expedited grace periods. | |
1201 | * This cannot starve the normal grace periods because a second | |
1202 | * expedited grace period must boost all blocked tasks, including | |
1203 | * those blocking the pre-existing normal grace period. | |
1204 | */ | |
0ea1f2eb | 1205 | if (rnp->exp_tasks != NULL) { |
27f4d280 | 1206 | tb = rnp->exp_tasks; |
0ea1f2eb PM |
1207 | rnp->n_exp_boosts++; |
1208 | } else { | |
27f4d280 | 1209 | tb = rnp->boost_tasks; |
0ea1f2eb PM |
1210 | rnp->n_normal_boosts++; |
1211 | } | |
1212 | rnp->n_tasks_boosted++; | |
27f4d280 PM |
1213 | |
1214 | /* | |
1215 | * We boost task t by manufacturing an rt_mutex that appears to | |
1216 | * be held by task t. We leave a pointer to that rt_mutex where | |
1217 | * task t can find it, and task t will release the mutex when it | |
1218 | * exits its outermost RCU read-side critical section. Then | |
1219 | * simply acquiring this artificial rt_mutex will boost task | |
1220 | * t's priority. (Thanks to tglx for suggesting this approach!) | |
1221 | * | |
1222 | * Note that task t must acquire rnp->lock to remove itself from | |
1223 | * the ->blkd_tasks list, which it will do from exit() if from | |
1224 | * nowhere else. We therefore are guaranteed that task t will | |
1225 | * stay around at least until we drop rnp->lock. Note that | |
1226 | * rnp->lock also resolves races between our priority boosting | |
1227 | * and task t's exiting its outermost RCU read-side critical | |
1228 | * section. | |
1229 | */ | |
1230 | t = container_of(tb, struct task_struct, rcu_node_entry); | |
1231 | rt_mutex_init_proxy_locked(&mtx, t); | |
1232 | t->rcu_boost_mutex = &mtx; | |
27f4d280 PM |
1233 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1234 | rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */ | |
1235 | rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ | |
1236 | ||
4f89b336 PM |
1237 | return ACCESS_ONCE(rnp->exp_tasks) != NULL || |
1238 | ACCESS_ONCE(rnp->boost_tasks) != NULL; | |
27f4d280 PM |
1239 | } |
1240 | ||
27f4d280 PM |
1241 | /* |
1242 | * Priority-boosting kthread. One per leaf rcu_node and one for the | |
1243 | * root rcu_node. | |
1244 | */ | |
1245 | static int rcu_boost_kthread(void *arg) | |
1246 | { | |
1247 | struct rcu_node *rnp = (struct rcu_node *)arg; | |
1248 | int spincnt = 0; | |
1249 | int more2boost; | |
1250 | ||
f7f7bac9 | 1251 | trace_rcu_utilization(TPS("Start boost kthread@init")); |
27f4d280 | 1252 | for (;;) { |
d71df90e | 1253 | rnp->boost_kthread_status = RCU_KTHREAD_WAITING; |
f7f7bac9 | 1254 | trace_rcu_utilization(TPS("End boost kthread@rcu_wait")); |
08bca60a | 1255 | rcu_wait(rnp->boost_tasks || rnp->exp_tasks); |
f7f7bac9 | 1256 | trace_rcu_utilization(TPS("Start boost kthread@rcu_wait")); |
d71df90e | 1257 | rnp->boost_kthread_status = RCU_KTHREAD_RUNNING; |
27f4d280 PM |
1258 | more2boost = rcu_boost(rnp); |
1259 | if (more2boost) | |
1260 | spincnt++; | |
1261 | else | |
1262 | spincnt = 0; | |
1263 | if (spincnt > 10) { | |
5d01bbd1 | 1264 | rnp->boost_kthread_status = RCU_KTHREAD_YIELDING; |
f7f7bac9 | 1265 | trace_rcu_utilization(TPS("End boost kthread@rcu_yield")); |
5d01bbd1 | 1266 | schedule_timeout_interruptible(2); |
f7f7bac9 | 1267 | trace_rcu_utilization(TPS("Start boost kthread@rcu_yield")); |
27f4d280 PM |
1268 | spincnt = 0; |
1269 | } | |
1270 | } | |
1217ed1b | 1271 | /* NOTREACHED */ |
f7f7bac9 | 1272 | trace_rcu_utilization(TPS("End boost kthread@notreached")); |
27f4d280 PM |
1273 | return 0; |
1274 | } | |
1275 | ||
1276 | /* | |
1277 | * Check to see if it is time to start boosting RCU readers that are | |
1278 | * blocking the current grace period, and, if so, tell the per-rcu_node | |
1279 | * kthread to start boosting them. If there is an expedited grace | |
1280 | * period in progress, it is always time to boost. | |
1281 | * | |
b065a853 PM |
1282 | * The caller must hold rnp->lock, which this function releases. |
1283 | * The ->boost_kthread_task is immortal, so we don't need to worry | |
1284 | * about it going away. | |
27f4d280 | 1285 | */ |
1217ed1b | 1286 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
27f4d280 PM |
1287 | { |
1288 | struct task_struct *t; | |
1289 | ||
0ea1f2eb PM |
1290 | if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { |
1291 | rnp->n_balk_exp_gp_tasks++; | |
1217ed1b | 1292 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 | 1293 | return; |
0ea1f2eb | 1294 | } |
27f4d280 PM |
1295 | if (rnp->exp_tasks != NULL || |
1296 | (rnp->gp_tasks != NULL && | |
1297 | rnp->boost_tasks == NULL && | |
1298 | rnp->qsmask == 0 && | |
1299 | ULONG_CMP_GE(jiffies, rnp->boost_time))) { | |
1300 | if (rnp->exp_tasks == NULL) | |
1301 | rnp->boost_tasks = rnp->gp_tasks; | |
1217ed1b | 1302 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 | 1303 | t = rnp->boost_kthread_task; |
5d01bbd1 TG |
1304 | if (t) |
1305 | rcu_wake_cond(t, rnp->boost_kthread_status); | |
1217ed1b | 1306 | } else { |
0ea1f2eb | 1307 | rcu_initiate_boost_trace(rnp); |
1217ed1b PM |
1308 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1309 | } | |
27f4d280 PM |
1310 | } |
1311 | ||
a46e0899 PM |
1312 | /* |
1313 | * Wake up the per-CPU kthread to invoke RCU callbacks. | |
1314 | */ | |
1315 | static void invoke_rcu_callbacks_kthread(void) | |
1316 | { | |
1317 | unsigned long flags; | |
1318 | ||
1319 | local_irq_save(flags); | |
1320 | __this_cpu_write(rcu_cpu_has_work, 1); | |
1eb52121 | 1321 | if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && |
5d01bbd1 TG |
1322 | current != __this_cpu_read(rcu_cpu_kthread_task)) { |
1323 | rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), | |
1324 | __this_cpu_read(rcu_cpu_kthread_status)); | |
1325 | } | |
a46e0899 PM |
1326 | local_irq_restore(flags); |
1327 | } | |
1328 | ||
dff1672d PM |
1329 | /* |
1330 | * Is the current CPU running the RCU-callbacks kthread? | |
1331 | * Caller must have preemption disabled. | |
1332 | */ | |
1333 | static bool rcu_is_callbacks_kthread(void) | |
1334 | { | |
1335 | return __get_cpu_var(rcu_cpu_kthread_task) == current; | |
1336 | } | |
1337 | ||
27f4d280 PM |
1338 | #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) |
1339 | ||
1340 | /* | |
1341 | * Do priority-boost accounting for the start of a new grace period. | |
1342 | */ | |
1343 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) | |
1344 | { | |
1345 | rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; | |
1346 | } | |
1347 | ||
27f4d280 PM |
1348 | /* |
1349 | * Create an RCU-boost kthread for the specified node if one does not | |
1350 | * already exist. We only create this kthread for preemptible RCU. | |
1351 | * Returns zero if all is well, a negated errno otherwise. | |
1352 | */ | |
49fb4c62 | 1353 | static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp, |
5d01bbd1 | 1354 | struct rcu_node *rnp) |
27f4d280 | 1355 | { |
5d01bbd1 | 1356 | int rnp_index = rnp - &rsp->node[0]; |
27f4d280 PM |
1357 | unsigned long flags; |
1358 | struct sched_param sp; | |
1359 | struct task_struct *t; | |
1360 | ||
1361 | if (&rcu_preempt_state != rsp) | |
1362 | return 0; | |
5d01bbd1 TG |
1363 | |
1364 | if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0) | |
1365 | return 0; | |
1366 | ||
a46e0899 | 1367 | rsp->boost = 1; |
27f4d280 PM |
1368 | if (rnp->boost_kthread_task != NULL) |
1369 | return 0; | |
1370 | t = kthread_create(rcu_boost_kthread, (void *)rnp, | |
5b61b0ba | 1371 | "rcub/%d", rnp_index); |
27f4d280 PM |
1372 | if (IS_ERR(t)) |
1373 | return PTR_ERR(t); | |
1374 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
1375 | rnp->boost_kthread_task = t; | |
1376 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
5b61b0ba | 1377 | sp.sched_priority = RCU_BOOST_PRIO; |
27f4d280 | 1378 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); |
9a432736 | 1379 | wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ |
27f4d280 PM |
1380 | return 0; |
1381 | } | |
1382 | ||
f8b7fc6b PM |
1383 | static void rcu_kthread_do_work(void) |
1384 | { | |
1385 | rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data)); | |
1386 | rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data)); | |
1387 | rcu_preempt_do_callbacks(); | |
1388 | } | |
1389 | ||
62ab7072 | 1390 | static void rcu_cpu_kthread_setup(unsigned int cpu) |
f8b7fc6b | 1391 | { |
f8b7fc6b | 1392 | struct sched_param sp; |
f8b7fc6b | 1393 | |
62ab7072 PM |
1394 | sp.sched_priority = RCU_KTHREAD_PRIO; |
1395 | sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); | |
f8b7fc6b PM |
1396 | } |
1397 | ||
62ab7072 | 1398 | static void rcu_cpu_kthread_park(unsigned int cpu) |
f8b7fc6b | 1399 | { |
62ab7072 | 1400 | per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; |
f8b7fc6b PM |
1401 | } |
1402 | ||
62ab7072 | 1403 | static int rcu_cpu_kthread_should_run(unsigned int cpu) |
f8b7fc6b | 1404 | { |
62ab7072 | 1405 | return __get_cpu_var(rcu_cpu_has_work); |
f8b7fc6b PM |
1406 | } |
1407 | ||
1408 | /* | |
1409 | * Per-CPU kernel thread that invokes RCU callbacks. This replaces the | |
e0f23060 PM |
1410 | * RCU softirq used in flavors and configurations of RCU that do not |
1411 | * support RCU priority boosting. | |
f8b7fc6b | 1412 | */ |
62ab7072 | 1413 | static void rcu_cpu_kthread(unsigned int cpu) |
f8b7fc6b | 1414 | { |
62ab7072 PM |
1415 | unsigned int *statusp = &__get_cpu_var(rcu_cpu_kthread_status); |
1416 | char work, *workp = &__get_cpu_var(rcu_cpu_has_work); | |
1417 | int spincnt; | |
f8b7fc6b | 1418 | |
62ab7072 | 1419 | for (spincnt = 0; spincnt < 10; spincnt++) { |
f7f7bac9 | 1420 | trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait")); |
f8b7fc6b | 1421 | local_bh_disable(); |
f8b7fc6b | 1422 | *statusp = RCU_KTHREAD_RUNNING; |
62ab7072 PM |
1423 | this_cpu_inc(rcu_cpu_kthread_loops); |
1424 | local_irq_disable(); | |
f8b7fc6b PM |
1425 | work = *workp; |
1426 | *workp = 0; | |
62ab7072 | 1427 | local_irq_enable(); |
f8b7fc6b PM |
1428 | if (work) |
1429 | rcu_kthread_do_work(); | |
1430 | local_bh_enable(); | |
62ab7072 | 1431 | if (*workp == 0) { |
f7f7bac9 | 1432 | trace_rcu_utilization(TPS("End CPU kthread@rcu_wait")); |
62ab7072 PM |
1433 | *statusp = RCU_KTHREAD_WAITING; |
1434 | return; | |
f8b7fc6b PM |
1435 | } |
1436 | } | |
62ab7072 | 1437 | *statusp = RCU_KTHREAD_YIELDING; |
f7f7bac9 | 1438 | trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield")); |
62ab7072 | 1439 | schedule_timeout_interruptible(2); |
f7f7bac9 | 1440 | trace_rcu_utilization(TPS("End CPU kthread@rcu_yield")); |
62ab7072 | 1441 | *statusp = RCU_KTHREAD_WAITING; |
f8b7fc6b PM |
1442 | } |
1443 | ||
1444 | /* | |
1445 | * Set the per-rcu_node kthread's affinity to cover all CPUs that are | |
1446 | * served by the rcu_node in question. The CPU hotplug lock is still | |
1447 | * held, so the value of rnp->qsmaskinit will be stable. | |
1448 | * | |
1449 | * We don't include outgoingcpu in the affinity set, use -1 if there is | |
1450 | * no outgoing CPU. If there are no CPUs left in the affinity set, | |
1451 | * this function allows the kthread to execute on any CPU. | |
1452 | */ | |
5d01bbd1 | 1453 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
f8b7fc6b | 1454 | { |
5d01bbd1 TG |
1455 | struct task_struct *t = rnp->boost_kthread_task; |
1456 | unsigned long mask = rnp->qsmaskinit; | |
f8b7fc6b PM |
1457 | cpumask_var_t cm; |
1458 | int cpu; | |
f8b7fc6b | 1459 | |
5d01bbd1 | 1460 | if (!t) |
f8b7fc6b | 1461 | return; |
5d01bbd1 | 1462 | if (!zalloc_cpumask_var(&cm, GFP_KERNEL)) |
f8b7fc6b | 1463 | return; |
f8b7fc6b PM |
1464 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) |
1465 | if ((mask & 0x1) && cpu != outgoingcpu) | |
1466 | cpumask_set_cpu(cpu, cm); | |
1467 | if (cpumask_weight(cm) == 0) { | |
1468 | cpumask_setall(cm); | |
1469 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) | |
1470 | cpumask_clear_cpu(cpu, cm); | |
1471 | WARN_ON_ONCE(cpumask_weight(cm) == 0); | |
1472 | } | |
5d01bbd1 | 1473 | set_cpus_allowed_ptr(t, cm); |
f8b7fc6b PM |
1474 | free_cpumask_var(cm); |
1475 | } | |
1476 | ||
62ab7072 PM |
1477 | static struct smp_hotplug_thread rcu_cpu_thread_spec = { |
1478 | .store = &rcu_cpu_kthread_task, | |
1479 | .thread_should_run = rcu_cpu_kthread_should_run, | |
1480 | .thread_fn = rcu_cpu_kthread, | |
1481 | .thread_comm = "rcuc/%u", | |
1482 | .setup = rcu_cpu_kthread_setup, | |
1483 | .park = rcu_cpu_kthread_park, | |
1484 | }; | |
f8b7fc6b PM |
1485 | |
1486 | /* | |
1487 | * Spawn all kthreads -- called as soon as the scheduler is running. | |
1488 | */ | |
1489 | static int __init rcu_spawn_kthreads(void) | |
1490 | { | |
f8b7fc6b | 1491 | struct rcu_node *rnp; |
5d01bbd1 | 1492 | int cpu; |
f8b7fc6b | 1493 | |
b0d30417 | 1494 | rcu_scheduler_fully_active = 1; |
62ab7072 | 1495 | for_each_possible_cpu(cpu) |
f8b7fc6b | 1496 | per_cpu(rcu_cpu_has_work, cpu) = 0; |
62ab7072 | 1497 | BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec)); |
f8b7fc6b | 1498 | rnp = rcu_get_root(rcu_state); |
5d01bbd1 | 1499 | (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); |
f8b7fc6b PM |
1500 | if (NUM_RCU_NODES > 1) { |
1501 | rcu_for_each_leaf_node(rcu_state, rnp) | |
5d01bbd1 | 1502 | (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); |
f8b7fc6b PM |
1503 | } |
1504 | return 0; | |
1505 | } | |
1506 | early_initcall(rcu_spawn_kthreads); | |
1507 | ||
49fb4c62 | 1508 | static void rcu_prepare_kthreads(int cpu) |
f8b7fc6b PM |
1509 | { |
1510 | struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu); | |
1511 | struct rcu_node *rnp = rdp->mynode; | |
1512 | ||
1513 | /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ | |
62ab7072 | 1514 | if (rcu_scheduler_fully_active) |
5d01bbd1 | 1515 | (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); |
f8b7fc6b PM |
1516 | } |
1517 | ||
27f4d280 PM |
1518 | #else /* #ifdef CONFIG_RCU_BOOST */ |
1519 | ||
1217ed1b | 1520 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
27f4d280 | 1521 | { |
1217ed1b | 1522 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 PM |
1523 | } |
1524 | ||
a46e0899 | 1525 | static void invoke_rcu_callbacks_kthread(void) |
27f4d280 | 1526 | { |
a46e0899 | 1527 | WARN_ON_ONCE(1); |
27f4d280 PM |
1528 | } |
1529 | ||
dff1672d PM |
1530 | static bool rcu_is_callbacks_kthread(void) |
1531 | { | |
1532 | return false; | |
1533 | } | |
1534 | ||
27f4d280 PM |
1535 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) |
1536 | { | |
1537 | } | |
1538 | ||
5d01bbd1 | 1539 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
f8b7fc6b PM |
1540 | { |
1541 | } | |
1542 | ||
b0d30417 PM |
1543 | static int __init rcu_scheduler_really_started(void) |
1544 | { | |
1545 | rcu_scheduler_fully_active = 1; | |
1546 | return 0; | |
1547 | } | |
1548 | early_initcall(rcu_scheduler_really_started); | |
1549 | ||
49fb4c62 | 1550 | static void rcu_prepare_kthreads(int cpu) |
f8b7fc6b PM |
1551 | { |
1552 | } | |
1553 | ||
27f4d280 PM |
1554 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
1555 | ||
8bd93a2c PM |
1556 | #if !defined(CONFIG_RCU_FAST_NO_HZ) |
1557 | ||
1558 | /* | |
1559 | * Check to see if any future RCU-related work will need to be done | |
1560 | * by the current CPU, even if none need be done immediately, returning | |
1561 | * 1 if so. This function is part of the RCU implementation; it is -not- | |
1562 | * an exported member of the RCU API. | |
1563 | * | |
7cb92499 PM |
1564 | * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs |
1565 | * any flavor of RCU. | |
8bd93a2c | 1566 | */ |
aa9b1630 | 1567 | int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) |
8bd93a2c | 1568 | { |
aa9b1630 | 1569 | *delta_jiffies = ULONG_MAX; |
c0f4dfd4 | 1570 | return rcu_cpu_has_callbacks(cpu, NULL); |
7cb92499 PM |
1571 | } |
1572 | ||
1573 | /* | |
1574 | * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up | |
1575 | * after it. | |
1576 | */ | |
1577 | static void rcu_cleanup_after_idle(int cpu) | |
1578 | { | |
1579 | } | |
1580 | ||
aea1b35e | 1581 | /* |
a858af28 | 1582 | * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n, |
aea1b35e PM |
1583 | * is nothing. |
1584 | */ | |
1585 | static void rcu_prepare_for_idle(int cpu) | |
1586 | { | |
1587 | } | |
1588 | ||
c57afe80 PM |
1589 | /* |
1590 | * Don't bother keeping a running count of the number of RCU callbacks | |
1591 | * posted because CONFIG_RCU_FAST_NO_HZ=n. | |
1592 | */ | |
1593 | static void rcu_idle_count_callbacks_posted(void) | |
1594 | { | |
1595 | } | |
1596 | ||
8bd93a2c PM |
1597 | #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
1598 | ||
f23f7fa1 PM |
1599 | /* |
1600 | * This code is invoked when a CPU goes idle, at which point we want | |
1601 | * to have the CPU do everything required for RCU so that it can enter | |
1602 | * the energy-efficient dyntick-idle mode. This is handled by a | |
1603 | * state machine implemented by rcu_prepare_for_idle() below. | |
1604 | * | |
1605 | * The following three proprocessor symbols control this state machine: | |
1606 | * | |
f23f7fa1 PM |
1607 | * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted |
1608 | * to sleep in dyntick-idle mode with RCU callbacks pending. This | |
1609 | * is sized to be roughly one RCU grace period. Those energy-efficiency | |
1610 | * benchmarkers who might otherwise be tempted to set this to a large | |
1611 | * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your | |
1612 | * system. And if you are -that- concerned about energy efficiency, | |
1613 | * just power the system down and be done with it! | |
778d250a PM |
1614 | * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is |
1615 | * permitted to sleep in dyntick-idle mode with only lazy RCU | |
1616 | * callbacks pending. Setting this too high can OOM your system. | |
f23f7fa1 PM |
1617 | * |
1618 | * The values below work well in practice. If future workloads require | |
1619 | * adjustment, they can be converted into kernel config parameters, though | |
1620 | * making the state machine smarter might be a better option. | |
1621 | */ | |
e84c48ae | 1622 | #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */ |
778d250a | 1623 | #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ |
f23f7fa1 | 1624 | |
5e44ce35 PM |
1625 | static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY; |
1626 | module_param(rcu_idle_gp_delay, int, 0644); | |
1627 | static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY; | |
1628 | module_param(rcu_idle_lazy_gp_delay, int, 0644); | |
486e2593 | 1629 | |
9d2ad243 | 1630 | extern int tick_nohz_enabled; |
486e2593 PM |
1631 | |
1632 | /* | |
c0f4dfd4 PM |
1633 | * Try to advance callbacks for all flavors of RCU on the current CPU. |
1634 | * Afterwards, if there are any callbacks ready for immediate invocation, | |
1635 | * return true. | |
486e2593 | 1636 | */ |
c0f4dfd4 | 1637 | static bool rcu_try_advance_all_cbs(void) |
486e2593 | 1638 | { |
c0f4dfd4 PM |
1639 | bool cbs_ready = false; |
1640 | struct rcu_data *rdp; | |
1641 | struct rcu_node *rnp; | |
1642 | struct rcu_state *rsp; | |
486e2593 | 1643 | |
c0f4dfd4 PM |
1644 | for_each_rcu_flavor(rsp) { |
1645 | rdp = this_cpu_ptr(rsp->rda); | |
1646 | rnp = rdp->mynode; | |
486e2593 | 1647 | |
c0f4dfd4 PM |
1648 | /* |
1649 | * Don't bother checking unless a grace period has | |
1650 | * completed since we last checked and there are | |
1651 | * callbacks not yet ready to invoke. | |
1652 | */ | |
1653 | if (rdp->completed != rnp->completed && | |
1654 | rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL]) | |
470716fc | 1655 | note_gp_changes(rsp, rdp); |
486e2593 | 1656 | |
c0f4dfd4 PM |
1657 | if (cpu_has_callbacks_ready_to_invoke(rdp)) |
1658 | cbs_ready = true; | |
1659 | } | |
1660 | return cbs_ready; | |
486e2593 PM |
1661 | } |
1662 | ||
aa9b1630 | 1663 | /* |
c0f4dfd4 PM |
1664 | * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready |
1665 | * to invoke. If the CPU has callbacks, try to advance them. Tell the | |
1666 | * caller to set the timeout based on whether or not there are non-lazy | |
1667 | * callbacks. | |
aa9b1630 | 1668 | * |
c0f4dfd4 | 1669 | * The caller must have disabled interrupts. |
aa9b1630 | 1670 | */ |
c0f4dfd4 | 1671 | int rcu_needs_cpu(int cpu, unsigned long *dj) |
aa9b1630 PM |
1672 | { |
1673 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); | |
1674 | ||
c0f4dfd4 PM |
1675 | /* Snapshot to detect later posting of non-lazy callback. */ |
1676 | rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; | |
1677 | ||
aa9b1630 | 1678 | /* If no callbacks, RCU doesn't need the CPU. */ |
c0f4dfd4 PM |
1679 | if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) { |
1680 | *dj = ULONG_MAX; | |
aa9b1630 PM |
1681 | return 0; |
1682 | } | |
c0f4dfd4 PM |
1683 | |
1684 | /* Attempt to advance callbacks. */ | |
1685 | if (rcu_try_advance_all_cbs()) { | |
1686 | /* Some ready to invoke, so initiate later invocation. */ | |
1687 | invoke_rcu_core(); | |
aa9b1630 PM |
1688 | return 1; |
1689 | } | |
c0f4dfd4 PM |
1690 | rdtp->last_accelerate = jiffies; |
1691 | ||
1692 | /* Request timer delay depending on laziness, and round. */ | |
6faf7283 | 1693 | if (!rdtp->all_lazy) { |
c0f4dfd4 PM |
1694 | *dj = round_up(rcu_idle_gp_delay + jiffies, |
1695 | rcu_idle_gp_delay) - jiffies; | |
e84c48ae | 1696 | } else { |
c0f4dfd4 | 1697 | *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies; |
e84c48ae | 1698 | } |
aa9b1630 PM |
1699 | return 0; |
1700 | } | |
1701 | ||
21e52e15 | 1702 | /* |
c0f4dfd4 PM |
1703 | * Prepare a CPU for idle from an RCU perspective. The first major task |
1704 | * is to sense whether nohz mode has been enabled or disabled via sysfs. | |
1705 | * The second major task is to check to see if a non-lazy callback has | |
1706 | * arrived at a CPU that previously had only lazy callbacks. The third | |
1707 | * major task is to accelerate (that is, assign grace-period numbers to) | |
1708 | * any recently arrived callbacks. | |
aea1b35e PM |
1709 | * |
1710 | * The caller must have disabled interrupts. | |
8bd93a2c | 1711 | */ |
aea1b35e | 1712 | static void rcu_prepare_for_idle(int cpu) |
8bd93a2c | 1713 | { |
c0f4dfd4 | 1714 | struct rcu_data *rdp; |
5955f7ee | 1715 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
c0f4dfd4 PM |
1716 | struct rcu_node *rnp; |
1717 | struct rcu_state *rsp; | |
9d2ad243 PM |
1718 | int tne; |
1719 | ||
1720 | /* Handle nohz enablement switches conservatively. */ | |
1721 | tne = ACCESS_ONCE(tick_nohz_enabled); | |
1722 | if (tne != rdtp->tick_nohz_enabled_snap) { | |
c0f4dfd4 | 1723 | if (rcu_cpu_has_callbacks(cpu, NULL)) |
9d2ad243 PM |
1724 | invoke_rcu_core(); /* force nohz to see update. */ |
1725 | rdtp->tick_nohz_enabled_snap = tne; | |
1726 | return; | |
1727 | } | |
1728 | if (!tne) | |
1729 | return; | |
f511fc62 | 1730 | |
c0f4dfd4 | 1731 | /* If this is a no-CBs CPU, no callbacks, just return. */ |
534c97b0 | 1732 | if (rcu_is_nocb_cpu(cpu)) |
9a0c6fef | 1733 | return; |
9a0c6fef | 1734 | |
c57afe80 | 1735 | /* |
c0f4dfd4 PM |
1736 | * If a non-lazy callback arrived at a CPU having only lazy |
1737 | * callbacks, invoke RCU core for the side-effect of recalculating | |
1738 | * idle duration on re-entry to idle. | |
c57afe80 | 1739 | */ |
c0f4dfd4 PM |
1740 | if (rdtp->all_lazy && |
1741 | rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) { | |
1742 | invoke_rcu_core(); | |
c57afe80 PM |
1743 | return; |
1744 | } | |
c57afe80 | 1745 | |
3084f2f8 | 1746 | /* |
c0f4dfd4 PM |
1747 | * If we have not yet accelerated this jiffy, accelerate all |
1748 | * callbacks on this CPU. | |
3084f2f8 | 1749 | */ |
c0f4dfd4 | 1750 | if (rdtp->last_accelerate == jiffies) |
aea1b35e | 1751 | return; |
c0f4dfd4 PM |
1752 | rdtp->last_accelerate = jiffies; |
1753 | for_each_rcu_flavor(rsp) { | |
1754 | rdp = per_cpu_ptr(rsp->rda, cpu); | |
1755 | if (!*rdp->nxttail[RCU_DONE_TAIL]) | |
1756 | continue; | |
1757 | rnp = rdp->mynode; | |
1758 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ | |
1759 | rcu_accelerate_cbs(rsp, rnp, rdp); | |
1760 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ | |
77e38ed3 | 1761 | } |
c0f4dfd4 | 1762 | } |
3084f2f8 | 1763 | |
c0f4dfd4 PM |
1764 | /* |
1765 | * Clean up for exit from idle. Attempt to advance callbacks based on | |
1766 | * any grace periods that elapsed while the CPU was idle, and if any | |
1767 | * callbacks are now ready to invoke, initiate invocation. | |
1768 | */ | |
1769 | static void rcu_cleanup_after_idle(int cpu) | |
1770 | { | |
1771 | struct rcu_data *rdp; | |
1772 | struct rcu_state *rsp; | |
a47cd880 | 1773 | |
534c97b0 | 1774 | if (rcu_is_nocb_cpu(cpu)) |
aea1b35e | 1775 | return; |
c0f4dfd4 PM |
1776 | rcu_try_advance_all_cbs(); |
1777 | for_each_rcu_flavor(rsp) { | |
1778 | rdp = per_cpu_ptr(rsp->rda, cpu); | |
1779 | if (cpu_has_callbacks_ready_to_invoke(rdp)) | |
1780 | invoke_rcu_core(); | |
c701d5d9 | 1781 | } |
8bd93a2c PM |
1782 | } |
1783 | ||
c57afe80 | 1784 | /* |
98248a0e PM |
1785 | * Keep a running count of the number of non-lazy callbacks posted |
1786 | * on this CPU. This running counter (which is never decremented) allows | |
1787 | * rcu_prepare_for_idle() to detect when something out of the idle loop | |
1788 | * posts a callback, even if an equal number of callbacks are invoked. | |
1789 | * Of course, callbacks should only be posted from within a trace event | |
1790 | * designed to be called from idle or from within RCU_NONIDLE(). | |
c57afe80 PM |
1791 | */ |
1792 | static void rcu_idle_count_callbacks_posted(void) | |
1793 | { | |
5955f7ee | 1794 | __this_cpu_add(rcu_dynticks.nonlazy_posted, 1); |
c57afe80 PM |
1795 | } |
1796 | ||
b626c1b6 PM |
1797 | /* |
1798 | * Data for flushing lazy RCU callbacks at OOM time. | |
1799 | */ | |
1800 | static atomic_t oom_callback_count; | |
1801 | static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq); | |
1802 | ||
1803 | /* | |
1804 | * RCU OOM callback -- decrement the outstanding count and deliver the | |
1805 | * wake-up if we are the last one. | |
1806 | */ | |
1807 | static void rcu_oom_callback(struct rcu_head *rhp) | |
1808 | { | |
1809 | if (atomic_dec_and_test(&oom_callback_count)) | |
1810 | wake_up(&oom_callback_wq); | |
1811 | } | |
1812 | ||
1813 | /* | |
1814 | * Post an rcu_oom_notify callback on the current CPU if it has at | |
1815 | * least one lazy callback. This will unnecessarily post callbacks | |
1816 | * to CPUs that already have a non-lazy callback at the end of their | |
1817 | * callback list, but this is an infrequent operation, so accept some | |
1818 | * extra overhead to keep things simple. | |
1819 | */ | |
1820 | static void rcu_oom_notify_cpu(void *unused) | |
1821 | { | |
1822 | struct rcu_state *rsp; | |
1823 | struct rcu_data *rdp; | |
1824 | ||
1825 | for_each_rcu_flavor(rsp) { | |
1826 | rdp = __this_cpu_ptr(rsp->rda); | |
1827 | if (rdp->qlen_lazy != 0) { | |
1828 | atomic_inc(&oom_callback_count); | |
1829 | rsp->call(&rdp->oom_head, rcu_oom_callback); | |
1830 | } | |
1831 | } | |
1832 | } | |
1833 | ||
1834 | /* | |
1835 | * If low on memory, ensure that each CPU has a non-lazy callback. | |
1836 | * This will wake up CPUs that have only lazy callbacks, in turn | |
1837 | * ensuring that they free up the corresponding memory in a timely manner. | |
1838 | * Because an uncertain amount of memory will be freed in some uncertain | |
1839 | * timeframe, we do not claim to have freed anything. | |
1840 | */ | |
1841 | static int rcu_oom_notify(struct notifier_block *self, | |
1842 | unsigned long notused, void *nfreed) | |
1843 | { | |
1844 | int cpu; | |
1845 | ||
1846 | /* Wait for callbacks from earlier instance to complete. */ | |
1847 | wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0); | |
1848 | ||
1849 | /* | |
1850 | * Prevent premature wakeup: ensure that all increments happen | |
1851 | * before there is a chance of the counter reaching zero. | |
1852 | */ | |
1853 | atomic_set(&oom_callback_count, 1); | |
1854 | ||
1855 | get_online_cpus(); | |
1856 | for_each_online_cpu(cpu) { | |
1857 | smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1); | |
1858 | cond_resched(); | |
1859 | } | |
1860 | put_online_cpus(); | |
1861 | ||
1862 | /* Unconditionally decrement: no need to wake ourselves up. */ | |
1863 | atomic_dec(&oom_callback_count); | |
1864 | ||
1865 | return NOTIFY_OK; | |
1866 | } | |
1867 | ||
1868 | static struct notifier_block rcu_oom_nb = { | |
1869 | .notifier_call = rcu_oom_notify | |
1870 | }; | |
1871 | ||
1872 | static int __init rcu_register_oom_notifier(void) | |
1873 | { | |
1874 | register_oom_notifier(&rcu_oom_nb); | |
1875 | return 0; | |
1876 | } | |
1877 | early_initcall(rcu_register_oom_notifier); | |
1878 | ||
8bd93a2c | 1879 | #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
a858af28 PM |
1880 | |
1881 | #ifdef CONFIG_RCU_CPU_STALL_INFO | |
1882 | ||
1883 | #ifdef CONFIG_RCU_FAST_NO_HZ | |
1884 | ||
1885 | static void print_cpu_stall_fast_no_hz(char *cp, int cpu) | |
1886 | { | |
5955f7ee | 1887 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
c0f4dfd4 | 1888 | unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap; |
a858af28 | 1889 | |
c0f4dfd4 PM |
1890 | sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c", |
1891 | rdtp->last_accelerate & 0xffff, jiffies & 0xffff, | |
1892 | ulong2long(nlpd), | |
1893 | rdtp->all_lazy ? 'L' : '.', | |
1894 | rdtp->tick_nohz_enabled_snap ? '.' : 'D'); | |
a858af28 PM |
1895 | } |
1896 | ||
1897 | #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ | |
1898 | ||
1899 | static void print_cpu_stall_fast_no_hz(char *cp, int cpu) | |
1900 | { | |
1c17e4d4 | 1901 | *cp = '\0'; |
a858af28 PM |
1902 | } |
1903 | ||
1904 | #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ | |
1905 | ||
1906 | /* Initiate the stall-info list. */ | |
1907 | static void print_cpu_stall_info_begin(void) | |
1908 | { | |
efc151c3 | 1909 | pr_cont("\n"); |
a858af28 PM |
1910 | } |
1911 | ||
1912 | /* | |
1913 | * Print out diagnostic information for the specified stalled CPU. | |
1914 | * | |
1915 | * If the specified CPU is aware of the current RCU grace period | |
1916 | * (flavor specified by rsp), then print the number of scheduling | |
1917 | * clock interrupts the CPU has taken during the time that it has | |
1918 | * been aware. Otherwise, print the number of RCU grace periods | |
1919 | * that this CPU is ignorant of, for example, "1" if the CPU was | |
1920 | * aware of the previous grace period. | |
1921 | * | |
1922 | * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. | |
1923 | */ | |
1924 | static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) | |
1925 | { | |
1926 | char fast_no_hz[72]; | |
1927 | struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); | |
1928 | struct rcu_dynticks *rdtp = rdp->dynticks; | |
1929 | char *ticks_title; | |
1930 | unsigned long ticks_value; | |
1931 | ||
1932 | if (rsp->gpnum == rdp->gpnum) { | |
1933 | ticks_title = "ticks this GP"; | |
1934 | ticks_value = rdp->ticks_this_gp; | |
1935 | } else { | |
1936 | ticks_title = "GPs behind"; | |
1937 | ticks_value = rsp->gpnum - rdp->gpnum; | |
1938 | } | |
1939 | print_cpu_stall_fast_no_hz(fast_no_hz, cpu); | |
efc151c3 | 1940 | pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n", |
a858af28 PM |
1941 | cpu, ticks_value, ticks_title, |
1942 | atomic_read(&rdtp->dynticks) & 0xfff, | |
1943 | rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting, | |
6231069b | 1944 | rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), |
a858af28 PM |
1945 | fast_no_hz); |
1946 | } | |
1947 | ||
1948 | /* Terminate the stall-info list. */ | |
1949 | static void print_cpu_stall_info_end(void) | |
1950 | { | |
efc151c3 | 1951 | pr_err("\t"); |
a858af28 PM |
1952 | } |
1953 | ||
1954 | /* Zero ->ticks_this_gp for all flavors of RCU. */ | |
1955 | static void zero_cpu_stall_ticks(struct rcu_data *rdp) | |
1956 | { | |
1957 | rdp->ticks_this_gp = 0; | |
6231069b | 1958 | rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id()); |
a858af28 PM |
1959 | } |
1960 | ||
1961 | /* Increment ->ticks_this_gp for all flavors of RCU. */ | |
1962 | static void increment_cpu_stall_ticks(void) | |
1963 | { | |
115f7a7c PM |
1964 | struct rcu_state *rsp; |
1965 | ||
1966 | for_each_rcu_flavor(rsp) | |
1967 | __this_cpu_ptr(rsp->rda)->ticks_this_gp++; | |
a858af28 PM |
1968 | } |
1969 | ||
1970 | #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ | |
1971 | ||
1972 | static void print_cpu_stall_info_begin(void) | |
1973 | { | |
efc151c3 | 1974 | pr_cont(" {"); |
a858af28 PM |
1975 | } |
1976 | ||
1977 | static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) | |
1978 | { | |
efc151c3 | 1979 | pr_cont(" %d", cpu); |
a858af28 PM |
1980 | } |
1981 | ||
1982 | static void print_cpu_stall_info_end(void) | |
1983 | { | |
efc151c3 | 1984 | pr_cont("} "); |
a858af28 PM |
1985 | } |
1986 | ||
1987 | static void zero_cpu_stall_ticks(struct rcu_data *rdp) | |
1988 | { | |
1989 | } | |
1990 | ||
1991 | static void increment_cpu_stall_ticks(void) | |
1992 | { | |
1993 | } | |
1994 | ||
1995 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ | |
3fbfbf7a PM |
1996 | |
1997 | #ifdef CONFIG_RCU_NOCB_CPU | |
1998 | ||
1999 | /* | |
2000 | * Offload callback processing from the boot-time-specified set of CPUs | |
2001 | * specified by rcu_nocb_mask. For each CPU in the set, there is a | |
2002 | * kthread created that pulls the callbacks from the corresponding CPU, | |
2003 | * waits for a grace period to elapse, and invokes the callbacks. | |
2004 | * The no-CBs CPUs do a wake_up() on their kthread when they insert | |
2005 | * a callback into any empty list, unless the rcu_nocb_poll boot parameter | |
2006 | * has been specified, in which case each kthread actively polls its | |
2007 | * CPU. (Which isn't so great for energy efficiency, but which does | |
2008 | * reduce RCU's overhead on that CPU.) | |
2009 | * | |
2010 | * This is intended to be used in conjunction with Frederic Weisbecker's | |
2011 | * adaptive-idle work, which would seriously reduce OS jitter on CPUs | |
2012 | * running CPU-bound user-mode computations. | |
2013 | * | |
2014 | * Offloading of callback processing could also in theory be used as | |
2015 | * an energy-efficiency measure because CPUs with no RCU callbacks | |
2016 | * queued are more aggressive about entering dyntick-idle mode. | |
2017 | */ | |
2018 | ||
2019 | ||
2020 | /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */ | |
2021 | static int __init rcu_nocb_setup(char *str) | |
2022 | { | |
2023 | alloc_bootmem_cpumask_var(&rcu_nocb_mask); | |
2024 | have_rcu_nocb_mask = true; | |
2025 | cpulist_parse(str, rcu_nocb_mask); | |
2026 | return 1; | |
2027 | } | |
2028 | __setup("rcu_nocbs=", rcu_nocb_setup); | |
2029 | ||
1b0048a4 PG |
2030 | static int __init parse_rcu_nocb_poll(char *arg) |
2031 | { | |
2032 | rcu_nocb_poll = 1; | |
2033 | return 0; | |
2034 | } | |
2035 | early_param("rcu_nocb_poll", parse_rcu_nocb_poll); | |
2036 | ||
34ed6246 | 2037 | /* |
dae6e64d PM |
2038 | * Do any no-CBs CPUs need another grace period? |
2039 | * | |
2040 | * Interrupts must be disabled. If the caller does not hold the root | |
2041 | * rnp_node structure's ->lock, the results are advisory only. | |
2042 | */ | |
2043 | static int rcu_nocb_needs_gp(struct rcu_state *rsp) | |
2044 | { | |
2045 | struct rcu_node *rnp = rcu_get_root(rsp); | |
2046 | ||
8b425aa8 | 2047 | return rnp->need_future_gp[(ACCESS_ONCE(rnp->completed) + 1) & 0x1]; |
dae6e64d PM |
2048 | } |
2049 | ||
2050 | /* | |
0446be48 PM |
2051 | * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended |
2052 | * grace period. | |
dae6e64d | 2053 | */ |
0446be48 | 2054 | static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) |
dae6e64d | 2055 | { |
0446be48 | 2056 | wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]); |
dae6e64d PM |
2057 | } |
2058 | ||
2059 | /* | |
8b425aa8 | 2060 | * Set the root rcu_node structure's ->need_future_gp field |
dae6e64d PM |
2061 | * based on the sum of those of all rcu_node structures. This does |
2062 | * double-count the root rcu_node structure's requests, but this | |
2063 | * is necessary to handle the possibility of a rcu_nocb_kthread() | |
2064 | * having awakened during the time that the rcu_node structures | |
2065 | * were being updated for the end of the previous grace period. | |
34ed6246 | 2066 | */ |
dae6e64d PM |
2067 | static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) |
2068 | { | |
8b425aa8 | 2069 | rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq; |
dae6e64d PM |
2070 | } |
2071 | ||
2072 | static void rcu_init_one_nocb(struct rcu_node *rnp) | |
34ed6246 | 2073 | { |
dae6e64d PM |
2074 | init_waitqueue_head(&rnp->nocb_gp_wq[0]); |
2075 | init_waitqueue_head(&rnp->nocb_gp_wq[1]); | |
34ed6246 PM |
2076 | } |
2077 | ||
3fbfbf7a | 2078 | /* Is the specified CPU a no-CPUs CPU? */ |
d1e43fa5 | 2079 | bool rcu_is_nocb_cpu(int cpu) |
3fbfbf7a PM |
2080 | { |
2081 | if (have_rcu_nocb_mask) | |
2082 | return cpumask_test_cpu(cpu, rcu_nocb_mask); | |
2083 | return false; | |
2084 | } | |
2085 | ||
2086 | /* | |
2087 | * Enqueue the specified string of rcu_head structures onto the specified | |
2088 | * CPU's no-CBs lists. The CPU is specified by rdp, the head of the | |
2089 | * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy | |
2090 | * counts are supplied by rhcount and rhcount_lazy. | |
2091 | * | |
2092 | * If warranted, also wake up the kthread servicing this CPUs queues. | |
2093 | */ | |
2094 | static void __call_rcu_nocb_enqueue(struct rcu_data *rdp, | |
2095 | struct rcu_head *rhp, | |
2096 | struct rcu_head **rhtp, | |
2097 | int rhcount, int rhcount_lazy) | |
2098 | { | |
2099 | int len; | |
2100 | struct rcu_head **old_rhpp; | |
2101 | struct task_struct *t; | |
2102 | ||
2103 | /* Enqueue the callback on the nocb list and update counts. */ | |
2104 | old_rhpp = xchg(&rdp->nocb_tail, rhtp); | |
2105 | ACCESS_ONCE(*old_rhpp) = rhp; | |
2106 | atomic_long_add(rhcount, &rdp->nocb_q_count); | |
2107 | atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy); | |
2108 | ||
2109 | /* If we are not being polled and there is a kthread, awaken it ... */ | |
2110 | t = ACCESS_ONCE(rdp->nocb_kthread); | |
2111 | if (rcu_nocb_poll | !t) | |
2112 | return; | |
2113 | len = atomic_long_read(&rdp->nocb_q_count); | |
2114 | if (old_rhpp == &rdp->nocb_head) { | |
2115 | wake_up(&rdp->nocb_wq); /* ... only if queue was empty ... */ | |
2116 | rdp->qlen_last_fqs_check = 0; | |
2117 | } else if (len > rdp->qlen_last_fqs_check + qhimark) { | |
2118 | wake_up_process(t); /* ... or if many callbacks queued. */ | |
2119 | rdp->qlen_last_fqs_check = LONG_MAX / 2; | |
2120 | } | |
2121 | return; | |
2122 | } | |
2123 | ||
2124 | /* | |
2125 | * This is a helper for __call_rcu(), which invokes this when the normal | |
2126 | * callback queue is inoperable. If this is not a no-CBs CPU, this | |
2127 | * function returns failure back to __call_rcu(), which can complain | |
2128 | * appropriately. | |
2129 | * | |
2130 | * Otherwise, this function queues the callback where the corresponding | |
2131 | * "rcuo" kthread can find it. | |
2132 | */ | |
2133 | static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, | |
2134 | bool lazy) | |
2135 | { | |
2136 | ||
d1e43fa5 | 2137 | if (!rcu_is_nocb_cpu(rdp->cpu)) |
3fbfbf7a PM |
2138 | return 0; |
2139 | __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy); | |
21e7a608 PM |
2140 | if (__is_kfree_rcu_offset((unsigned long)rhp->func)) |
2141 | trace_rcu_kfree_callback(rdp->rsp->name, rhp, | |
2142 | (unsigned long)rhp->func, | |
2143 | rdp->qlen_lazy, rdp->qlen); | |
2144 | else | |
2145 | trace_rcu_callback(rdp->rsp->name, rhp, | |
2146 | rdp->qlen_lazy, rdp->qlen); | |
3fbfbf7a PM |
2147 | return 1; |
2148 | } | |
2149 | ||
2150 | /* | |
2151 | * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is | |
2152 | * not a no-CBs CPU. | |
2153 | */ | |
2154 | static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, | |
2155 | struct rcu_data *rdp) | |
2156 | { | |
2157 | long ql = rsp->qlen; | |
2158 | long qll = rsp->qlen_lazy; | |
2159 | ||
2160 | /* If this is not a no-CBs CPU, tell the caller to do it the old way. */ | |
d1e43fa5 | 2161 | if (!rcu_is_nocb_cpu(smp_processor_id())) |
3fbfbf7a PM |
2162 | return 0; |
2163 | rsp->qlen = 0; | |
2164 | rsp->qlen_lazy = 0; | |
2165 | ||
2166 | /* First, enqueue the donelist, if any. This preserves CB ordering. */ | |
2167 | if (rsp->orphan_donelist != NULL) { | |
2168 | __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist, | |
2169 | rsp->orphan_donetail, ql, qll); | |
2170 | ql = qll = 0; | |
2171 | rsp->orphan_donelist = NULL; | |
2172 | rsp->orphan_donetail = &rsp->orphan_donelist; | |
2173 | } | |
2174 | if (rsp->orphan_nxtlist != NULL) { | |
2175 | __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist, | |
2176 | rsp->orphan_nxttail, ql, qll); | |
2177 | ql = qll = 0; | |
2178 | rsp->orphan_nxtlist = NULL; | |
2179 | rsp->orphan_nxttail = &rsp->orphan_nxtlist; | |
2180 | } | |
2181 | return 1; | |
2182 | } | |
2183 | ||
2184 | /* | |
34ed6246 PM |
2185 | * If necessary, kick off a new grace period, and either way wait |
2186 | * for a subsequent grace period to complete. | |
3fbfbf7a | 2187 | */ |
34ed6246 | 2188 | static void rcu_nocb_wait_gp(struct rcu_data *rdp) |
3fbfbf7a | 2189 | { |
34ed6246 | 2190 | unsigned long c; |
dae6e64d | 2191 | bool d; |
34ed6246 | 2192 | unsigned long flags; |
34ed6246 PM |
2193 | struct rcu_node *rnp = rdp->mynode; |
2194 | ||
2195 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
0446be48 PM |
2196 | c = rcu_start_future_gp(rnp, rdp); |
2197 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
3fbfbf7a PM |
2198 | |
2199 | /* | |
34ed6246 PM |
2200 | * Wait for the grace period. Do so interruptibly to avoid messing |
2201 | * up the load average. | |
3fbfbf7a | 2202 | */ |
f7f7bac9 | 2203 | trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait")); |
34ed6246 | 2204 | for (;;) { |
dae6e64d PM |
2205 | wait_event_interruptible( |
2206 | rnp->nocb_gp_wq[c & 0x1], | |
2207 | (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c))); | |
2208 | if (likely(d)) | |
34ed6246 | 2209 | break; |
dae6e64d | 2210 | flush_signals(current); |
f7f7bac9 | 2211 | trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait")); |
34ed6246 | 2212 | } |
f7f7bac9 | 2213 | trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait")); |
34ed6246 | 2214 | smp_mb(); /* Ensure that CB invocation happens after GP end. */ |
3fbfbf7a PM |
2215 | } |
2216 | ||
2217 | /* | |
2218 | * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes | |
2219 | * callbacks queued by the corresponding no-CBs CPU. | |
2220 | */ | |
2221 | static int rcu_nocb_kthread(void *arg) | |
2222 | { | |
2223 | int c, cl; | |
2224 | struct rcu_head *list; | |
2225 | struct rcu_head *next; | |
2226 | struct rcu_head **tail; | |
2227 | struct rcu_data *rdp = arg; | |
2228 | ||
2229 | /* Each pass through this loop invokes one batch of callbacks */ | |
2230 | for (;;) { | |
2231 | /* If not polling, wait for next batch of callbacks. */ | |
2232 | if (!rcu_nocb_poll) | |
353af9c9 | 2233 | wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head); |
3fbfbf7a PM |
2234 | list = ACCESS_ONCE(rdp->nocb_head); |
2235 | if (!list) { | |
2236 | schedule_timeout_interruptible(1); | |
353af9c9 | 2237 | flush_signals(current); |
3fbfbf7a PM |
2238 | continue; |
2239 | } | |
2240 | ||
2241 | /* | |
2242 | * Extract queued callbacks, update counts, and wait | |
2243 | * for a grace period to elapse. | |
2244 | */ | |
2245 | ACCESS_ONCE(rdp->nocb_head) = NULL; | |
2246 | tail = xchg(&rdp->nocb_tail, &rdp->nocb_head); | |
2247 | c = atomic_long_xchg(&rdp->nocb_q_count, 0); | |
2248 | cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0); | |
2249 | ACCESS_ONCE(rdp->nocb_p_count) += c; | |
2250 | ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl; | |
34ed6246 | 2251 | rcu_nocb_wait_gp(rdp); |
3fbfbf7a PM |
2252 | |
2253 | /* Each pass through the following loop invokes a callback. */ | |
2254 | trace_rcu_batch_start(rdp->rsp->name, cl, c, -1); | |
2255 | c = cl = 0; | |
2256 | while (list) { | |
2257 | next = list->next; | |
2258 | /* Wait for enqueuing to complete, if needed. */ | |
2259 | while (next == NULL && &list->next != tail) { | |
2260 | schedule_timeout_interruptible(1); | |
2261 | next = list->next; | |
2262 | } | |
2263 | debug_rcu_head_unqueue(list); | |
2264 | local_bh_disable(); | |
2265 | if (__rcu_reclaim(rdp->rsp->name, list)) | |
2266 | cl++; | |
2267 | c++; | |
2268 | local_bh_enable(); | |
2269 | list = next; | |
2270 | } | |
2271 | trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1); | |
2272 | ACCESS_ONCE(rdp->nocb_p_count) -= c; | |
2273 | ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl; | |
c635a4e1 | 2274 | rdp->n_nocbs_invoked += c; |
3fbfbf7a PM |
2275 | } |
2276 | return 0; | |
2277 | } | |
2278 | ||
2279 | /* Initialize per-rcu_data variables for no-CBs CPUs. */ | |
2280 | static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) | |
2281 | { | |
2282 | rdp->nocb_tail = &rdp->nocb_head; | |
2283 | init_waitqueue_head(&rdp->nocb_wq); | |
2284 | } | |
2285 | ||
2286 | /* Create a kthread for each RCU flavor for each no-CBs CPU. */ | |
2287 | static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp) | |
2288 | { | |
2289 | int cpu; | |
2290 | struct rcu_data *rdp; | |
2291 | struct task_struct *t; | |
2292 | ||
2293 | if (rcu_nocb_mask == NULL) | |
2294 | return; | |
2295 | for_each_cpu(cpu, rcu_nocb_mask) { | |
2296 | rdp = per_cpu_ptr(rsp->rda, cpu); | |
a4889858 PM |
2297 | t = kthread_run(rcu_nocb_kthread, rdp, |
2298 | "rcuo%c/%d", rsp->abbr, cpu); | |
3fbfbf7a PM |
2299 | BUG_ON(IS_ERR(t)); |
2300 | ACCESS_ONCE(rdp->nocb_kthread) = t; | |
2301 | } | |
2302 | } | |
2303 | ||
2304 | /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */ | |
34ed6246 | 2305 | static bool init_nocb_callback_list(struct rcu_data *rdp) |
3fbfbf7a PM |
2306 | { |
2307 | if (rcu_nocb_mask == NULL || | |
2308 | !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask)) | |
34ed6246 | 2309 | return false; |
3fbfbf7a | 2310 | rdp->nxttail[RCU_NEXT_TAIL] = NULL; |
34ed6246 | 2311 | return true; |
3fbfbf7a PM |
2312 | } |
2313 | ||
34ed6246 PM |
2314 | #else /* #ifdef CONFIG_RCU_NOCB_CPU */ |
2315 | ||
dae6e64d PM |
2316 | static int rcu_nocb_needs_gp(struct rcu_state *rsp) |
2317 | { | |
2318 | return 0; | |
3fbfbf7a PM |
2319 | } |
2320 | ||
0446be48 | 2321 | static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) |
3fbfbf7a | 2322 | { |
3fbfbf7a PM |
2323 | } |
2324 | ||
dae6e64d PM |
2325 | static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) |
2326 | { | |
2327 | } | |
2328 | ||
2329 | static void rcu_init_one_nocb(struct rcu_node *rnp) | |
2330 | { | |
2331 | } | |
3fbfbf7a | 2332 | |
3fbfbf7a PM |
2333 | static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, |
2334 | bool lazy) | |
2335 | { | |
2336 | return 0; | |
2337 | } | |
2338 | ||
2339 | static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, | |
2340 | struct rcu_data *rdp) | |
2341 | { | |
2342 | return 0; | |
2343 | } | |
2344 | ||
3fbfbf7a PM |
2345 | static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) |
2346 | { | |
2347 | } | |
2348 | ||
2349 | static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp) | |
2350 | { | |
2351 | } | |
2352 | ||
34ed6246 | 2353 | static bool init_nocb_callback_list(struct rcu_data *rdp) |
3fbfbf7a | 2354 | { |
34ed6246 | 2355 | return false; |
3fbfbf7a PM |
2356 | } |
2357 | ||
2358 | #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ | |
65d798f0 PM |
2359 | |
2360 | /* | |
2361 | * An adaptive-ticks CPU can potentially execute in kernel mode for an | |
2362 | * arbitrarily long period of time with the scheduling-clock tick turned | |
2363 | * off. RCU will be paying attention to this CPU because it is in the | |
2364 | * kernel, but the CPU cannot be guaranteed to be executing the RCU state | |
2365 | * machine because the scheduling-clock tick has been disabled. Therefore, | |
2366 | * if an adaptive-ticks CPU is failing to respond to the current grace | |
2367 | * period and has not be idle from an RCU perspective, kick it. | |
2368 | */ | |
2369 | static void rcu_kick_nohz_cpu(int cpu) | |
2370 | { | |
2371 | #ifdef CONFIG_NO_HZ_FULL | |
2372 | if (tick_nohz_full_cpu(cpu)) | |
2373 | smp_send_reschedule(cpu); | |
2374 | #endif /* #ifdef CONFIG_NO_HZ_FULL */ | |
2375 | } | |
2333210b PM |
2376 | |
2377 | ||
2378 | #ifdef CONFIG_NO_HZ_FULL_SYSIDLE | |
2379 | ||
d4bd54fb PM |
2380 | /* |
2381 | * Define RCU flavor that holds sysidle state. This needs to be the | |
2382 | * most active flavor of RCU. | |
2383 | */ | |
2384 | #ifdef CONFIG_PREEMPT_RCU | |
0edd1b17 | 2385 | static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state; |
d4bd54fb | 2386 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
0edd1b17 | 2387 | static struct rcu_state *rcu_sysidle_state = &rcu_sched_state; |
d4bd54fb PM |
2388 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
2389 | ||
0edd1b17 | 2390 | static int full_sysidle_state; /* Current system-idle state. */ |
d4bd54fb PM |
2391 | #define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */ |
2392 | #define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */ | |
2393 | #define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */ | |
2394 | #define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */ | |
2395 | #define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */ | |
2396 | ||
eb348b89 PM |
2397 | /* |
2398 | * Invoked to note exit from irq or task transition to idle. Note that | |
2399 | * usermode execution does -not- count as idle here! After all, we want | |
2400 | * to detect full-system idle states, not RCU quiescent states and grace | |
2401 | * periods. The caller must have disabled interrupts. | |
2402 | */ | |
2403 | static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq) | |
2404 | { | |
2405 | unsigned long j; | |
2406 | ||
2407 | /* Adjust nesting, check for fully idle. */ | |
2408 | if (irq) { | |
2409 | rdtp->dynticks_idle_nesting--; | |
2410 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); | |
2411 | if (rdtp->dynticks_idle_nesting != 0) | |
2412 | return; /* Still not fully idle. */ | |
2413 | } else { | |
2414 | if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) == | |
2415 | DYNTICK_TASK_NEST_VALUE) { | |
2416 | rdtp->dynticks_idle_nesting = 0; | |
2417 | } else { | |
2418 | rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE; | |
2419 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); | |
2420 | return; /* Still not fully idle. */ | |
2421 | } | |
2422 | } | |
2423 | ||
2424 | /* Record start of fully idle period. */ | |
2425 | j = jiffies; | |
2426 | ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j; | |
2427 | smp_mb__before_atomic_inc(); | |
2428 | atomic_inc(&rdtp->dynticks_idle); | |
2429 | smp_mb__after_atomic_inc(); | |
2430 | WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1); | |
2431 | } | |
2432 | ||
0edd1b17 PM |
2433 | /* |
2434 | * Unconditionally force exit from full system-idle state. This is | |
2435 | * invoked when a normal CPU exits idle, but must be called separately | |
2436 | * for the timekeeping CPU (tick_do_timer_cpu). The reason for this | |
2437 | * is that the timekeeping CPU is permitted to take scheduling-clock | |
2438 | * interrupts while the system is in system-idle state, and of course | |
2439 | * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock | |
2440 | * interrupt from any other type of interrupt. | |
2441 | */ | |
2442 | void rcu_sysidle_force_exit(void) | |
2443 | { | |
2444 | int oldstate = ACCESS_ONCE(full_sysidle_state); | |
2445 | int newoldstate; | |
2446 | ||
2447 | /* | |
2448 | * Each pass through the following loop attempts to exit full | |
2449 | * system-idle state. If contention proves to be a problem, | |
2450 | * a trylock-based contention tree could be used here. | |
2451 | */ | |
2452 | while (oldstate > RCU_SYSIDLE_SHORT) { | |
2453 | newoldstate = cmpxchg(&full_sysidle_state, | |
2454 | oldstate, RCU_SYSIDLE_NOT); | |
2455 | if (oldstate == newoldstate && | |
2456 | oldstate == RCU_SYSIDLE_FULL_NOTED) { | |
2457 | rcu_kick_nohz_cpu(tick_do_timer_cpu); | |
2458 | return; /* We cleared it, done! */ | |
2459 | } | |
2460 | oldstate = newoldstate; | |
2461 | } | |
2462 | smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */ | |
2463 | } | |
2464 | ||
eb348b89 PM |
2465 | /* |
2466 | * Invoked to note entry to irq or task transition from idle. Note that | |
2467 | * usermode execution does -not- count as idle here! The caller must | |
2468 | * have disabled interrupts. | |
2469 | */ | |
2470 | static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq) | |
2471 | { | |
2472 | /* Adjust nesting, check for already non-idle. */ | |
2473 | if (irq) { | |
2474 | rdtp->dynticks_idle_nesting++; | |
2475 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); | |
2476 | if (rdtp->dynticks_idle_nesting != 1) | |
2477 | return; /* Already non-idle. */ | |
2478 | } else { | |
2479 | /* | |
2480 | * Allow for irq misnesting. Yes, it really is possible | |
2481 | * to enter an irq handler then never leave it, and maybe | |
2482 | * also vice versa. Handle both possibilities. | |
2483 | */ | |
2484 | if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) { | |
2485 | rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE; | |
2486 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); | |
2487 | return; /* Already non-idle. */ | |
2488 | } else { | |
2489 | rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE; | |
2490 | } | |
2491 | } | |
2492 | ||
2493 | /* Record end of idle period. */ | |
2494 | smp_mb__before_atomic_inc(); | |
2495 | atomic_inc(&rdtp->dynticks_idle); | |
2496 | smp_mb__after_atomic_inc(); | |
2497 | WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1)); | |
0edd1b17 PM |
2498 | |
2499 | /* | |
2500 | * If we are the timekeeping CPU, we are permitted to be non-idle | |
2501 | * during a system-idle state. This must be the case, because | |
2502 | * the timekeeping CPU has to take scheduling-clock interrupts | |
2503 | * during the time that the system is transitioning to full | |
2504 | * system-idle state. This means that the timekeeping CPU must | |
2505 | * invoke rcu_sysidle_force_exit() directly if it does anything | |
2506 | * more than take a scheduling-clock interrupt. | |
2507 | */ | |
2508 | if (smp_processor_id() == tick_do_timer_cpu) | |
2509 | return; | |
2510 | ||
2511 | /* Update system-idle state: We are clearly no longer fully idle! */ | |
2512 | rcu_sysidle_force_exit(); | |
2513 | } | |
2514 | ||
2515 | /* | |
2516 | * Check to see if the current CPU is idle. Note that usermode execution | |
2517 | * does not count as idle. The caller must have disabled interrupts. | |
2518 | */ | |
2519 | static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, | |
2520 | unsigned long *maxj) | |
2521 | { | |
2522 | int cur; | |
2523 | unsigned long j; | |
2524 | struct rcu_dynticks *rdtp = rdp->dynticks; | |
2525 | ||
2526 | /* | |
2527 | * If some other CPU has already reported non-idle, if this is | |
2528 | * not the flavor of RCU that tracks sysidle state, or if this | |
2529 | * is an offline or the timekeeping CPU, nothing to do. | |
2530 | */ | |
2531 | if (!*isidle || rdp->rsp != rcu_sysidle_state || | |
2532 | cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu) | |
2533 | return; | |
eb75767b PM |
2534 | if (rcu_gp_in_progress(rdp->rsp)) |
2535 | WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); | |
0edd1b17 PM |
2536 | |
2537 | /* Pick up current idle and NMI-nesting counter and check. */ | |
2538 | cur = atomic_read(&rdtp->dynticks_idle); | |
2539 | if (cur & 0x1) { | |
2540 | *isidle = false; /* We are not idle! */ | |
2541 | return; | |
2542 | } | |
2543 | smp_mb(); /* Read counters before timestamps. */ | |
2544 | ||
2545 | /* Pick up timestamps. */ | |
2546 | j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies); | |
2547 | /* If this CPU entered idle more recently, update maxj timestamp. */ | |
2548 | if (ULONG_CMP_LT(*maxj, j)) | |
2549 | *maxj = j; | |
2550 | } | |
2551 | ||
2552 | /* | |
2553 | * Is this the flavor of RCU that is handling full-system idle? | |
2554 | */ | |
2555 | static bool is_sysidle_rcu_state(struct rcu_state *rsp) | |
2556 | { | |
2557 | return rsp == rcu_sysidle_state; | |
2558 | } | |
2559 | ||
eb75767b PM |
2560 | /* |
2561 | * Bind the grace-period kthread for the sysidle flavor of RCU to the | |
2562 | * timekeeping CPU. | |
2563 | */ | |
2564 | static void rcu_bind_gp_kthread(void) | |
2565 | { | |
2566 | int cpu = ACCESS_ONCE(tick_do_timer_cpu); | |
2567 | ||
2568 | if (cpu < 0 || cpu >= nr_cpu_ids) | |
2569 | return; | |
2570 | if (raw_smp_processor_id() != cpu) | |
2571 | set_cpus_allowed_ptr(current, cpumask_of(cpu)); | |
2572 | } | |
2573 | ||
0edd1b17 PM |
2574 | /* |
2575 | * Return a delay in jiffies based on the number of CPUs, rcu_node | |
2576 | * leaf fanout, and jiffies tick rate. The idea is to allow larger | |
2577 | * systems more time to transition to full-idle state in order to | |
2578 | * avoid the cache thrashing that otherwise occur on the state variable. | |
2579 | * Really small systems (less than a couple of tens of CPUs) should | |
2580 | * instead use a single global atomically incremented counter, and later | |
2581 | * versions of this will automatically reconfigure themselves accordingly. | |
2582 | */ | |
2583 | static unsigned long rcu_sysidle_delay(void) | |
2584 | { | |
2585 | if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) | |
2586 | return 0; | |
2587 | return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000); | |
2588 | } | |
2589 | ||
2590 | /* | |
2591 | * Advance the full-system-idle state. This is invoked when all of | |
2592 | * the non-timekeeping CPUs are idle. | |
2593 | */ | |
2594 | static void rcu_sysidle(unsigned long j) | |
2595 | { | |
2596 | /* Check the current state. */ | |
2597 | switch (ACCESS_ONCE(full_sysidle_state)) { | |
2598 | case RCU_SYSIDLE_NOT: | |
2599 | ||
2600 | /* First time all are idle, so note a short idle period. */ | |
2601 | ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT; | |
2602 | break; | |
2603 | ||
2604 | case RCU_SYSIDLE_SHORT: | |
2605 | ||
2606 | /* | |
2607 | * Idle for a bit, time to advance to next state? | |
2608 | * cmpxchg failure means race with non-idle, let them win. | |
2609 | */ | |
2610 | if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) | |
2611 | (void)cmpxchg(&full_sysidle_state, | |
2612 | RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG); | |
2613 | break; | |
2614 | ||
2615 | case RCU_SYSIDLE_LONG: | |
2616 | ||
2617 | /* | |
2618 | * Do an additional check pass before advancing to full. | |
2619 | * cmpxchg failure means race with non-idle, let them win. | |
2620 | */ | |
2621 | if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) | |
2622 | (void)cmpxchg(&full_sysidle_state, | |
2623 | RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL); | |
2624 | break; | |
2625 | ||
2626 | default: | |
2627 | break; | |
2628 | } | |
2629 | } | |
2630 | ||
2631 | /* | |
2632 | * Found a non-idle non-timekeeping CPU, so kick the system-idle state | |
2633 | * back to the beginning. | |
2634 | */ | |
2635 | static void rcu_sysidle_cancel(void) | |
2636 | { | |
2637 | smp_mb(); | |
2638 | ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT; | |
2639 | } | |
2640 | ||
2641 | /* | |
2642 | * Update the sysidle state based on the results of a force-quiescent-state | |
2643 | * scan of the CPUs' dyntick-idle state. | |
2644 | */ | |
2645 | static void rcu_sysidle_report(struct rcu_state *rsp, int isidle, | |
2646 | unsigned long maxj, bool gpkt) | |
2647 | { | |
2648 | if (rsp != rcu_sysidle_state) | |
2649 | return; /* Wrong flavor, ignore. */ | |
2650 | if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) | |
2651 | return; /* Running state machine from timekeeping CPU. */ | |
2652 | if (isidle) | |
2653 | rcu_sysidle(maxj); /* More idle! */ | |
2654 | else | |
2655 | rcu_sysidle_cancel(); /* Idle is over. */ | |
2656 | } | |
2657 | ||
2658 | /* | |
2659 | * Wrapper for rcu_sysidle_report() when called from the grace-period | |
2660 | * kthread's context. | |
2661 | */ | |
2662 | static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, | |
2663 | unsigned long maxj) | |
2664 | { | |
2665 | rcu_sysidle_report(rsp, isidle, maxj, true); | |
2666 | } | |
2667 | ||
2668 | /* Callback and function for forcing an RCU grace period. */ | |
2669 | struct rcu_sysidle_head { | |
2670 | struct rcu_head rh; | |
2671 | int inuse; | |
2672 | }; | |
2673 | ||
2674 | static void rcu_sysidle_cb(struct rcu_head *rhp) | |
2675 | { | |
2676 | struct rcu_sysidle_head *rshp; | |
2677 | ||
2678 | /* | |
2679 | * The following memory barrier is needed to replace the | |
2680 | * memory barriers that would normally be in the memory | |
2681 | * allocator. | |
2682 | */ | |
2683 | smp_mb(); /* grace period precedes setting inuse. */ | |
2684 | ||
2685 | rshp = container_of(rhp, struct rcu_sysidle_head, rh); | |
2686 | ACCESS_ONCE(rshp->inuse) = 0; | |
2687 | } | |
2688 | ||
2689 | /* | |
2690 | * Check to see if the system is fully idle, other than the timekeeping CPU. | |
2691 | * The caller must have disabled interrupts. | |
2692 | */ | |
2693 | bool rcu_sys_is_idle(void) | |
2694 | { | |
2695 | static struct rcu_sysidle_head rsh; | |
2696 | int rss = ACCESS_ONCE(full_sysidle_state); | |
2697 | ||
2698 | if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu)) | |
2699 | return false; | |
2700 | ||
2701 | /* Handle small-system case by doing a full scan of CPUs. */ | |
2702 | if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) { | |
2703 | int oldrss = rss - 1; | |
2704 | ||
2705 | /* | |
2706 | * One pass to advance to each state up to _FULL. | |
2707 | * Give up if any pass fails to advance the state. | |
2708 | */ | |
2709 | while (rss < RCU_SYSIDLE_FULL && oldrss < rss) { | |
2710 | int cpu; | |
2711 | bool isidle = true; | |
2712 | unsigned long maxj = jiffies - ULONG_MAX / 4; | |
2713 | struct rcu_data *rdp; | |
2714 | ||
2715 | /* Scan all the CPUs looking for nonidle CPUs. */ | |
2716 | for_each_possible_cpu(cpu) { | |
2717 | rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu); | |
2718 | rcu_sysidle_check_cpu(rdp, &isidle, &maxj); | |
2719 | if (!isidle) | |
2720 | break; | |
2721 | } | |
2722 | rcu_sysidle_report(rcu_sysidle_state, | |
2723 | isidle, maxj, false); | |
2724 | oldrss = rss; | |
2725 | rss = ACCESS_ONCE(full_sysidle_state); | |
2726 | } | |
2727 | } | |
2728 | ||
2729 | /* If this is the first observation of an idle period, record it. */ | |
2730 | if (rss == RCU_SYSIDLE_FULL) { | |
2731 | rss = cmpxchg(&full_sysidle_state, | |
2732 | RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED); | |
2733 | return rss == RCU_SYSIDLE_FULL; | |
2734 | } | |
2735 | ||
2736 | smp_mb(); /* ensure rss load happens before later caller actions. */ | |
2737 | ||
2738 | /* If already fully idle, tell the caller (in case of races). */ | |
2739 | if (rss == RCU_SYSIDLE_FULL_NOTED) | |
2740 | return true; | |
2741 | ||
2742 | /* | |
2743 | * If we aren't there yet, and a grace period is not in flight, | |
2744 | * initiate a grace period. Either way, tell the caller that | |
2745 | * we are not there yet. We use an xchg() rather than an assignment | |
2746 | * to make up for the memory barriers that would otherwise be | |
2747 | * provided by the memory allocator. | |
2748 | */ | |
2749 | if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL && | |
2750 | !rcu_gp_in_progress(rcu_sysidle_state) && | |
2751 | !rsh.inuse && xchg(&rsh.inuse, 1) == 0) | |
2752 | call_rcu(&rsh.rh, rcu_sysidle_cb); | |
2753 | return false; | |
eb348b89 PM |
2754 | } |
2755 | ||
2333210b PM |
2756 | /* |
2757 | * Initialize dynticks sysidle state for CPUs coming online. | |
2758 | */ | |
2759 | static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) | |
2760 | { | |
2761 | rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE; | |
2762 | } | |
2763 | ||
2764 | #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ | |
2765 | ||
eb348b89 PM |
2766 | static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq) |
2767 | { | |
2768 | } | |
2769 | ||
2770 | static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq) | |
2771 | { | |
2772 | } | |
2773 | ||
0edd1b17 PM |
2774 | static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, |
2775 | unsigned long *maxj) | |
2776 | { | |
2777 | } | |
2778 | ||
2779 | static bool is_sysidle_rcu_state(struct rcu_state *rsp) | |
2780 | { | |
2781 | return false; | |
2782 | } | |
2783 | ||
eb75767b PM |
2784 | static void rcu_bind_gp_kthread(void) |
2785 | { | |
2786 | } | |
2787 | ||
0edd1b17 PM |
2788 | static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, |
2789 | unsigned long maxj) | |
2790 | { | |
2791 | } | |
2792 | ||
2333210b PM |
2793 | static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) |
2794 | { | |
2795 | } | |
2796 | ||
2797 | #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ |