Commit | Line | Data |
---|---|---|
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> |
f41d911f | 28 | |
5b61b0ba MG |
29 | #define RCU_KTHREAD_PRIO 1 |
30 | ||
31 | #ifdef CONFIG_RCU_BOOST | |
32 | #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO | |
33 | #else | |
34 | #define RCU_BOOST_PRIO RCU_KTHREAD_PRIO | |
35 | #endif | |
36 | ||
26845c28 PM |
37 | /* |
38 | * Check the RCU kernel configuration parameters and print informative | |
39 | * messages about anything out of the ordinary. If you like #ifdef, you | |
40 | * will love this function. | |
41 | */ | |
42 | static void __init rcu_bootup_announce_oddness(void) | |
43 | { | |
44 | #ifdef CONFIG_RCU_TRACE | |
45 | printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n"); | |
46 | #endif | |
47 | #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32) | |
48 | printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n", | |
49 | CONFIG_RCU_FANOUT); | |
50 | #endif | |
51 | #ifdef CONFIG_RCU_FANOUT_EXACT | |
52 | printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n"); | |
53 | #endif | |
54 | #ifdef CONFIG_RCU_FAST_NO_HZ | |
55 | printk(KERN_INFO | |
56 | "\tRCU dyntick-idle grace-period acceleration is enabled.\n"); | |
57 | #endif | |
58 | #ifdef CONFIG_PROVE_RCU | |
59 | printk(KERN_INFO "\tRCU lockdep checking is enabled.\n"); | |
60 | #endif | |
61 | #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE | |
62 | printk(KERN_INFO "\tRCU torture testing starts during boot.\n"); | |
63 | #endif | |
81a294c4 | 64 | #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE) |
a858af28 PM |
65 | printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n"); |
66 | #endif | |
67 | #if defined(CONFIG_RCU_CPU_STALL_INFO) | |
68 | printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n"); | |
26845c28 PM |
69 | #endif |
70 | #if NUM_RCU_LVL_4 != 0 | |
cc5df65b | 71 | printk(KERN_INFO "\tFour-level hierarchy is enabled.\n"); |
26845c28 | 72 | #endif |
f885b7f2 PM |
73 | if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF) |
74 | printk(KERN_INFO "\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf); | |
cca6f393 PM |
75 | if (nr_cpu_ids != NR_CPUS) |
76 | printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids); | |
26845c28 PM |
77 | } |
78 | ||
f41d911f PM |
79 | #ifdef CONFIG_TREE_PREEMPT_RCU |
80 | ||
037b64ed PM |
81 | struct rcu_state rcu_preempt_state = |
82 | RCU_STATE_INITIALIZER(rcu_preempt, call_rcu); | |
f41d911f | 83 | DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data); |
27f4d280 | 84 | static struct rcu_state *rcu_state = &rcu_preempt_state; |
f41d911f | 85 | |
d9a3da06 PM |
86 | static int rcu_preempted_readers_exp(struct rcu_node *rnp); |
87 | ||
f41d911f PM |
88 | /* |
89 | * Tell them what RCU they are running. | |
90 | */ | |
0e0fc1c2 | 91 | static void __init rcu_bootup_announce(void) |
f41d911f | 92 | { |
6cc68793 | 93 | printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n"); |
26845c28 | 94 | rcu_bootup_announce_oddness(); |
f41d911f PM |
95 | } |
96 | ||
97 | /* | |
98 | * Return the number of RCU-preempt batches processed thus far | |
99 | * for debug and statistics. | |
100 | */ | |
101 | long rcu_batches_completed_preempt(void) | |
102 | { | |
103 | return rcu_preempt_state.completed; | |
104 | } | |
105 | EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt); | |
106 | ||
107 | /* | |
108 | * Return the number of RCU batches processed thus far for debug & stats. | |
109 | */ | |
110 | long rcu_batches_completed(void) | |
111 | { | |
112 | return rcu_batches_completed_preempt(); | |
113 | } | |
114 | EXPORT_SYMBOL_GPL(rcu_batches_completed); | |
115 | ||
bf66f18e PM |
116 | /* |
117 | * Force a quiescent state for preemptible RCU. | |
118 | */ | |
119 | void rcu_force_quiescent_state(void) | |
120 | { | |
121 | force_quiescent_state(&rcu_preempt_state, 0); | |
122 | } | |
123 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); | |
124 | ||
f41d911f | 125 | /* |
6cc68793 | 126 | * Record a preemptible-RCU quiescent state for the specified CPU. Note |
f41d911f PM |
127 | * that this just means that the task currently running on the CPU is |
128 | * not in a quiescent state. There might be any number of tasks blocked | |
129 | * while in an RCU read-side critical section. | |
25502a6c PM |
130 | * |
131 | * Unlike the other rcu_*_qs() functions, callers to this function | |
132 | * must disable irqs in order to protect the assignment to | |
133 | * ->rcu_read_unlock_special. | |
f41d911f | 134 | */ |
c3422bea | 135 | static void rcu_preempt_qs(int cpu) |
f41d911f PM |
136 | { |
137 | struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); | |
25502a6c | 138 | |
e4cc1f22 | 139 | rdp->passed_quiesce_gpnum = rdp->gpnum; |
c3422bea | 140 | barrier(); |
e4cc1f22 | 141 | if (rdp->passed_quiesce == 0) |
d4c08f2a | 142 | trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs"); |
e4cc1f22 | 143 | rdp->passed_quiesce = 1; |
25502a6c | 144 | current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; |
f41d911f PM |
145 | } |
146 | ||
147 | /* | |
c3422bea PM |
148 | * We have entered the scheduler, and the current task might soon be |
149 | * context-switched away from. If this task is in an RCU read-side | |
150 | * critical section, we will no longer be able to rely on the CPU to | |
12f5f524 PM |
151 | * record that fact, so we enqueue the task on the blkd_tasks list. |
152 | * The task will dequeue itself when it exits the outermost enclosing | |
153 | * RCU read-side critical section. Therefore, the current grace period | |
154 | * cannot be permitted to complete until the blkd_tasks list entries | |
155 | * predating the current grace period drain, in other words, until | |
156 | * rnp->gp_tasks becomes NULL. | |
c3422bea PM |
157 | * |
158 | * Caller must disable preemption. | |
f41d911f | 159 | */ |
cba6d0d6 | 160 | static void rcu_preempt_note_context_switch(int cpu) |
f41d911f PM |
161 | { |
162 | struct task_struct *t = current; | |
c3422bea | 163 | unsigned long flags; |
f41d911f PM |
164 | struct rcu_data *rdp; |
165 | struct rcu_node *rnp; | |
166 | ||
10f39bb1 | 167 | if (t->rcu_read_lock_nesting > 0 && |
f41d911f PM |
168 | (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { |
169 | ||
170 | /* Possibly blocking in an RCU read-side critical section. */ | |
cba6d0d6 | 171 | rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu); |
f41d911f | 172 | rnp = rdp->mynode; |
1304afb2 | 173 | raw_spin_lock_irqsave(&rnp->lock, flags); |
f41d911f | 174 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; |
86848966 | 175 | t->rcu_blocked_node = rnp; |
f41d911f PM |
176 | |
177 | /* | |
178 | * If this CPU has already checked in, then this task | |
179 | * will hold up the next grace period rather than the | |
180 | * current grace period. Queue the task accordingly. | |
181 | * If the task is queued for the current grace period | |
182 | * (i.e., this CPU has not yet passed through a quiescent | |
183 | * state for the current grace period), then as long | |
184 | * as that task remains queued, the current grace period | |
12f5f524 PM |
185 | * cannot end. Note that there is some uncertainty as |
186 | * to exactly when the current grace period started. | |
187 | * We take a conservative approach, which can result | |
188 | * in unnecessarily waiting on tasks that started very | |
189 | * slightly after the current grace period began. C'est | |
190 | * la vie!!! | |
b0e165c0 PM |
191 | * |
192 | * But first, note that the current CPU must still be | |
193 | * on line! | |
f41d911f | 194 | */ |
b0e165c0 | 195 | WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); |
e7d8842e | 196 | WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); |
12f5f524 PM |
197 | if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) { |
198 | list_add(&t->rcu_node_entry, rnp->gp_tasks->prev); | |
199 | rnp->gp_tasks = &t->rcu_node_entry; | |
27f4d280 PM |
200 | #ifdef CONFIG_RCU_BOOST |
201 | if (rnp->boost_tasks != NULL) | |
202 | rnp->boost_tasks = rnp->gp_tasks; | |
203 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
12f5f524 PM |
204 | } else { |
205 | list_add(&t->rcu_node_entry, &rnp->blkd_tasks); | |
206 | if (rnp->qsmask & rdp->grpmask) | |
207 | rnp->gp_tasks = &t->rcu_node_entry; | |
208 | } | |
d4c08f2a PM |
209 | trace_rcu_preempt_task(rdp->rsp->name, |
210 | t->pid, | |
211 | (rnp->qsmask & rdp->grpmask) | |
212 | ? rnp->gpnum | |
213 | : rnp->gpnum + 1); | |
1304afb2 | 214 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
10f39bb1 PM |
215 | } else if (t->rcu_read_lock_nesting < 0 && |
216 | t->rcu_read_unlock_special) { | |
217 | ||
218 | /* | |
219 | * Complete exit from RCU read-side critical section on | |
220 | * behalf of preempted instance of __rcu_read_unlock(). | |
221 | */ | |
222 | rcu_read_unlock_special(t); | |
f41d911f PM |
223 | } |
224 | ||
225 | /* | |
226 | * Either we were not in an RCU read-side critical section to | |
227 | * begin with, or we have now recorded that critical section | |
228 | * globally. Either way, we can now note a quiescent state | |
229 | * for this CPU. Again, if we were in an RCU read-side critical | |
230 | * section, and if that critical section was blocking the current | |
231 | * grace period, then the fact that the task has been enqueued | |
232 | * means that we continue to block the current grace period. | |
233 | */ | |
e7d8842e | 234 | local_irq_save(flags); |
cba6d0d6 | 235 | rcu_preempt_qs(cpu); |
e7d8842e | 236 | local_irq_restore(flags); |
f41d911f PM |
237 | } |
238 | ||
fc2219d4 PM |
239 | /* |
240 | * Check for preempted RCU readers blocking the current grace period | |
241 | * for the specified rcu_node structure. If the caller needs a reliable | |
242 | * answer, it must hold the rcu_node's ->lock. | |
243 | */ | |
27f4d280 | 244 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 | 245 | { |
12f5f524 | 246 | return rnp->gp_tasks != NULL; |
fc2219d4 PM |
247 | } |
248 | ||
b668c9cf PM |
249 | /* |
250 | * Record a quiescent state for all tasks that were previously queued | |
251 | * on the specified rcu_node structure and that were blocking the current | |
252 | * RCU grace period. The caller must hold the specified rnp->lock with | |
253 | * irqs disabled, and this lock is released upon return, but irqs remain | |
254 | * disabled. | |
255 | */ | |
d3f6bad3 | 256 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
b668c9cf PM |
257 | __releases(rnp->lock) |
258 | { | |
259 | unsigned long mask; | |
260 | struct rcu_node *rnp_p; | |
261 | ||
27f4d280 | 262 | if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { |
1304afb2 | 263 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b668c9cf PM |
264 | return; /* Still need more quiescent states! */ |
265 | } | |
266 | ||
267 | rnp_p = rnp->parent; | |
268 | if (rnp_p == NULL) { | |
269 | /* | |
270 | * Either there is only one rcu_node in the tree, | |
271 | * or tasks were kicked up to root rcu_node due to | |
272 | * CPUs going offline. | |
273 | */ | |
d3f6bad3 | 274 | rcu_report_qs_rsp(&rcu_preempt_state, flags); |
b668c9cf PM |
275 | return; |
276 | } | |
277 | ||
278 | /* Report up the rest of the hierarchy. */ | |
279 | mask = rnp->grpmask; | |
1304afb2 PM |
280 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
281 | raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */ | |
d3f6bad3 | 282 | rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags); |
b668c9cf PM |
283 | } |
284 | ||
12f5f524 PM |
285 | /* |
286 | * Advance a ->blkd_tasks-list pointer to the next entry, instead | |
287 | * returning NULL if at the end of the list. | |
288 | */ | |
289 | static struct list_head *rcu_next_node_entry(struct task_struct *t, | |
290 | struct rcu_node *rnp) | |
291 | { | |
292 | struct list_head *np; | |
293 | ||
294 | np = t->rcu_node_entry.next; | |
295 | if (np == &rnp->blkd_tasks) | |
296 | np = NULL; | |
297 | return np; | |
298 | } | |
299 | ||
b668c9cf PM |
300 | /* |
301 | * Handle special cases during rcu_read_unlock(), such as needing to | |
302 | * notify RCU core processing or task having blocked during the RCU | |
303 | * read-side critical section. | |
304 | */ | |
2a3fa843 | 305 | void rcu_read_unlock_special(struct task_struct *t) |
f41d911f PM |
306 | { |
307 | int empty; | |
d9a3da06 | 308 | int empty_exp; |
389abd48 | 309 | int empty_exp_now; |
f41d911f | 310 | unsigned long flags; |
12f5f524 | 311 | struct list_head *np; |
82e78d80 PM |
312 | #ifdef CONFIG_RCU_BOOST |
313 | struct rt_mutex *rbmp = NULL; | |
314 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
f41d911f PM |
315 | struct rcu_node *rnp; |
316 | int special; | |
317 | ||
318 | /* NMI handlers cannot block and cannot safely manipulate state. */ | |
319 | if (in_nmi()) | |
320 | return; | |
321 | ||
322 | local_irq_save(flags); | |
323 | ||
324 | /* | |
325 | * If RCU core is waiting for this CPU to exit critical section, | |
326 | * let it know that we have done so. | |
327 | */ | |
328 | special = t->rcu_read_unlock_special; | |
329 | if (special & RCU_READ_UNLOCK_NEED_QS) { | |
c3422bea | 330 | rcu_preempt_qs(smp_processor_id()); |
f41d911f PM |
331 | } |
332 | ||
333 | /* Hardware IRQ handlers cannot block. */ | |
ec433f0c | 334 | if (in_irq() || in_serving_softirq()) { |
f41d911f PM |
335 | local_irq_restore(flags); |
336 | return; | |
337 | } | |
338 | ||
339 | /* Clean up if blocked during RCU read-side critical section. */ | |
340 | if (special & RCU_READ_UNLOCK_BLOCKED) { | |
341 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; | |
342 | ||
dd5d19ba PM |
343 | /* |
344 | * Remove this task from the list it blocked on. The | |
345 | * task can migrate while we acquire the lock, but at | |
346 | * most one time. So at most two passes through loop. | |
347 | */ | |
348 | for (;;) { | |
86848966 | 349 | rnp = t->rcu_blocked_node; |
1304afb2 | 350 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
86848966 | 351 | if (rnp == t->rcu_blocked_node) |
dd5d19ba | 352 | break; |
1304afb2 | 353 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
dd5d19ba | 354 | } |
27f4d280 | 355 | empty = !rcu_preempt_blocked_readers_cgp(rnp); |
d9a3da06 PM |
356 | empty_exp = !rcu_preempted_readers_exp(rnp); |
357 | smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ | |
12f5f524 | 358 | np = rcu_next_node_entry(t, rnp); |
f41d911f | 359 | list_del_init(&t->rcu_node_entry); |
82e78d80 | 360 | t->rcu_blocked_node = NULL; |
d4c08f2a PM |
361 | trace_rcu_unlock_preempted_task("rcu_preempt", |
362 | rnp->gpnum, t->pid); | |
12f5f524 PM |
363 | if (&t->rcu_node_entry == rnp->gp_tasks) |
364 | rnp->gp_tasks = np; | |
365 | if (&t->rcu_node_entry == rnp->exp_tasks) | |
366 | rnp->exp_tasks = np; | |
27f4d280 PM |
367 | #ifdef CONFIG_RCU_BOOST |
368 | if (&t->rcu_node_entry == rnp->boost_tasks) | |
369 | rnp->boost_tasks = np; | |
82e78d80 PM |
370 | /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */ |
371 | if (t->rcu_boost_mutex) { | |
372 | rbmp = t->rcu_boost_mutex; | |
373 | t->rcu_boost_mutex = NULL; | |
7765be2f | 374 | } |
27f4d280 | 375 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
f41d911f PM |
376 | |
377 | /* | |
378 | * If this was the last task on the current list, and if | |
379 | * we aren't waiting on any CPUs, report the quiescent state. | |
389abd48 PM |
380 | * Note that rcu_report_unblock_qs_rnp() releases rnp->lock, |
381 | * so we must take a snapshot of the expedited state. | |
f41d911f | 382 | */ |
389abd48 | 383 | empty_exp_now = !rcu_preempted_readers_exp(rnp); |
d4c08f2a PM |
384 | if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) { |
385 | trace_rcu_quiescent_state_report("preempt_rcu", | |
386 | rnp->gpnum, | |
387 | 0, rnp->qsmask, | |
388 | rnp->level, | |
389 | rnp->grplo, | |
390 | rnp->grphi, | |
391 | !!rnp->gp_tasks); | |
d3f6bad3 | 392 | rcu_report_unblock_qs_rnp(rnp, flags); |
c701d5d9 | 393 | } else { |
d4c08f2a | 394 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
c701d5d9 | 395 | } |
d9a3da06 | 396 | |
27f4d280 PM |
397 | #ifdef CONFIG_RCU_BOOST |
398 | /* Unboost if we were boosted. */ | |
82e78d80 PM |
399 | if (rbmp) |
400 | rt_mutex_unlock(rbmp); | |
27f4d280 PM |
401 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
402 | ||
d9a3da06 PM |
403 | /* |
404 | * If this was the last task on the expedited lists, | |
405 | * then we need to report up the rcu_node hierarchy. | |
406 | */ | |
389abd48 | 407 | if (!empty_exp && empty_exp_now) |
b40d293e | 408 | rcu_report_exp_rnp(&rcu_preempt_state, rnp, true); |
b668c9cf PM |
409 | } else { |
410 | local_irq_restore(flags); | |
f41d911f | 411 | } |
f41d911f PM |
412 | } |
413 | ||
1ed509a2 PM |
414 | #ifdef CONFIG_RCU_CPU_STALL_VERBOSE |
415 | ||
416 | /* | |
417 | * Dump detailed information for all tasks blocking the current RCU | |
418 | * grace period on the specified rcu_node structure. | |
419 | */ | |
420 | static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) | |
421 | { | |
422 | unsigned long flags; | |
1ed509a2 PM |
423 | struct task_struct *t; |
424 | ||
27f4d280 | 425 | if (!rcu_preempt_blocked_readers_cgp(rnp)) |
12f5f524 PM |
426 | return; |
427 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
428 | t = list_entry(rnp->gp_tasks, | |
429 | struct task_struct, rcu_node_entry); | |
430 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) | |
431 | sched_show_task(t); | |
432 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
1ed509a2 PM |
433 | } |
434 | ||
435 | /* | |
436 | * Dump detailed information for all tasks blocking the current RCU | |
437 | * grace period. | |
438 | */ | |
439 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
440 | { | |
441 | struct rcu_node *rnp = rcu_get_root(rsp); | |
442 | ||
443 | rcu_print_detail_task_stall_rnp(rnp); | |
444 | rcu_for_each_leaf_node(rsp, rnp) | |
445 | rcu_print_detail_task_stall_rnp(rnp); | |
446 | } | |
447 | ||
448 | #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ | |
449 | ||
450 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
451 | { | |
452 | } | |
453 | ||
454 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ | |
455 | ||
a858af28 PM |
456 | #ifdef CONFIG_RCU_CPU_STALL_INFO |
457 | ||
458 | static void rcu_print_task_stall_begin(struct rcu_node *rnp) | |
459 | { | |
460 | printk(KERN_ERR "\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", | |
461 | rnp->level, rnp->grplo, rnp->grphi); | |
462 | } | |
463 | ||
464 | static void rcu_print_task_stall_end(void) | |
465 | { | |
466 | printk(KERN_CONT "\n"); | |
467 | } | |
468 | ||
469 | #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ | |
470 | ||
471 | static void rcu_print_task_stall_begin(struct rcu_node *rnp) | |
472 | { | |
473 | } | |
474 | ||
475 | static void rcu_print_task_stall_end(void) | |
476 | { | |
477 | } | |
478 | ||
479 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ | |
480 | ||
f41d911f PM |
481 | /* |
482 | * Scan the current list of tasks blocked within RCU read-side critical | |
483 | * sections, printing out the tid of each. | |
484 | */ | |
9bc8b558 | 485 | static int rcu_print_task_stall(struct rcu_node *rnp) |
f41d911f | 486 | { |
f41d911f | 487 | struct task_struct *t; |
9bc8b558 | 488 | int ndetected = 0; |
f41d911f | 489 | |
27f4d280 | 490 | if (!rcu_preempt_blocked_readers_cgp(rnp)) |
9bc8b558 | 491 | return 0; |
a858af28 | 492 | rcu_print_task_stall_begin(rnp); |
12f5f524 PM |
493 | t = list_entry(rnp->gp_tasks, |
494 | struct task_struct, rcu_node_entry); | |
9bc8b558 | 495 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { |
a858af28 | 496 | printk(KERN_CONT " P%d", t->pid); |
9bc8b558 PM |
497 | ndetected++; |
498 | } | |
a858af28 | 499 | rcu_print_task_stall_end(); |
9bc8b558 | 500 | return ndetected; |
f41d911f PM |
501 | } |
502 | ||
b0e165c0 PM |
503 | /* |
504 | * Check that the list of blocked tasks for the newly completed grace | |
505 | * period is in fact empty. It is a serious bug to complete a grace | |
506 | * period that still has RCU readers blocked! This function must be | |
507 | * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock | |
508 | * must be held by the caller. | |
12f5f524 PM |
509 | * |
510 | * Also, if there are blocked tasks on the list, they automatically | |
511 | * block the newly created grace period, so set up ->gp_tasks accordingly. | |
b0e165c0 PM |
512 | */ |
513 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
514 | { | |
27f4d280 | 515 | WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); |
12f5f524 PM |
516 | if (!list_empty(&rnp->blkd_tasks)) |
517 | rnp->gp_tasks = rnp->blkd_tasks.next; | |
28ecd580 | 518 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
519 | } |
520 | ||
33f76148 PM |
521 | #ifdef CONFIG_HOTPLUG_CPU |
522 | ||
dd5d19ba PM |
523 | /* |
524 | * Handle tasklist migration for case in which all CPUs covered by the | |
525 | * specified rcu_node have gone offline. Move them up to the root | |
526 | * rcu_node. The reason for not just moving them to the immediate | |
527 | * parent is to remove the need for rcu_read_unlock_special() to | |
528 | * make more than two attempts to acquire the target rcu_node's lock. | |
b668c9cf PM |
529 | * Returns true if there were tasks blocking the current RCU grace |
530 | * period. | |
dd5d19ba | 531 | * |
237c80c5 PM |
532 | * Returns 1 if there was previously a task blocking the current grace |
533 | * period on the specified rcu_node structure. | |
534 | * | |
dd5d19ba PM |
535 | * The caller must hold rnp->lock with irqs disabled. |
536 | */ | |
237c80c5 PM |
537 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
538 | struct rcu_node *rnp, | |
539 | struct rcu_data *rdp) | |
dd5d19ba | 540 | { |
dd5d19ba PM |
541 | struct list_head *lp; |
542 | struct list_head *lp_root; | |
d9a3da06 | 543 | int retval = 0; |
dd5d19ba | 544 | struct rcu_node *rnp_root = rcu_get_root(rsp); |
12f5f524 | 545 | struct task_struct *t; |
dd5d19ba | 546 | |
86848966 PM |
547 | if (rnp == rnp_root) { |
548 | WARN_ONCE(1, "Last CPU thought to be offlined?"); | |
237c80c5 | 549 | return 0; /* Shouldn't happen: at least one CPU online. */ |
86848966 | 550 | } |
12f5f524 PM |
551 | |
552 | /* If we are on an internal node, complain bitterly. */ | |
553 | WARN_ON_ONCE(rnp != rdp->mynode); | |
dd5d19ba PM |
554 | |
555 | /* | |
12f5f524 PM |
556 | * Move tasks up to root rcu_node. Don't try to get fancy for |
557 | * this corner-case operation -- just put this node's tasks | |
558 | * at the head of the root node's list, and update the root node's | |
559 | * ->gp_tasks and ->exp_tasks pointers to those of this node's, | |
560 | * if non-NULL. This might result in waiting for more tasks than | |
561 | * absolutely necessary, but this is a good performance/complexity | |
562 | * tradeoff. | |
dd5d19ba | 563 | */ |
2036d94a | 564 | if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0) |
d9a3da06 PM |
565 | retval |= RCU_OFL_TASKS_NORM_GP; |
566 | if (rcu_preempted_readers_exp(rnp)) | |
567 | retval |= RCU_OFL_TASKS_EXP_GP; | |
12f5f524 PM |
568 | lp = &rnp->blkd_tasks; |
569 | lp_root = &rnp_root->blkd_tasks; | |
570 | while (!list_empty(lp)) { | |
571 | t = list_entry(lp->next, typeof(*t), rcu_node_entry); | |
572 | raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ | |
573 | list_del(&t->rcu_node_entry); | |
574 | t->rcu_blocked_node = rnp_root; | |
575 | list_add(&t->rcu_node_entry, lp_root); | |
576 | if (&t->rcu_node_entry == rnp->gp_tasks) | |
577 | rnp_root->gp_tasks = rnp->gp_tasks; | |
578 | if (&t->rcu_node_entry == rnp->exp_tasks) | |
579 | rnp_root->exp_tasks = rnp->exp_tasks; | |
27f4d280 PM |
580 | #ifdef CONFIG_RCU_BOOST |
581 | if (&t->rcu_node_entry == rnp->boost_tasks) | |
582 | rnp_root->boost_tasks = rnp->boost_tasks; | |
583 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
12f5f524 | 584 | raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ |
dd5d19ba | 585 | } |
27f4d280 PM |
586 | |
587 | #ifdef CONFIG_RCU_BOOST | |
588 | /* In case root is being boosted and leaf is not. */ | |
589 | raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ | |
590 | if (rnp_root->boost_tasks != NULL && | |
591 | rnp_root->boost_tasks != rnp_root->gp_tasks) | |
592 | rnp_root->boost_tasks = rnp_root->gp_tasks; | |
593 | raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ | |
594 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
595 | ||
12f5f524 PM |
596 | rnp->gp_tasks = NULL; |
597 | rnp->exp_tasks = NULL; | |
237c80c5 | 598 | return retval; |
dd5d19ba PM |
599 | } |
600 | ||
e5601400 PM |
601 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
602 | ||
f41d911f PM |
603 | /* |
604 | * Check for a quiescent state from the current CPU. When a task blocks, | |
605 | * the task is recorded in the corresponding CPU's rcu_node structure, | |
606 | * which is checked elsewhere. | |
607 | * | |
608 | * Caller must disable hard irqs. | |
609 | */ | |
610 | static void rcu_preempt_check_callbacks(int cpu) | |
611 | { | |
612 | struct task_struct *t = current; | |
613 | ||
614 | if (t->rcu_read_lock_nesting == 0) { | |
c3422bea | 615 | rcu_preempt_qs(cpu); |
f41d911f PM |
616 | return; |
617 | } | |
10f39bb1 PM |
618 | if (t->rcu_read_lock_nesting > 0 && |
619 | per_cpu(rcu_preempt_data, cpu).qs_pending) | |
c3422bea | 620 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; |
f41d911f PM |
621 | } |
622 | ||
a46e0899 PM |
623 | #ifdef CONFIG_RCU_BOOST |
624 | ||
09223371 SL |
625 | static void rcu_preempt_do_callbacks(void) |
626 | { | |
627 | rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data)); | |
628 | } | |
629 | ||
a46e0899 PM |
630 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
631 | ||
f41d911f | 632 | /* |
6cc68793 | 633 | * Queue a preemptible-RCU callback for invocation after a grace period. |
f41d911f PM |
634 | */ |
635 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) | |
636 | { | |
486e2593 | 637 | __call_rcu(head, func, &rcu_preempt_state, 0); |
f41d911f PM |
638 | } |
639 | EXPORT_SYMBOL_GPL(call_rcu); | |
640 | ||
486e2593 PM |
641 | /* |
642 | * Queue an RCU callback for lazy invocation after a grace period. | |
643 | * This will likely be later named something like "call_rcu_lazy()", | |
644 | * but this change will require some way of tagging the lazy RCU | |
645 | * callbacks in the list of pending callbacks. Until then, this | |
646 | * function may only be called from __kfree_rcu(). | |
647 | */ | |
648 | void kfree_call_rcu(struct rcu_head *head, | |
649 | void (*func)(struct rcu_head *rcu)) | |
650 | { | |
651 | __call_rcu(head, func, &rcu_preempt_state, 1); | |
652 | } | |
653 | EXPORT_SYMBOL_GPL(kfree_call_rcu); | |
654 | ||
6ebb237b PM |
655 | /** |
656 | * synchronize_rcu - wait until a grace period has elapsed. | |
657 | * | |
658 | * Control will return to the caller some time after a full grace | |
659 | * period has elapsed, in other words after all currently executing RCU | |
77d8485a PM |
660 | * read-side critical sections have completed. Note, however, that |
661 | * upon return from synchronize_rcu(), the caller might well be executing | |
662 | * concurrently with new RCU read-side critical sections that began while | |
663 | * synchronize_rcu() was waiting. RCU read-side critical sections are | |
664 | * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. | |
6ebb237b PM |
665 | */ |
666 | void synchronize_rcu(void) | |
667 | { | |
fe15d706 PM |
668 | rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && |
669 | !lock_is_held(&rcu_lock_map) && | |
670 | !lock_is_held(&rcu_sched_lock_map), | |
671 | "Illegal synchronize_rcu() in RCU read-side critical section"); | |
6ebb237b PM |
672 | if (!rcu_scheduler_active) |
673 | return; | |
2c42818e | 674 | wait_rcu_gp(call_rcu); |
6ebb237b PM |
675 | } |
676 | EXPORT_SYMBOL_GPL(synchronize_rcu); | |
677 | ||
d9a3da06 PM |
678 | static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); |
679 | static long sync_rcu_preempt_exp_count; | |
680 | static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); | |
681 | ||
682 | /* | |
683 | * Return non-zero if there are any tasks in RCU read-side critical | |
684 | * sections blocking the current preemptible-RCU expedited grace period. | |
685 | * If there is no preemptible-RCU expedited grace period currently in | |
686 | * progress, returns zero unconditionally. | |
687 | */ | |
688 | static int rcu_preempted_readers_exp(struct rcu_node *rnp) | |
689 | { | |
12f5f524 | 690 | return rnp->exp_tasks != NULL; |
d9a3da06 PM |
691 | } |
692 | ||
693 | /* | |
694 | * return non-zero if there is no RCU expedited grace period in progress | |
695 | * for the specified rcu_node structure, in other words, if all CPUs and | |
696 | * tasks covered by the specified rcu_node structure have done their bit | |
697 | * for the current expedited grace period. Works only for preemptible | |
698 | * RCU -- other RCU implementation use other means. | |
699 | * | |
700 | * Caller must hold sync_rcu_preempt_exp_mutex. | |
701 | */ | |
702 | static int sync_rcu_preempt_exp_done(struct rcu_node *rnp) | |
703 | { | |
704 | return !rcu_preempted_readers_exp(rnp) && | |
705 | ACCESS_ONCE(rnp->expmask) == 0; | |
706 | } | |
707 | ||
708 | /* | |
709 | * Report the exit from RCU read-side critical section for the last task | |
710 | * that queued itself during or before the current expedited preemptible-RCU | |
711 | * grace period. This event is reported either to the rcu_node structure on | |
712 | * which the task was queued or to one of that rcu_node structure's ancestors, | |
713 | * recursively up the tree. (Calm down, calm down, we do the recursion | |
714 | * iteratively!) | |
715 | * | |
b40d293e TG |
716 | * Most callers will set the "wake" flag, but the task initiating the |
717 | * expedited grace period need not wake itself. | |
718 | * | |
d9a3da06 PM |
719 | * Caller must hold sync_rcu_preempt_exp_mutex. |
720 | */ | |
b40d293e TG |
721 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, |
722 | bool wake) | |
d9a3da06 PM |
723 | { |
724 | unsigned long flags; | |
725 | unsigned long mask; | |
726 | ||
1304afb2 | 727 | raw_spin_lock_irqsave(&rnp->lock, flags); |
d9a3da06 | 728 | for (;;) { |
131906b0 PM |
729 | if (!sync_rcu_preempt_exp_done(rnp)) { |
730 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
d9a3da06 | 731 | break; |
131906b0 | 732 | } |
d9a3da06 | 733 | if (rnp->parent == NULL) { |
131906b0 | 734 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b40d293e TG |
735 | if (wake) |
736 | wake_up(&sync_rcu_preempt_exp_wq); | |
d9a3da06 PM |
737 | break; |
738 | } | |
739 | mask = rnp->grpmask; | |
1304afb2 | 740 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ |
d9a3da06 | 741 | rnp = rnp->parent; |
1304afb2 | 742 | raw_spin_lock(&rnp->lock); /* irqs already disabled */ |
d9a3da06 PM |
743 | rnp->expmask &= ~mask; |
744 | } | |
d9a3da06 PM |
745 | } |
746 | ||
747 | /* | |
748 | * Snapshot the tasks blocking the newly started preemptible-RCU expedited | |
749 | * grace period for the specified rcu_node structure. If there are no such | |
750 | * tasks, report it up the rcu_node hierarchy. | |
751 | * | |
752 | * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock. | |
753 | */ | |
754 | static void | |
755 | sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) | |
756 | { | |
1217ed1b | 757 | unsigned long flags; |
12f5f524 | 758 | int must_wait = 0; |
d9a3da06 | 759 | |
1217ed1b | 760 | raw_spin_lock_irqsave(&rnp->lock, flags); |
c701d5d9 | 761 | if (list_empty(&rnp->blkd_tasks)) { |
1217ed1b | 762 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
c701d5d9 | 763 | } else { |
12f5f524 | 764 | rnp->exp_tasks = rnp->blkd_tasks.next; |
1217ed1b | 765 | rcu_initiate_boost(rnp, flags); /* releases rnp->lock */ |
12f5f524 PM |
766 | must_wait = 1; |
767 | } | |
d9a3da06 | 768 | if (!must_wait) |
b40d293e | 769 | rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */ |
d9a3da06 PM |
770 | } |
771 | ||
236fefaf PM |
772 | /** |
773 | * synchronize_rcu_expedited - Brute-force RCU grace period | |
774 | * | |
775 | * Wait for an RCU-preempt grace period, but expedite it. The basic | |
776 | * idea is to invoke synchronize_sched_expedited() to push all the tasks to | |
777 | * the ->blkd_tasks lists and wait for this list to drain. This consumes | |
778 | * significant time on all CPUs and is unfriendly to real-time workloads, | |
779 | * so is thus not recommended for any sort of common-case code. | |
780 | * In fact, if you are using synchronize_rcu_expedited() in a loop, | |
781 | * please restructure your code to batch your updates, and then Use a | |
782 | * single synchronize_rcu() instead. | |
783 | * | |
784 | * Note that it is illegal to call this function while holding any lock | |
785 | * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal | |
786 | * to call this function from a CPU-hotplug notifier. Failing to observe | |
787 | * these restriction will result in deadlock. | |
019129d5 PM |
788 | */ |
789 | void synchronize_rcu_expedited(void) | |
790 | { | |
d9a3da06 PM |
791 | unsigned long flags; |
792 | struct rcu_node *rnp; | |
793 | struct rcu_state *rsp = &rcu_preempt_state; | |
794 | long snap; | |
795 | int trycount = 0; | |
796 | ||
797 | smp_mb(); /* Caller's modifications seen first by other CPUs. */ | |
798 | snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1; | |
799 | smp_mb(); /* Above access cannot bleed into critical section. */ | |
800 | ||
801 | /* | |
802 | * Acquire lock, falling back to synchronize_rcu() if too many | |
803 | * lock-acquisition failures. Of course, if someone does the | |
804 | * expedited grace period for us, just leave. | |
805 | */ | |
806 | while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) { | |
c701d5d9 | 807 | if (trycount++ < 10) { |
d9a3da06 | 808 | udelay(trycount * num_online_cpus()); |
c701d5d9 | 809 | } else { |
d9a3da06 PM |
810 | synchronize_rcu(); |
811 | return; | |
812 | } | |
813 | if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0) | |
814 | goto mb_ret; /* Others did our work for us. */ | |
815 | } | |
816 | if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0) | |
817 | goto unlock_mb_ret; /* Others did our work for us. */ | |
818 | ||
12f5f524 | 819 | /* force all RCU readers onto ->blkd_tasks lists. */ |
d9a3da06 PM |
820 | synchronize_sched_expedited(); |
821 | ||
1304afb2 | 822 | raw_spin_lock_irqsave(&rsp->onofflock, flags); |
d9a3da06 PM |
823 | |
824 | /* Initialize ->expmask for all non-leaf rcu_node structures. */ | |
825 | rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) { | |
1304afb2 | 826 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
d9a3da06 | 827 | rnp->expmask = rnp->qsmaskinit; |
1304afb2 | 828 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
d9a3da06 PM |
829 | } |
830 | ||
12f5f524 | 831 | /* Snapshot current state of ->blkd_tasks lists. */ |
d9a3da06 PM |
832 | rcu_for_each_leaf_node(rsp, rnp) |
833 | sync_rcu_preempt_exp_init(rsp, rnp); | |
834 | if (NUM_RCU_NODES > 1) | |
835 | sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp)); | |
836 | ||
1304afb2 | 837 | raw_spin_unlock_irqrestore(&rsp->onofflock, flags); |
d9a3da06 | 838 | |
12f5f524 | 839 | /* Wait for snapshotted ->blkd_tasks lists to drain. */ |
d9a3da06 PM |
840 | rnp = rcu_get_root(rsp); |
841 | wait_event(sync_rcu_preempt_exp_wq, | |
842 | sync_rcu_preempt_exp_done(rnp)); | |
843 | ||
844 | /* Clean up and exit. */ | |
845 | smp_mb(); /* ensure expedited GP seen before counter increment. */ | |
846 | ACCESS_ONCE(sync_rcu_preempt_exp_count)++; | |
847 | unlock_mb_ret: | |
848 | mutex_unlock(&sync_rcu_preempt_exp_mutex); | |
849 | mb_ret: | |
850 | smp_mb(); /* ensure subsequent action seen after grace period. */ | |
019129d5 PM |
851 | } |
852 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
853 | ||
e74f4c45 PM |
854 | /** |
855 | * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. | |
856 | */ | |
857 | void rcu_barrier(void) | |
858 | { | |
037b64ed | 859 | _rcu_barrier(&rcu_preempt_state); |
e74f4c45 PM |
860 | } |
861 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
862 | ||
1eba8f84 | 863 | /* |
6cc68793 | 864 | * Initialize preemptible RCU's state structures. |
1eba8f84 PM |
865 | */ |
866 | static void __init __rcu_init_preempt(void) | |
867 | { | |
394f99a9 | 868 | rcu_init_one(&rcu_preempt_state, &rcu_preempt_data); |
1eba8f84 PM |
869 | } |
870 | ||
f41d911f PM |
871 | #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ |
872 | ||
27f4d280 PM |
873 | static struct rcu_state *rcu_state = &rcu_sched_state; |
874 | ||
f41d911f PM |
875 | /* |
876 | * Tell them what RCU they are running. | |
877 | */ | |
0e0fc1c2 | 878 | static void __init rcu_bootup_announce(void) |
f41d911f PM |
879 | { |
880 | printk(KERN_INFO "Hierarchical RCU implementation.\n"); | |
26845c28 | 881 | rcu_bootup_announce_oddness(); |
f41d911f PM |
882 | } |
883 | ||
884 | /* | |
885 | * Return the number of RCU batches processed thus far for debug & stats. | |
886 | */ | |
887 | long rcu_batches_completed(void) | |
888 | { | |
889 | return rcu_batches_completed_sched(); | |
890 | } | |
891 | EXPORT_SYMBOL_GPL(rcu_batches_completed); | |
892 | ||
bf66f18e PM |
893 | /* |
894 | * Force a quiescent state for RCU, which, because there is no preemptible | |
895 | * RCU, becomes the same as rcu-sched. | |
896 | */ | |
897 | void rcu_force_quiescent_state(void) | |
898 | { | |
899 | rcu_sched_force_quiescent_state(); | |
900 | } | |
901 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); | |
902 | ||
cba6d0d6 PM |
903 | /* |
904 | * Because preemptible RCU does not exist, we never have to check for | |
905 | * CPUs being in quiescent states. | |
906 | */ | |
907 | static void rcu_preempt_note_context_switch(int cpu) | |
908 | { | |
909 | } | |
910 | ||
fc2219d4 | 911 | /* |
6cc68793 | 912 | * Because preemptible RCU does not exist, there are never any preempted |
fc2219d4 PM |
913 | * RCU readers. |
914 | */ | |
27f4d280 | 915 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 PM |
916 | { |
917 | return 0; | |
918 | } | |
919 | ||
b668c9cf PM |
920 | #ifdef CONFIG_HOTPLUG_CPU |
921 | ||
922 | /* Because preemptible RCU does not exist, no quieting of tasks. */ | |
d3f6bad3 | 923 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
b668c9cf | 924 | { |
1304afb2 | 925 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b668c9cf PM |
926 | } |
927 | ||
928 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
929 | ||
1ed509a2 | 930 | /* |
6cc68793 | 931 | * Because preemptible RCU does not exist, we never have to check for |
1ed509a2 PM |
932 | * tasks blocked within RCU read-side critical sections. |
933 | */ | |
934 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
935 | { | |
936 | } | |
937 | ||
f41d911f | 938 | /* |
6cc68793 | 939 | * Because preemptible RCU does not exist, we never have to check for |
f41d911f PM |
940 | * tasks blocked within RCU read-side critical sections. |
941 | */ | |
9bc8b558 | 942 | static int rcu_print_task_stall(struct rcu_node *rnp) |
f41d911f | 943 | { |
9bc8b558 | 944 | return 0; |
f41d911f PM |
945 | } |
946 | ||
b0e165c0 | 947 | /* |
6cc68793 | 948 | * Because there is no preemptible RCU, there can be no readers blocked, |
49e29126 PM |
949 | * so there is no need to check for blocked tasks. So check only for |
950 | * bogus qsmask values. | |
b0e165c0 PM |
951 | */ |
952 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
953 | { | |
49e29126 | 954 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
955 | } |
956 | ||
33f76148 PM |
957 | #ifdef CONFIG_HOTPLUG_CPU |
958 | ||
dd5d19ba | 959 | /* |
6cc68793 | 960 | * Because preemptible RCU does not exist, it never needs to migrate |
237c80c5 PM |
961 | * tasks that were blocked within RCU read-side critical sections, and |
962 | * such non-existent tasks cannot possibly have been blocking the current | |
963 | * grace period. | |
dd5d19ba | 964 | */ |
237c80c5 PM |
965 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
966 | struct rcu_node *rnp, | |
967 | struct rcu_data *rdp) | |
dd5d19ba | 968 | { |
237c80c5 | 969 | return 0; |
dd5d19ba PM |
970 | } |
971 | ||
e5601400 PM |
972 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
973 | ||
f41d911f | 974 | /* |
6cc68793 | 975 | * Because preemptible RCU does not exist, it never has any callbacks |
f41d911f PM |
976 | * to check. |
977 | */ | |
1eba8f84 | 978 | static void rcu_preempt_check_callbacks(int cpu) |
f41d911f PM |
979 | { |
980 | } | |
981 | ||
486e2593 PM |
982 | /* |
983 | * Queue an RCU callback for lazy invocation after a grace period. | |
984 | * This will likely be later named something like "call_rcu_lazy()", | |
985 | * but this change will require some way of tagging the lazy RCU | |
986 | * callbacks in the list of pending callbacks. Until then, this | |
987 | * function may only be called from __kfree_rcu(). | |
988 | * | |
989 | * Because there is no preemptible RCU, we use RCU-sched instead. | |
990 | */ | |
991 | void kfree_call_rcu(struct rcu_head *head, | |
992 | void (*func)(struct rcu_head *rcu)) | |
993 | { | |
994 | __call_rcu(head, func, &rcu_sched_state, 1); | |
995 | } | |
996 | EXPORT_SYMBOL_GPL(kfree_call_rcu); | |
997 | ||
019129d5 PM |
998 | /* |
999 | * Wait for an rcu-preempt grace period, but make it happen quickly. | |
6cc68793 | 1000 | * But because preemptible RCU does not exist, map to rcu-sched. |
019129d5 PM |
1001 | */ |
1002 | void synchronize_rcu_expedited(void) | |
1003 | { | |
1004 | synchronize_sched_expedited(); | |
1005 | } | |
1006 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
1007 | ||
d9a3da06 PM |
1008 | #ifdef CONFIG_HOTPLUG_CPU |
1009 | ||
1010 | /* | |
6cc68793 | 1011 | * Because preemptible RCU does not exist, there is never any need to |
d9a3da06 PM |
1012 | * report on tasks preempted in RCU read-side critical sections during |
1013 | * expedited RCU grace periods. | |
1014 | */ | |
b40d293e TG |
1015 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, |
1016 | bool wake) | |
d9a3da06 | 1017 | { |
d9a3da06 PM |
1018 | } |
1019 | ||
1020 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
1021 | ||
e74f4c45 | 1022 | /* |
6cc68793 | 1023 | * Because preemptible RCU does not exist, rcu_barrier() is just |
e74f4c45 PM |
1024 | * another name for rcu_barrier_sched(). |
1025 | */ | |
1026 | void rcu_barrier(void) | |
1027 | { | |
1028 | rcu_barrier_sched(); | |
1029 | } | |
1030 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
1031 | ||
1eba8f84 | 1032 | /* |
6cc68793 | 1033 | * Because preemptible RCU does not exist, it need not be initialized. |
1eba8f84 PM |
1034 | */ |
1035 | static void __init __rcu_init_preempt(void) | |
1036 | { | |
1037 | } | |
1038 | ||
f41d911f | 1039 | #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ |
8bd93a2c | 1040 | |
27f4d280 PM |
1041 | #ifdef CONFIG_RCU_BOOST |
1042 | ||
1043 | #include "rtmutex_common.h" | |
1044 | ||
0ea1f2eb PM |
1045 | #ifdef CONFIG_RCU_TRACE |
1046 | ||
1047 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) | |
1048 | { | |
1049 | if (list_empty(&rnp->blkd_tasks)) | |
1050 | rnp->n_balk_blkd_tasks++; | |
1051 | else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL) | |
1052 | rnp->n_balk_exp_gp_tasks++; | |
1053 | else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL) | |
1054 | rnp->n_balk_boost_tasks++; | |
1055 | else if (rnp->gp_tasks != NULL && rnp->qsmask != 0) | |
1056 | rnp->n_balk_notblocked++; | |
1057 | else if (rnp->gp_tasks != NULL && | |
a9f4793d | 1058 | ULONG_CMP_LT(jiffies, rnp->boost_time)) |
0ea1f2eb PM |
1059 | rnp->n_balk_notyet++; |
1060 | else | |
1061 | rnp->n_balk_nos++; | |
1062 | } | |
1063 | ||
1064 | #else /* #ifdef CONFIG_RCU_TRACE */ | |
1065 | ||
1066 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) | |
1067 | { | |
1068 | } | |
1069 | ||
1070 | #endif /* #else #ifdef CONFIG_RCU_TRACE */ | |
1071 | ||
27f4d280 PM |
1072 | /* |
1073 | * Carry out RCU priority boosting on the task indicated by ->exp_tasks | |
1074 | * or ->boost_tasks, advancing the pointer to the next task in the | |
1075 | * ->blkd_tasks list. | |
1076 | * | |
1077 | * Note that irqs must be enabled: boosting the task can block. | |
1078 | * Returns 1 if there are more tasks needing to be boosted. | |
1079 | */ | |
1080 | static int rcu_boost(struct rcu_node *rnp) | |
1081 | { | |
1082 | unsigned long flags; | |
1083 | struct rt_mutex mtx; | |
1084 | struct task_struct *t; | |
1085 | struct list_head *tb; | |
1086 | ||
1087 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) | |
1088 | return 0; /* Nothing left to boost. */ | |
1089 | ||
1090 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
1091 | ||
1092 | /* | |
1093 | * Recheck under the lock: all tasks in need of boosting | |
1094 | * might exit their RCU read-side critical sections on their own. | |
1095 | */ | |
1096 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { | |
1097 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
1098 | return 0; | |
1099 | } | |
1100 | ||
1101 | /* | |
1102 | * Preferentially boost tasks blocking expedited grace periods. | |
1103 | * This cannot starve the normal grace periods because a second | |
1104 | * expedited grace period must boost all blocked tasks, including | |
1105 | * those blocking the pre-existing normal grace period. | |
1106 | */ | |
0ea1f2eb | 1107 | if (rnp->exp_tasks != NULL) { |
27f4d280 | 1108 | tb = rnp->exp_tasks; |
0ea1f2eb PM |
1109 | rnp->n_exp_boosts++; |
1110 | } else { | |
27f4d280 | 1111 | tb = rnp->boost_tasks; |
0ea1f2eb PM |
1112 | rnp->n_normal_boosts++; |
1113 | } | |
1114 | rnp->n_tasks_boosted++; | |
27f4d280 PM |
1115 | |
1116 | /* | |
1117 | * We boost task t by manufacturing an rt_mutex that appears to | |
1118 | * be held by task t. We leave a pointer to that rt_mutex where | |
1119 | * task t can find it, and task t will release the mutex when it | |
1120 | * exits its outermost RCU read-side critical section. Then | |
1121 | * simply acquiring this artificial rt_mutex will boost task | |
1122 | * t's priority. (Thanks to tglx for suggesting this approach!) | |
1123 | * | |
1124 | * Note that task t must acquire rnp->lock to remove itself from | |
1125 | * the ->blkd_tasks list, which it will do from exit() if from | |
1126 | * nowhere else. We therefore are guaranteed that task t will | |
1127 | * stay around at least until we drop rnp->lock. Note that | |
1128 | * rnp->lock also resolves races between our priority boosting | |
1129 | * and task t's exiting its outermost RCU read-side critical | |
1130 | * section. | |
1131 | */ | |
1132 | t = container_of(tb, struct task_struct, rcu_node_entry); | |
1133 | rt_mutex_init_proxy_locked(&mtx, t); | |
1134 | t->rcu_boost_mutex = &mtx; | |
27f4d280 PM |
1135 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1136 | rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */ | |
1137 | rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ | |
1138 | ||
4f89b336 PM |
1139 | return ACCESS_ONCE(rnp->exp_tasks) != NULL || |
1140 | ACCESS_ONCE(rnp->boost_tasks) != NULL; | |
27f4d280 PM |
1141 | } |
1142 | ||
1143 | /* | |
1144 | * Timer handler to initiate waking up of boost kthreads that | |
1145 | * have yielded the CPU due to excessive numbers of tasks to | |
1146 | * boost. We wake up the per-rcu_node kthread, which in turn | |
1147 | * will wake up the booster kthread. | |
1148 | */ | |
1149 | static void rcu_boost_kthread_timer(unsigned long arg) | |
1150 | { | |
1217ed1b | 1151 | invoke_rcu_node_kthread((struct rcu_node *)arg); |
27f4d280 PM |
1152 | } |
1153 | ||
1154 | /* | |
1155 | * Priority-boosting kthread. One per leaf rcu_node and one for the | |
1156 | * root rcu_node. | |
1157 | */ | |
1158 | static int rcu_boost_kthread(void *arg) | |
1159 | { | |
1160 | struct rcu_node *rnp = (struct rcu_node *)arg; | |
1161 | int spincnt = 0; | |
1162 | int more2boost; | |
1163 | ||
385680a9 | 1164 | trace_rcu_utilization("Start boost kthread@init"); |
27f4d280 | 1165 | for (;;) { |
d71df90e | 1166 | rnp->boost_kthread_status = RCU_KTHREAD_WAITING; |
385680a9 | 1167 | trace_rcu_utilization("End boost kthread@rcu_wait"); |
08bca60a | 1168 | rcu_wait(rnp->boost_tasks || rnp->exp_tasks); |
385680a9 | 1169 | trace_rcu_utilization("Start boost kthread@rcu_wait"); |
d71df90e | 1170 | rnp->boost_kthread_status = RCU_KTHREAD_RUNNING; |
27f4d280 PM |
1171 | more2boost = rcu_boost(rnp); |
1172 | if (more2boost) | |
1173 | spincnt++; | |
1174 | else | |
1175 | spincnt = 0; | |
1176 | if (spincnt > 10) { | |
385680a9 | 1177 | trace_rcu_utilization("End boost kthread@rcu_yield"); |
27f4d280 | 1178 | rcu_yield(rcu_boost_kthread_timer, (unsigned long)rnp); |
385680a9 | 1179 | trace_rcu_utilization("Start boost kthread@rcu_yield"); |
27f4d280 PM |
1180 | spincnt = 0; |
1181 | } | |
1182 | } | |
1217ed1b | 1183 | /* NOTREACHED */ |
385680a9 | 1184 | trace_rcu_utilization("End boost kthread@notreached"); |
27f4d280 PM |
1185 | return 0; |
1186 | } | |
1187 | ||
1188 | /* | |
1189 | * Check to see if it is time to start boosting RCU readers that are | |
1190 | * blocking the current grace period, and, if so, tell the per-rcu_node | |
1191 | * kthread to start boosting them. If there is an expedited grace | |
1192 | * period in progress, it is always time to boost. | |
1193 | * | |
1217ed1b PM |
1194 | * The caller must hold rnp->lock, which this function releases, |
1195 | * but irqs remain disabled. The ->boost_kthread_task is immortal, | |
1196 | * so we don't need to worry about it going away. | |
27f4d280 | 1197 | */ |
1217ed1b | 1198 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
27f4d280 PM |
1199 | { |
1200 | struct task_struct *t; | |
1201 | ||
0ea1f2eb PM |
1202 | if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { |
1203 | rnp->n_balk_exp_gp_tasks++; | |
1217ed1b | 1204 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 | 1205 | return; |
0ea1f2eb | 1206 | } |
27f4d280 PM |
1207 | if (rnp->exp_tasks != NULL || |
1208 | (rnp->gp_tasks != NULL && | |
1209 | rnp->boost_tasks == NULL && | |
1210 | rnp->qsmask == 0 && | |
1211 | ULONG_CMP_GE(jiffies, rnp->boost_time))) { | |
1212 | if (rnp->exp_tasks == NULL) | |
1213 | rnp->boost_tasks = rnp->gp_tasks; | |
1217ed1b | 1214 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 PM |
1215 | t = rnp->boost_kthread_task; |
1216 | if (t != NULL) | |
1217 | wake_up_process(t); | |
1217ed1b | 1218 | } else { |
0ea1f2eb | 1219 | rcu_initiate_boost_trace(rnp); |
1217ed1b PM |
1220 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1221 | } | |
27f4d280 PM |
1222 | } |
1223 | ||
a46e0899 PM |
1224 | /* |
1225 | * Wake up the per-CPU kthread to invoke RCU callbacks. | |
1226 | */ | |
1227 | static void invoke_rcu_callbacks_kthread(void) | |
1228 | { | |
1229 | unsigned long flags; | |
1230 | ||
1231 | local_irq_save(flags); | |
1232 | __this_cpu_write(rcu_cpu_has_work, 1); | |
1eb52121 SL |
1233 | if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && |
1234 | current != __this_cpu_read(rcu_cpu_kthread_task)) | |
1235 | wake_up_process(__this_cpu_read(rcu_cpu_kthread_task)); | |
a46e0899 PM |
1236 | local_irq_restore(flags); |
1237 | } | |
1238 | ||
dff1672d PM |
1239 | /* |
1240 | * Is the current CPU running the RCU-callbacks kthread? | |
1241 | * Caller must have preemption disabled. | |
1242 | */ | |
1243 | static bool rcu_is_callbacks_kthread(void) | |
1244 | { | |
1245 | return __get_cpu_var(rcu_cpu_kthread_task) == current; | |
1246 | } | |
1247 | ||
0f962a5e PM |
1248 | /* |
1249 | * Set the affinity of the boost kthread. The CPU-hotplug locks are | |
1250 | * held, so no one should be messing with the existence of the boost | |
1251 | * kthread. | |
1252 | */ | |
27f4d280 PM |
1253 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, |
1254 | cpumask_var_t cm) | |
1255 | { | |
27f4d280 PM |
1256 | struct task_struct *t; |
1257 | ||
27f4d280 PM |
1258 | t = rnp->boost_kthread_task; |
1259 | if (t != NULL) | |
1260 | set_cpus_allowed_ptr(rnp->boost_kthread_task, cm); | |
27f4d280 PM |
1261 | } |
1262 | ||
1263 | #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) | |
1264 | ||
1265 | /* | |
1266 | * Do priority-boost accounting for the start of a new grace period. | |
1267 | */ | |
1268 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) | |
1269 | { | |
1270 | rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; | |
1271 | } | |
1272 | ||
27f4d280 PM |
1273 | /* |
1274 | * Create an RCU-boost kthread for the specified node if one does not | |
1275 | * already exist. We only create this kthread for preemptible RCU. | |
1276 | * Returns zero if all is well, a negated errno otherwise. | |
1277 | */ | |
1278 | static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, | |
1279 | struct rcu_node *rnp, | |
1280 | int rnp_index) | |
1281 | { | |
1282 | unsigned long flags; | |
1283 | struct sched_param sp; | |
1284 | struct task_struct *t; | |
1285 | ||
1286 | if (&rcu_preempt_state != rsp) | |
1287 | return 0; | |
a46e0899 | 1288 | rsp->boost = 1; |
27f4d280 PM |
1289 | if (rnp->boost_kthread_task != NULL) |
1290 | return 0; | |
1291 | t = kthread_create(rcu_boost_kthread, (void *)rnp, | |
5b61b0ba | 1292 | "rcub/%d", rnp_index); |
27f4d280 PM |
1293 | if (IS_ERR(t)) |
1294 | return PTR_ERR(t); | |
1295 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
1296 | rnp->boost_kthread_task = t; | |
1297 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
5b61b0ba | 1298 | sp.sched_priority = RCU_BOOST_PRIO; |
27f4d280 | 1299 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); |
9a432736 | 1300 | wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ |
27f4d280 PM |
1301 | return 0; |
1302 | } | |
1303 | ||
f8b7fc6b PM |
1304 | #ifdef CONFIG_HOTPLUG_CPU |
1305 | ||
1306 | /* | |
1307 | * Stop the RCU's per-CPU kthread when its CPU goes offline,. | |
1308 | */ | |
1309 | static void rcu_stop_cpu_kthread(int cpu) | |
1310 | { | |
1311 | struct task_struct *t; | |
1312 | ||
1313 | /* Stop the CPU's kthread. */ | |
1314 | t = per_cpu(rcu_cpu_kthread_task, cpu); | |
1315 | if (t != NULL) { | |
1316 | per_cpu(rcu_cpu_kthread_task, cpu) = NULL; | |
1317 | kthread_stop(t); | |
1318 | } | |
1319 | } | |
1320 | ||
1321 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
1322 | ||
1323 | static void rcu_kthread_do_work(void) | |
1324 | { | |
1325 | rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data)); | |
1326 | rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data)); | |
1327 | rcu_preempt_do_callbacks(); | |
1328 | } | |
1329 | ||
1330 | /* | |
1331 | * Wake up the specified per-rcu_node-structure kthread. | |
1332 | * Because the per-rcu_node kthreads are immortal, we don't need | |
1333 | * to do anything to keep them alive. | |
1334 | */ | |
1335 | static void invoke_rcu_node_kthread(struct rcu_node *rnp) | |
1336 | { | |
1337 | struct task_struct *t; | |
1338 | ||
1339 | t = rnp->node_kthread_task; | |
1340 | if (t != NULL) | |
1341 | wake_up_process(t); | |
1342 | } | |
1343 | ||
1344 | /* | |
1345 | * Set the specified CPU's kthread to run RT or not, as specified by | |
1346 | * the to_rt argument. The CPU-hotplug locks are held, so the task | |
1347 | * is not going away. | |
1348 | */ | |
1349 | static void rcu_cpu_kthread_setrt(int cpu, int to_rt) | |
1350 | { | |
1351 | int policy; | |
1352 | struct sched_param sp; | |
1353 | struct task_struct *t; | |
1354 | ||
1355 | t = per_cpu(rcu_cpu_kthread_task, cpu); | |
1356 | if (t == NULL) | |
1357 | return; | |
1358 | if (to_rt) { | |
1359 | policy = SCHED_FIFO; | |
1360 | sp.sched_priority = RCU_KTHREAD_PRIO; | |
1361 | } else { | |
1362 | policy = SCHED_NORMAL; | |
1363 | sp.sched_priority = 0; | |
1364 | } | |
1365 | sched_setscheduler_nocheck(t, policy, &sp); | |
1366 | } | |
1367 | ||
1368 | /* | |
1369 | * Timer handler to initiate the waking up of per-CPU kthreads that | |
1370 | * have yielded the CPU due to excess numbers of RCU callbacks. | |
1371 | * We wake up the per-rcu_node kthread, which in turn will wake up | |
1372 | * the booster kthread. | |
1373 | */ | |
1374 | static void rcu_cpu_kthread_timer(unsigned long arg) | |
1375 | { | |
1376 | struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg); | |
1377 | struct rcu_node *rnp = rdp->mynode; | |
1378 | ||
1379 | atomic_or(rdp->grpmask, &rnp->wakemask); | |
1380 | invoke_rcu_node_kthread(rnp); | |
1381 | } | |
1382 | ||
1383 | /* | |
1384 | * Drop to non-real-time priority and yield, but only after posting a | |
1385 | * timer that will cause us to regain our real-time priority if we | |
1386 | * remain preempted. Either way, we restore our real-time priority | |
1387 | * before returning. | |
1388 | */ | |
1389 | static void rcu_yield(void (*f)(unsigned long), unsigned long arg) | |
1390 | { | |
1391 | struct sched_param sp; | |
1392 | struct timer_list yield_timer; | |
5b61b0ba | 1393 | int prio = current->rt_priority; |
f8b7fc6b PM |
1394 | |
1395 | setup_timer_on_stack(&yield_timer, f, arg); | |
1396 | mod_timer(&yield_timer, jiffies + 2); | |
1397 | sp.sched_priority = 0; | |
1398 | sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp); | |
1399 | set_user_nice(current, 19); | |
1400 | schedule(); | |
5b61b0ba MG |
1401 | set_user_nice(current, 0); |
1402 | sp.sched_priority = prio; | |
f8b7fc6b PM |
1403 | sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); |
1404 | del_timer(&yield_timer); | |
1405 | } | |
1406 | ||
1407 | /* | |
1408 | * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU. | |
1409 | * This can happen while the corresponding CPU is either coming online | |
1410 | * or going offline. We cannot wait until the CPU is fully online | |
1411 | * before starting the kthread, because the various notifier functions | |
1412 | * can wait for RCU grace periods. So we park rcu_cpu_kthread() until | |
1413 | * the corresponding CPU is online. | |
1414 | * | |
1415 | * Return 1 if the kthread needs to stop, 0 otherwise. | |
1416 | * | |
1417 | * Caller must disable bh. This function can momentarily enable it. | |
1418 | */ | |
1419 | static int rcu_cpu_kthread_should_stop(int cpu) | |
1420 | { | |
1421 | while (cpu_is_offline(cpu) || | |
1422 | !cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu)) || | |
1423 | smp_processor_id() != cpu) { | |
1424 | if (kthread_should_stop()) | |
1425 | return 1; | |
1426 | per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; | |
1427 | per_cpu(rcu_cpu_kthread_cpu, cpu) = raw_smp_processor_id(); | |
1428 | local_bh_enable(); | |
1429 | schedule_timeout_uninterruptible(1); | |
1430 | if (!cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu))) | |
1431 | set_cpus_allowed_ptr(current, cpumask_of(cpu)); | |
1432 | local_bh_disable(); | |
1433 | } | |
1434 | per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu; | |
1435 | return 0; | |
1436 | } | |
1437 | ||
1438 | /* | |
1439 | * Per-CPU kernel thread that invokes RCU callbacks. This replaces the | |
e0f23060 PM |
1440 | * RCU softirq used in flavors and configurations of RCU that do not |
1441 | * support RCU priority boosting. | |
f8b7fc6b PM |
1442 | */ |
1443 | static int rcu_cpu_kthread(void *arg) | |
1444 | { | |
1445 | int cpu = (int)(long)arg; | |
1446 | unsigned long flags; | |
1447 | int spincnt = 0; | |
1448 | unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu); | |
1449 | char work; | |
1450 | char *workp = &per_cpu(rcu_cpu_has_work, cpu); | |
1451 | ||
385680a9 | 1452 | trace_rcu_utilization("Start CPU kthread@init"); |
f8b7fc6b PM |
1453 | for (;;) { |
1454 | *statusp = RCU_KTHREAD_WAITING; | |
385680a9 | 1455 | trace_rcu_utilization("End CPU kthread@rcu_wait"); |
f8b7fc6b | 1456 | rcu_wait(*workp != 0 || kthread_should_stop()); |
385680a9 | 1457 | trace_rcu_utilization("Start CPU kthread@rcu_wait"); |
f8b7fc6b PM |
1458 | local_bh_disable(); |
1459 | if (rcu_cpu_kthread_should_stop(cpu)) { | |
1460 | local_bh_enable(); | |
1461 | break; | |
1462 | } | |
1463 | *statusp = RCU_KTHREAD_RUNNING; | |
1464 | per_cpu(rcu_cpu_kthread_loops, cpu)++; | |
1465 | local_irq_save(flags); | |
1466 | work = *workp; | |
1467 | *workp = 0; | |
1468 | local_irq_restore(flags); | |
1469 | if (work) | |
1470 | rcu_kthread_do_work(); | |
1471 | local_bh_enable(); | |
1472 | if (*workp != 0) | |
1473 | spincnt++; | |
1474 | else | |
1475 | spincnt = 0; | |
1476 | if (spincnt > 10) { | |
1477 | *statusp = RCU_KTHREAD_YIELDING; | |
385680a9 | 1478 | trace_rcu_utilization("End CPU kthread@rcu_yield"); |
f8b7fc6b | 1479 | rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu); |
385680a9 | 1480 | trace_rcu_utilization("Start CPU kthread@rcu_yield"); |
f8b7fc6b PM |
1481 | spincnt = 0; |
1482 | } | |
1483 | } | |
1484 | *statusp = RCU_KTHREAD_STOPPED; | |
385680a9 | 1485 | trace_rcu_utilization("End CPU kthread@term"); |
f8b7fc6b PM |
1486 | return 0; |
1487 | } | |
1488 | ||
1489 | /* | |
1490 | * Spawn a per-CPU kthread, setting up affinity and priority. | |
1491 | * Because the CPU hotplug lock is held, no other CPU will be attempting | |
1492 | * to manipulate rcu_cpu_kthread_task. There might be another CPU | |
1493 | * attempting to access it during boot, but the locking in kthread_bind() | |
1494 | * will enforce sufficient ordering. | |
1495 | * | |
1496 | * Please note that we cannot simply refuse to wake up the per-CPU | |
1497 | * kthread because kthreads are created in TASK_UNINTERRUPTIBLE state, | |
1498 | * which can result in softlockup complaints if the task ends up being | |
1499 | * idle for more than a couple of minutes. | |
1500 | * | |
1501 | * However, please note also that we cannot bind the per-CPU kthread to its | |
1502 | * CPU until that CPU is fully online. We also cannot wait until the | |
1503 | * CPU is fully online before we create its per-CPU kthread, as this would | |
1504 | * deadlock the system when CPU notifiers tried waiting for grace | |
1505 | * periods. So we bind the per-CPU kthread to its CPU only if the CPU | |
1506 | * is online. If its CPU is not yet fully online, then the code in | |
1507 | * rcu_cpu_kthread() will wait until it is fully online, and then do | |
1508 | * the binding. | |
1509 | */ | |
1510 | static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu) | |
1511 | { | |
1512 | struct sched_param sp; | |
1513 | struct task_struct *t; | |
1514 | ||
b0d30417 | 1515 | if (!rcu_scheduler_fully_active || |
f8b7fc6b PM |
1516 | per_cpu(rcu_cpu_kthread_task, cpu) != NULL) |
1517 | return 0; | |
1f288094 ED |
1518 | t = kthread_create_on_node(rcu_cpu_kthread, |
1519 | (void *)(long)cpu, | |
1520 | cpu_to_node(cpu), | |
5b61b0ba | 1521 | "rcuc/%d", cpu); |
f8b7fc6b PM |
1522 | if (IS_ERR(t)) |
1523 | return PTR_ERR(t); | |
1524 | if (cpu_online(cpu)) | |
1525 | kthread_bind(t, cpu); | |
1526 | per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu; | |
1527 | WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL); | |
1528 | sp.sched_priority = RCU_KTHREAD_PRIO; | |
1529 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); | |
1530 | per_cpu(rcu_cpu_kthread_task, cpu) = t; | |
1531 | wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */ | |
1532 | return 0; | |
1533 | } | |
1534 | ||
1535 | /* | |
1536 | * Per-rcu_node kthread, which is in charge of waking up the per-CPU | |
1537 | * kthreads when needed. We ignore requests to wake up kthreads | |
1538 | * for offline CPUs, which is OK because force_quiescent_state() | |
1539 | * takes care of this case. | |
1540 | */ | |
1541 | static int rcu_node_kthread(void *arg) | |
1542 | { | |
1543 | int cpu; | |
1544 | unsigned long flags; | |
1545 | unsigned long mask; | |
1546 | struct rcu_node *rnp = (struct rcu_node *)arg; | |
1547 | struct sched_param sp; | |
1548 | struct task_struct *t; | |
1549 | ||
1550 | for (;;) { | |
1551 | rnp->node_kthread_status = RCU_KTHREAD_WAITING; | |
1552 | rcu_wait(atomic_read(&rnp->wakemask) != 0); | |
1553 | rnp->node_kthread_status = RCU_KTHREAD_RUNNING; | |
1554 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
1555 | mask = atomic_xchg(&rnp->wakemask, 0); | |
1556 | rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */ | |
1557 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) { | |
1558 | if ((mask & 0x1) == 0) | |
1559 | continue; | |
1560 | preempt_disable(); | |
1561 | t = per_cpu(rcu_cpu_kthread_task, cpu); | |
1562 | if (!cpu_online(cpu) || t == NULL) { | |
1563 | preempt_enable(); | |
1564 | continue; | |
1565 | } | |
1566 | per_cpu(rcu_cpu_has_work, cpu) = 1; | |
1567 | sp.sched_priority = RCU_KTHREAD_PRIO; | |
1568 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); | |
1569 | preempt_enable(); | |
1570 | } | |
1571 | } | |
1572 | /* NOTREACHED */ | |
1573 | rnp->node_kthread_status = RCU_KTHREAD_STOPPED; | |
1574 | return 0; | |
1575 | } | |
1576 | ||
1577 | /* | |
1578 | * Set the per-rcu_node kthread's affinity to cover all CPUs that are | |
1579 | * served by the rcu_node in question. The CPU hotplug lock is still | |
1580 | * held, so the value of rnp->qsmaskinit will be stable. | |
1581 | * | |
1582 | * We don't include outgoingcpu in the affinity set, use -1 if there is | |
1583 | * no outgoing CPU. If there are no CPUs left in the affinity set, | |
1584 | * this function allows the kthread to execute on any CPU. | |
1585 | */ | |
1586 | static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) | |
1587 | { | |
1588 | cpumask_var_t cm; | |
1589 | int cpu; | |
1590 | unsigned long mask = rnp->qsmaskinit; | |
1591 | ||
1592 | if (rnp->node_kthread_task == NULL) | |
1593 | return; | |
1594 | if (!alloc_cpumask_var(&cm, GFP_KERNEL)) | |
1595 | return; | |
1596 | cpumask_clear(cm); | |
1597 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) | |
1598 | if ((mask & 0x1) && cpu != outgoingcpu) | |
1599 | cpumask_set_cpu(cpu, cm); | |
1600 | if (cpumask_weight(cm) == 0) { | |
1601 | cpumask_setall(cm); | |
1602 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) | |
1603 | cpumask_clear_cpu(cpu, cm); | |
1604 | WARN_ON_ONCE(cpumask_weight(cm) == 0); | |
1605 | } | |
1606 | set_cpus_allowed_ptr(rnp->node_kthread_task, cm); | |
1607 | rcu_boost_kthread_setaffinity(rnp, cm); | |
1608 | free_cpumask_var(cm); | |
1609 | } | |
1610 | ||
1611 | /* | |
1612 | * Spawn a per-rcu_node kthread, setting priority and affinity. | |
1613 | * Called during boot before online/offline can happen, or, if | |
1614 | * during runtime, with the main CPU-hotplug locks held. So only | |
1615 | * one of these can be executing at a time. | |
1616 | */ | |
1617 | static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp, | |
1618 | struct rcu_node *rnp) | |
1619 | { | |
1620 | unsigned long flags; | |
1621 | int rnp_index = rnp - &rsp->node[0]; | |
1622 | struct sched_param sp; | |
1623 | struct task_struct *t; | |
1624 | ||
b0d30417 | 1625 | if (!rcu_scheduler_fully_active || |
f8b7fc6b PM |
1626 | rnp->qsmaskinit == 0) |
1627 | return 0; | |
1628 | if (rnp->node_kthread_task == NULL) { | |
1629 | t = kthread_create(rcu_node_kthread, (void *)rnp, | |
5b61b0ba | 1630 | "rcun/%d", rnp_index); |
f8b7fc6b PM |
1631 | if (IS_ERR(t)) |
1632 | return PTR_ERR(t); | |
1633 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
1634 | rnp->node_kthread_task = t; | |
1635 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
1636 | sp.sched_priority = 99; | |
1637 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); | |
1638 | wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ | |
1639 | } | |
1640 | return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index); | |
1641 | } | |
1642 | ||
1643 | /* | |
1644 | * Spawn all kthreads -- called as soon as the scheduler is running. | |
1645 | */ | |
1646 | static int __init rcu_spawn_kthreads(void) | |
1647 | { | |
1648 | int cpu; | |
1649 | struct rcu_node *rnp; | |
1650 | ||
b0d30417 | 1651 | rcu_scheduler_fully_active = 1; |
f8b7fc6b PM |
1652 | for_each_possible_cpu(cpu) { |
1653 | per_cpu(rcu_cpu_has_work, cpu) = 0; | |
1654 | if (cpu_online(cpu)) | |
1655 | (void)rcu_spawn_one_cpu_kthread(cpu); | |
1656 | } | |
1657 | rnp = rcu_get_root(rcu_state); | |
1658 | (void)rcu_spawn_one_node_kthread(rcu_state, rnp); | |
1659 | if (NUM_RCU_NODES > 1) { | |
1660 | rcu_for_each_leaf_node(rcu_state, rnp) | |
1661 | (void)rcu_spawn_one_node_kthread(rcu_state, rnp); | |
1662 | } | |
1663 | return 0; | |
1664 | } | |
1665 | early_initcall(rcu_spawn_kthreads); | |
1666 | ||
1667 | static void __cpuinit rcu_prepare_kthreads(int cpu) | |
1668 | { | |
1669 | struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu); | |
1670 | struct rcu_node *rnp = rdp->mynode; | |
1671 | ||
1672 | /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ | |
b0d30417 | 1673 | if (rcu_scheduler_fully_active) { |
f8b7fc6b PM |
1674 | (void)rcu_spawn_one_cpu_kthread(cpu); |
1675 | if (rnp->node_kthread_task == NULL) | |
1676 | (void)rcu_spawn_one_node_kthread(rcu_state, rnp); | |
1677 | } | |
1678 | } | |
1679 | ||
27f4d280 PM |
1680 | #else /* #ifdef CONFIG_RCU_BOOST */ |
1681 | ||
1217ed1b | 1682 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
27f4d280 | 1683 | { |
1217ed1b | 1684 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 PM |
1685 | } |
1686 | ||
a46e0899 | 1687 | static void invoke_rcu_callbacks_kthread(void) |
27f4d280 | 1688 | { |
a46e0899 | 1689 | WARN_ON_ONCE(1); |
27f4d280 PM |
1690 | } |
1691 | ||
dff1672d PM |
1692 | static bool rcu_is_callbacks_kthread(void) |
1693 | { | |
1694 | return false; | |
1695 | } | |
1696 | ||
27f4d280 PM |
1697 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) |
1698 | { | |
1699 | } | |
1700 | ||
f8b7fc6b PM |
1701 | #ifdef CONFIG_HOTPLUG_CPU |
1702 | ||
1703 | static void rcu_stop_cpu_kthread(int cpu) | |
1704 | { | |
1705 | } | |
1706 | ||
1707 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
1708 | ||
1709 | static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) | |
1710 | { | |
1711 | } | |
1712 | ||
1713 | static void rcu_cpu_kthread_setrt(int cpu, int to_rt) | |
1714 | { | |
1715 | } | |
1716 | ||
b0d30417 PM |
1717 | static int __init rcu_scheduler_really_started(void) |
1718 | { | |
1719 | rcu_scheduler_fully_active = 1; | |
1720 | return 0; | |
1721 | } | |
1722 | early_initcall(rcu_scheduler_really_started); | |
1723 | ||
f8b7fc6b PM |
1724 | static void __cpuinit rcu_prepare_kthreads(int cpu) |
1725 | { | |
1726 | } | |
1727 | ||
27f4d280 PM |
1728 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
1729 | ||
8bd93a2c PM |
1730 | #if !defined(CONFIG_RCU_FAST_NO_HZ) |
1731 | ||
1732 | /* | |
1733 | * Check to see if any future RCU-related work will need to be done | |
1734 | * by the current CPU, even if none need be done immediately, returning | |
1735 | * 1 if so. This function is part of the RCU implementation; it is -not- | |
1736 | * an exported member of the RCU API. | |
1737 | * | |
7cb92499 PM |
1738 | * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs |
1739 | * any flavor of RCU. | |
8bd93a2c | 1740 | */ |
aa9b1630 | 1741 | int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) |
8bd93a2c | 1742 | { |
aa9b1630 | 1743 | *delta_jiffies = ULONG_MAX; |
aea1b35e PM |
1744 | return rcu_cpu_has_callbacks(cpu); |
1745 | } | |
1746 | ||
7cb92499 PM |
1747 | /* |
1748 | * Because we do not have RCU_FAST_NO_HZ, don't bother initializing for it. | |
1749 | */ | |
1750 | static void rcu_prepare_for_idle_init(int cpu) | |
1751 | { | |
1752 | } | |
1753 | ||
1754 | /* | |
1755 | * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up | |
1756 | * after it. | |
1757 | */ | |
1758 | static void rcu_cleanup_after_idle(int cpu) | |
1759 | { | |
1760 | } | |
1761 | ||
aea1b35e | 1762 | /* |
a858af28 | 1763 | * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n, |
aea1b35e PM |
1764 | * is nothing. |
1765 | */ | |
1766 | static void rcu_prepare_for_idle(int cpu) | |
1767 | { | |
1768 | } | |
1769 | ||
c57afe80 PM |
1770 | /* |
1771 | * Don't bother keeping a running count of the number of RCU callbacks | |
1772 | * posted because CONFIG_RCU_FAST_NO_HZ=n. | |
1773 | */ | |
1774 | static void rcu_idle_count_callbacks_posted(void) | |
1775 | { | |
1776 | } | |
1777 | ||
8bd93a2c PM |
1778 | #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
1779 | ||
f23f7fa1 PM |
1780 | /* |
1781 | * This code is invoked when a CPU goes idle, at which point we want | |
1782 | * to have the CPU do everything required for RCU so that it can enter | |
1783 | * the energy-efficient dyntick-idle mode. This is handled by a | |
1784 | * state machine implemented by rcu_prepare_for_idle() below. | |
1785 | * | |
1786 | * The following three proprocessor symbols control this state machine: | |
1787 | * | |
1788 | * RCU_IDLE_FLUSHES gives the maximum number of times that we will attempt | |
1789 | * to satisfy RCU. Beyond this point, it is better to incur a periodic | |
1790 | * scheduling-clock interrupt than to loop through the state machine | |
1791 | * at full power. | |
1792 | * RCU_IDLE_OPT_FLUSHES gives the number of RCU_IDLE_FLUSHES that are | |
1793 | * optional if RCU does not need anything immediately from this | |
1794 | * CPU, even if this CPU still has RCU callbacks queued. The first | |
1795 | * times through the state machine are mandatory: we need to give | |
1796 | * the state machine a chance to communicate a quiescent state | |
1797 | * to the RCU core. | |
1798 | * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted | |
1799 | * to sleep in dyntick-idle mode with RCU callbacks pending. This | |
1800 | * is sized to be roughly one RCU grace period. Those energy-efficiency | |
1801 | * benchmarkers who might otherwise be tempted to set this to a large | |
1802 | * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your | |
1803 | * system. And if you are -that- concerned about energy efficiency, | |
1804 | * just power the system down and be done with it! | |
778d250a PM |
1805 | * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is |
1806 | * permitted to sleep in dyntick-idle mode with only lazy RCU | |
1807 | * callbacks pending. Setting this too high can OOM your system. | |
f23f7fa1 PM |
1808 | * |
1809 | * The values below work well in practice. If future workloads require | |
1810 | * adjustment, they can be converted into kernel config parameters, though | |
1811 | * making the state machine smarter might be a better option. | |
1812 | */ | |
1813 | #define RCU_IDLE_FLUSHES 5 /* Number of dyntick-idle tries. */ | |
1814 | #define RCU_IDLE_OPT_FLUSHES 3 /* Optional dyntick-idle tries. */ | |
e84c48ae | 1815 | #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */ |
778d250a | 1816 | #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ |
f23f7fa1 | 1817 | |
9d2ad243 PM |
1818 | extern int tick_nohz_enabled; |
1819 | ||
486e2593 PM |
1820 | /* |
1821 | * Does the specified flavor of RCU have non-lazy callbacks pending on | |
1822 | * the specified CPU? Both RCU flavor and CPU are specified by the | |
1823 | * rcu_data structure. | |
1824 | */ | |
1825 | static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp) | |
1826 | { | |
1827 | return rdp->qlen != rdp->qlen_lazy; | |
1828 | } | |
1829 | ||
1830 | #ifdef CONFIG_TREE_PREEMPT_RCU | |
1831 | ||
1832 | /* | |
1833 | * Are there non-lazy RCU-preempt callbacks? (There cannot be if there | |
1834 | * is no RCU-preempt in the kernel.) | |
1835 | */ | |
1836 | static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu) | |
1837 | { | |
1838 | struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); | |
1839 | ||
1840 | return __rcu_cpu_has_nonlazy_callbacks(rdp); | |
1841 | } | |
1842 | ||
1843 | #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ | |
1844 | ||
1845 | static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu) | |
1846 | { | |
1847 | return 0; | |
1848 | } | |
1849 | ||
1850 | #endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */ | |
1851 | ||
1852 | /* | |
1853 | * Does any flavor of RCU have non-lazy callbacks on the specified CPU? | |
1854 | */ | |
1855 | static bool rcu_cpu_has_nonlazy_callbacks(int cpu) | |
1856 | { | |
1857 | return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) || | |
1858 | __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) || | |
1859 | rcu_preempt_cpu_has_nonlazy_callbacks(cpu); | |
1860 | } | |
1861 | ||
aa9b1630 PM |
1862 | /* |
1863 | * Allow the CPU to enter dyntick-idle mode if either: (1) There are no | |
1864 | * callbacks on this CPU, (2) this CPU has not yet attempted to enter | |
1865 | * dyntick-idle mode, or (3) this CPU is in the process of attempting to | |
1866 | * enter dyntick-idle mode. Otherwise, if we have recently tried and failed | |
1867 | * to enter dyntick-idle mode, we refuse to try to enter it. After all, | |
1868 | * it is better to incur scheduling-clock interrupts than to spin | |
1869 | * continuously for the same time duration! | |
1870 | * | |
1871 | * The delta_jiffies argument is used to store the time when RCU is | |
1872 | * going to need the CPU again if it still has callbacks. The reason | |
1873 | * for this is that rcu_prepare_for_idle() might need to post a timer, | |
1874 | * but if so, it will do so after tick_nohz_stop_sched_tick() has set | |
1875 | * the wakeup time for this CPU. This means that RCU's timer can be | |
1876 | * delayed until the wakeup time, which defeats the purpose of posting | |
1877 | * a timer. | |
1878 | */ | |
1879 | int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) | |
1880 | { | |
1881 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); | |
1882 | ||
1883 | /* Flag a new idle sojourn to the idle-entry state machine. */ | |
1884 | rdtp->idle_first_pass = 1; | |
1885 | /* If no callbacks, RCU doesn't need the CPU. */ | |
1886 | if (!rcu_cpu_has_callbacks(cpu)) { | |
1887 | *delta_jiffies = ULONG_MAX; | |
1888 | return 0; | |
1889 | } | |
1890 | if (rdtp->dyntick_holdoff == jiffies) { | |
1891 | /* RCU recently tried and failed, so don't try again. */ | |
1892 | *delta_jiffies = 1; | |
1893 | return 1; | |
1894 | } | |
1895 | /* Set up for the possibility that RCU will post a timer. */ | |
e84c48ae PM |
1896 | if (rcu_cpu_has_nonlazy_callbacks(cpu)) { |
1897 | *delta_jiffies = round_up(RCU_IDLE_GP_DELAY + jiffies, | |
1898 | RCU_IDLE_GP_DELAY) - jiffies; | |
1899 | } else { | |
1900 | *delta_jiffies = jiffies + RCU_IDLE_LAZY_GP_DELAY; | |
1901 | *delta_jiffies = round_jiffies(*delta_jiffies) - jiffies; | |
1902 | } | |
aa9b1630 PM |
1903 | return 0; |
1904 | } | |
1905 | ||
21e52e15 PM |
1906 | /* |
1907 | * Handler for smp_call_function_single(). The only point of this | |
1908 | * handler is to wake the CPU up, so the handler does only tracing. | |
1909 | */ | |
1910 | void rcu_idle_demigrate(void *unused) | |
1911 | { | |
1912 | trace_rcu_prep_idle("Demigrate"); | |
1913 | } | |
1914 | ||
7cb92499 PM |
1915 | /* |
1916 | * Timer handler used to force CPU to start pushing its remaining RCU | |
1917 | * callbacks in the case where it entered dyntick-idle mode with callbacks | |
1918 | * pending. The hander doesn't really need to do anything because the | |
1919 | * real work is done upon re-entry to idle, or by the next scheduling-clock | |
1920 | * interrupt should idle not be re-entered. | |
21e52e15 PM |
1921 | * |
1922 | * One special case: the timer gets migrated without awakening the CPU | |
1923 | * on which the timer was scheduled on. In this case, we must wake up | |
1924 | * that CPU. We do so with smp_call_function_single(). | |
7cb92499 | 1925 | */ |
21e52e15 | 1926 | static void rcu_idle_gp_timer_func(unsigned long cpu_in) |
7cb92499 | 1927 | { |
21e52e15 PM |
1928 | int cpu = (int)cpu_in; |
1929 | ||
7cb92499 | 1930 | trace_rcu_prep_idle("Timer"); |
21e52e15 PM |
1931 | if (cpu != smp_processor_id()) |
1932 | smp_call_function_single(cpu, rcu_idle_demigrate, NULL, 0); | |
1933 | else | |
1934 | WARN_ON_ONCE(1); /* Getting here can hang the system... */ | |
7cb92499 PM |
1935 | } |
1936 | ||
1937 | /* | |
1938 | * Initialize the timer used to pull CPUs out of dyntick-idle mode. | |
1939 | */ | |
1940 | static void rcu_prepare_for_idle_init(int cpu) | |
1941 | { | |
5955f7ee PM |
1942 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
1943 | ||
1944 | rdtp->dyntick_holdoff = jiffies - 1; | |
1945 | setup_timer(&rdtp->idle_gp_timer, rcu_idle_gp_timer_func, cpu); | |
1946 | rdtp->idle_gp_timer_expires = jiffies - 1; | |
1947 | rdtp->idle_first_pass = 1; | |
7cb92499 PM |
1948 | } |
1949 | ||
1950 | /* | |
1951 | * Clean up for exit from idle. Because we are exiting from idle, there | |
5955f7ee | 1952 | * is no longer any point to ->idle_gp_timer, so cancel it. This will |
7cb92499 PM |
1953 | * do nothing if this timer is not active, so just cancel it unconditionally. |
1954 | */ | |
1955 | static void rcu_cleanup_after_idle(int cpu) | |
1956 | { | |
5955f7ee PM |
1957 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
1958 | ||
1959 | del_timer(&rdtp->idle_gp_timer); | |
2fdbb31b | 1960 | trace_rcu_prep_idle("Cleanup after idle"); |
9d2ad243 | 1961 | rdtp->tick_nohz_enabled_snap = ACCESS_ONCE(tick_nohz_enabled); |
7cb92499 PM |
1962 | } |
1963 | ||
aea1b35e PM |
1964 | /* |
1965 | * Check to see if any RCU-related work can be done by the current CPU, | |
1966 | * and if so, schedule a softirq to get it done. This function is part | |
1967 | * of the RCU implementation; it is -not- an exported member of the RCU API. | |
8bd93a2c | 1968 | * |
aea1b35e PM |
1969 | * The idea is for the current CPU to clear out all work required by the |
1970 | * RCU core for the current grace period, so that this CPU can be permitted | |
1971 | * to enter dyntick-idle mode. In some cases, it will need to be awakened | |
1972 | * at the end of the grace period by whatever CPU ends the grace period. | |
1973 | * This allows CPUs to go dyntick-idle more quickly, and to reduce the | |
1974 | * number of wakeups by a modest integer factor. | |
a47cd880 PM |
1975 | * |
1976 | * Because it is not legal to invoke rcu_process_callbacks() with irqs | |
1977 | * disabled, we do one pass of force_quiescent_state(), then do a | |
a46e0899 | 1978 | * invoke_rcu_core() to cause rcu_process_callbacks() to be invoked |
5955f7ee | 1979 | * later. The ->dyntick_drain field controls the sequencing. |
aea1b35e PM |
1980 | * |
1981 | * The caller must have disabled interrupts. | |
8bd93a2c | 1982 | */ |
aea1b35e | 1983 | static void rcu_prepare_for_idle(int cpu) |
8bd93a2c | 1984 | { |
f511fc62 | 1985 | struct timer_list *tp; |
5955f7ee | 1986 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
9d2ad243 PM |
1987 | int tne; |
1988 | ||
1989 | /* Handle nohz enablement switches conservatively. */ | |
1990 | tne = ACCESS_ONCE(tick_nohz_enabled); | |
1991 | if (tne != rdtp->tick_nohz_enabled_snap) { | |
1992 | if (rcu_cpu_has_callbacks(cpu)) | |
1993 | invoke_rcu_core(); /* force nohz to see update. */ | |
1994 | rdtp->tick_nohz_enabled_snap = tne; | |
1995 | return; | |
1996 | } | |
1997 | if (!tne) | |
1998 | return; | |
f511fc62 | 1999 | |
c57afe80 PM |
2000 | /* |
2001 | * If this is an idle re-entry, for example, due to use of | |
2002 | * RCU_NONIDLE() or the new idle-loop tracing API within the idle | |
2003 | * loop, then don't take any state-machine actions, unless the | |
2004 | * momentary exit from idle queued additional non-lazy callbacks. | |
5955f7ee | 2005 | * Instead, repost the ->idle_gp_timer if this CPU has callbacks |
c57afe80 PM |
2006 | * pending. |
2007 | */ | |
5955f7ee PM |
2008 | if (!rdtp->idle_first_pass && |
2009 | (rdtp->nonlazy_posted == rdtp->nonlazy_posted_snap)) { | |
f511fc62 | 2010 | if (rcu_cpu_has_callbacks(cpu)) { |
5955f7ee PM |
2011 | tp = &rdtp->idle_gp_timer; |
2012 | mod_timer_pinned(tp, rdtp->idle_gp_timer_expires); | |
f511fc62 | 2013 | } |
c57afe80 PM |
2014 | return; |
2015 | } | |
5955f7ee PM |
2016 | rdtp->idle_first_pass = 0; |
2017 | rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted - 1; | |
c57afe80 | 2018 | |
3084f2f8 | 2019 | /* |
f535a607 PM |
2020 | * If there are no callbacks on this CPU, enter dyntick-idle mode. |
2021 | * Also reset state to avoid prejudicing later attempts. | |
3084f2f8 | 2022 | */ |
aea1b35e | 2023 | if (!rcu_cpu_has_callbacks(cpu)) { |
5955f7ee PM |
2024 | rdtp->dyntick_holdoff = jiffies - 1; |
2025 | rdtp->dyntick_drain = 0; | |
433cdddc | 2026 | trace_rcu_prep_idle("No callbacks"); |
aea1b35e | 2027 | return; |
77e38ed3 | 2028 | } |
3084f2f8 PM |
2029 | |
2030 | /* | |
2031 | * If in holdoff mode, just return. We will presumably have | |
2032 | * refrained from disabling the scheduling-clock tick. | |
2033 | */ | |
5955f7ee | 2034 | if (rdtp->dyntick_holdoff == jiffies) { |
433cdddc | 2035 | trace_rcu_prep_idle("In holdoff"); |
aea1b35e | 2036 | return; |
433cdddc | 2037 | } |
a47cd880 | 2038 | |
5955f7ee PM |
2039 | /* Check and update the ->dyntick_drain sequencing. */ |
2040 | if (rdtp->dyntick_drain <= 0) { | |
a47cd880 | 2041 | /* First time through, initialize the counter. */ |
5955f7ee PM |
2042 | rdtp->dyntick_drain = RCU_IDLE_FLUSHES; |
2043 | } else if (rdtp->dyntick_drain <= RCU_IDLE_OPT_FLUSHES && | |
c3ce910b PM |
2044 | !rcu_pending(cpu) && |
2045 | !local_softirq_pending()) { | |
7cb92499 | 2046 | /* Can we go dyntick-idle despite still having callbacks? */ |
5955f7ee PM |
2047 | rdtp->dyntick_drain = 0; |
2048 | rdtp->dyntick_holdoff = jiffies; | |
fd4b3526 PM |
2049 | if (rcu_cpu_has_nonlazy_callbacks(cpu)) { |
2050 | trace_rcu_prep_idle("Dyntick with callbacks"); | |
5955f7ee | 2051 | rdtp->idle_gp_timer_expires = |
e84c48ae PM |
2052 | round_up(jiffies + RCU_IDLE_GP_DELAY, |
2053 | RCU_IDLE_GP_DELAY); | |
fd4b3526 | 2054 | } else { |
5955f7ee | 2055 | rdtp->idle_gp_timer_expires = |
e84c48ae | 2056 | round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY); |
fd4b3526 PM |
2057 | trace_rcu_prep_idle("Dyntick with lazy callbacks"); |
2058 | } | |
5955f7ee PM |
2059 | tp = &rdtp->idle_gp_timer; |
2060 | mod_timer_pinned(tp, rdtp->idle_gp_timer_expires); | |
2061 | rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; | |
f23f7fa1 | 2062 | return; /* Nothing more to do immediately. */ |
5955f7ee | 2063 | } else if (--(rdtp->dyntick_drain) <= 0) { |
a47cd880 | 2064 | /* We have hit the limit, so time to give up. */ |
5955f7ee | 2065 | rdtp->dyntick_holdoff = jiffies; |
433cdddc | 2066 | trace_rcu_prep_idle("Begin holdoff"); |
aea1b35e PM |
2067 | invoke_rcu_core(); /* Force the CPU out of dyntick-idle. */ |
2068 | return; | |
a47cd880 PM |
2069 | } |
2070 | ||
aea1b35e PM |
2071 | /* |
2072 | * Do one step of pushing the remaining RCU callbacks through | |
2073 | * the RCU core state machine. | |
2074 | */ | |
2075 | #ifdef CONFIG_TREE_PREEMPT_RCU | |
2076 | if (per_cpu(rcu_preempt_data, cpu).nxtlist) { | |
2077 | rcu_preempt_qs(cpu); | |
2078 | force_quiescent_state(&rcu_preempt_state, 0); | |
aea1b35e PM |
2079 | } |
2080 | #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */ | |
a47cd880 PM |
2081 | if (per_cpu(rcu_sched_data, cpu).nxtlist) { |
2082 | rcu_sched_qs(cpu); | |
2083 | force_quiescent_state(&rcu_sched_state, 0); | |
a47cd880 PM |
2084 | } |
2085 | if (per_cpu(rcu_bh_data, cpu).nxtlist) { | |
2086 | rcu_bh_qs(cpu); | |
2087 | force_quiescent_state(&rcu_bh_state, 0); | |
8bd93a2c PM |
2088 | } |
2089 | ||
433cdddc PM |
2090 | /* |
2091 | * If RCU callbacks are still pending, RCU still needs this CPU. | |
2092 | * So try forcing the callbacks through the grace period. | |
2093 | */ | |
3ad0decf | 2094 | if (rcu_cpu_has_callbacks(cpu)) { |
433cdddc | 2095 | trace_rcu_prep_idle("More callbacks"); |
a46e0899 | 2096 | invoke_rcu_core(); |
c701d5d9 | 2097 | } else { |
433cdddc | 2098 | trace_rcu_prep_idle("Callbacks drained"); |
c701d5d9 | 2099 | } |
8bd93a2c PM |
2100 | } |
2101 | ||
c57afe80 | 2102 | /* |
98248a0e PM |
2103 | * Keep a running count of the number of non-lazy callbacks posted |
2104 | * on this CPU. This running counter (which is never decremented) allows | |
2105 | * rcu_prepare_for_idle() to detect when something out of the idle loop | |
2106 | * posts a callback, even if an equal number of callbacks are invoked. | |
2107 | * Of course, callbacks should only be posted from within a trace event | |
2108 | * designed to be called from idle or from within RCU_NONIDLE(). | |
c57afe80 PM |
2109 | */ |
2110 | static void rcu_idle_count_callbacks_posted(void) | |
2111 | { | |
5955f7ee | 2112 | __this_cpu_add(rcu_dynticks.nonlazy_posted, 1); |
c57afe80 PM |
2113 | } |
2114 | ||
8bd93a2c | 2115 | #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
a858af28 PM |
2116 | |
2117 | #ifdef CONFIG_RCU_CPU_STALL_INFO | |
2118 | ||
2119 | #ifdef CONFIG_RCU_FAST_NO_HZ | |
2120 | ||
2121 | static void print_cpu_stall_fast_no_hz(char *cp, int cpu) | |
2122 | { | |
5955f7ee PM |
2123 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
2124 | struct timer_list *tltp = &rdtp->idle_gp_timer; | |
a858af28 | 2125 | |
2ee3dc80 | 2126 | sprintf(cp, "drain=%d %c timer=%lu", |
5955f7ee PM |
2127 | rdtp->dyntick_drain, |
2128 | rdtp->dyntick_holdoff == jiffies ? 'H' : '.', | |
2ee3dc80 | 2129 | timer_pending(tltp) ? tltp->expires - jiffies : -1); |
a858af28 PM |
2130 | } |
2131 | ||
2132 | #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ | |
2133 | ||
2134 | static void print_cpu_stall_fast_no_hz(char *cp, int cpu) | |
2135 | { | |
1c17e4d4 | 2136 | *cp = '\0'; |
a858af28 PM |
2137 | } |
2138 | ||
2139 | #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ | |
2140 | ||
2141 | /* Initiate the stall-info list. */ | |
2142 | static void print_cpu_stall_info_begin(void) | |
2143 | { | |
2144 | printk(KERN_CONT "\n"); | |
2145 | } | |
2146 | ||
2147 | /* | |
2148 | * Print out diagnostic information for the specified stalled CPU. | |
2149 | * | |
2150 | * If the specified CPU is aware of the current RCU grace period | |
2151 | * (flavor specified by rsp), then print the number of scheduling | |
2152 | * clock interrupts the CPU has taken during the time that it has | |
2153 | * been aware. Otherwise, print the number of RCU grace periods | |
2154 | * that this CPU is ignorant of, for example, "1" if the CPU was | |
2155 | * aware of the previous grace period. | |
2156 | * | |
2157 | * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. | |
2158 | */ | |
2159 | static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) | |
2160 | { | |
2161 | char fast_no_hz[72]; | |
2162 | struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); | |
2163 | struct rcu_dynticks *rdtp = rdp->dynticks; | |
2164 | char *ticks_title; | |
2165 | unsigned long ticks_value; | |
2166 | ||
2167 | if (rsp->gpnum == rdp->gpnum) { | |
2168 | ticks_title = "ticks this GP"; | |
2169 | ticks_value = rdp->ticks_this_gp; | |
2170 | } else { | |
2171 | ticks_title = "GPs behind"; | |
2172 | ticks_value = rsp->gpnum - rdp->gpnum; | |
2173 | } | |
2174 | print_cpu_stall_fast_no_hz(fast_no_hz, cpu); | |
2175 | printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d %s\n", | |
2176 | cpu, ticks_value, ticks_title, | |
2177 | atomic_read(&rdtp->dynticks) & 0xfff, | |
2178 | rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting, | |
2179 | fast_no_hz); | |
2180 | } | |
2181 | ||
2182 | /* Terminate the stall-info list. */ | |
2183 | static void print_cpu_stall_info_end(void) | |
2184 | { | |
2185 | printk(KERN_ERR "\t"); | |
2186 | } | |
2187 | ||
2188 | /* Zero ->ticks_this_gp for all flavors of RCU. */ | |
2189 | static void zero_cpu_stall_ticks(struct rcu_data *rdp) | |
2190 | { | |
2191 | rdp->ticks_this_gp = 0; | |
2192 | } | |
2193 | ||
2194 | /* Increment ->ticks_this_gp for all flavors of RCU. */ | |
2195 | static void increment_cpu_stall_ticks(void) | |
2196 | { | |
2197 | __get_cpu_var(rcu_sched_data).ticks_this_gp++; | |
2198 | __get_cpu_var(rcu_bh_data).ticks_this_gp++; | |
2199 | #ifdef CONFIG_TREE_PREEMPT_RCU | |
2200 | __get_cpu_var(rcu_preempt_data).ticks_this_gp++; | |
2201 | #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */ | |
2202 | } | |
2203 | ||
2204 | #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ | |
2205 | ||
2206 | static void print_cpu_stall_info_begin(void) | |
2207 | { | |
2208 | printk(KERN_CONT " {"); | |
2209 | } | |
2210 | ||
2211 | static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) | |
2212 | { | |
2213 | printk(KERN_CONT " %d", cpu); | |
2214 | } | |
2215 | ||
2216 | static void print_cpu_stall_info_end(void) | |
2217 | { | |
2218 | printk(KERN_CONT "} "); | |
2219 | } | |
2220 | ||
2221 | static void zero_cpu_stall_ticks(struct rcu_data *rdp) | |
2222 | { | |
2223 | } | |
2224 | ||
2225 | static void increment_cpu_stall_ticks(void) | |
2226 | { | |
2227 | } | |
2228 | ||
2229 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ |