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f41d911f PM |
1 | /* |
2 | * Read-Copy Update mechanism for mutual exclusion (tree-based version) | |
3 | * Internal non-public definitions that provide either classic | |
4 | * or preemptable semantics. | |
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> |
7b27d547 | 28 | #include <linux/stop_machine.h> |
f41d911f | 29 | |
26845c28 PM |
30 | /* |
31 | * Check the RCU kernel configuration parameters and print informative | |
32 | * messages about anything out of the ordinary. If you like #ifdef, you | |
33 | * will love this function. | |
34 | */ | |
35 | static void __init rcu_bootup_announce_oddness(void) | |
36 | { | |
37 | #ifdef CONFIG_RCU_TRACE | |
38 | printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n"); | |
39 | #endif | |
40 | #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32) | |
41 | printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n", | |
42 | CONFIG_RCU_FANOUT); | |
43 | #endif | |
44 | #ifdef CONFIG_RCU_FANOUT_EXACT | |
45 | printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n"); | |
46 | #endif | |
47 | #ifdef CONFIG_RCU_FAST_NO_HZ | |
48 | printk(KERN_INFO | |
49 | "\tRCU dyntick-idle grace-period acceleration is enabled.\n"); | |
50 | #endif | |
51 | #ifdef CONFIG_PROVE_RCU | |
52 | printk(KERN_INFO "\tRCU lockdep checking is enabled.\n"); | |
53 | #endif | |
54 | #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE | |
55 | printk(KERN_INFO "\tRCU torture testing starts during boot.\n"); | |
56 | #endif | |
57 | #ifndef CONFIG_RCU_CPU_STALL_DETECTOR | |
58 | printk(KERN_INFO | |
59 | "\tRCU-based detection of stalled CPUs is disabled.\n"); | |
60 | #endif | |
81a294c4 | 61 | #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE) |
26845c28 PM |
62 | printk(KERN_INFO "\tVerbose stalled-CPUs detection is disabled.\n"); |
63 | #endif | |
64 | #if NUM_RCU_LVL_4 != 0 | |
65 | printk(KERN_INFO "\tExperimental four-level hierarchy is enabled.\n"); | |
66 | #endif | |
67 | } | |
68 | ||
f41d911f PM |
69 | #ifdef CONFIG_TREE_PREEMPT_RCU |
70 | ||
71 | struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state); | |
72 | DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data); | |
73 | ||
d9a3da06 PM |
74 | static int rcu_preempted_readers_exp(struct rcu_node *rnp); |
75 | ||
f41d911f PM |
76 | /* |
77 | * Tell them what RCU they are running. | |
78 | */ | |
0e0fc1c2 | 79 | static void __init rcu_bootup_announce(void) |
f41d911f | 80 | { |
26845c28 PM |
81 | printk(KERN_INFO "Preemptable hierarchical RCU implementation.\n"); |
82 | rcu_bootup_announce_oddness(); | |
f41d911f PM |
83 | } |
84 | ||
85 | /* | |
86 | * Return the number of RCU-preempt batches processed thus far | |
87 | * for debug and statistics. | |
88 | */ | |
89 | long rcu_batches_completed_preempt(void) | |
90 | { | |
91 | return rcu_preempt_state.completed; | |
92 | } | |
93 | EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt); | |
94 | ||
95 | /* | |
96 | * Return the number of RCU batches processed thus far for debug & stats. | |
97 | */ | |
98 | long rcu_batches_completed(void) | |
99 | { | |
100 | return rcu_batches_completed_preempt(); | |
101 | } | |
102 | EXPORT_SYMBOL_GPL(rcu_batches_completed); | |
103 | ||
bf66f18e PM |
104 | /* |
105 | * Force a quiescent state for preemptible RCU. | |
106 | */ | |
107 | void rcu_force_quiescent_state(void) | |
108 | { | |
109 | force_quiescent_state(&rcu_preempt_state, 0); | |
110 | } | |
111 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); | |
112 | ||
f41d911f PM |
113 | /* |
114 | * Record a preemptable-RCU quiescent state for the specified CPU. Note | |
115 | * that this just means that the task currently running on the CPU is | |
116 | * not in a quiescent state. There might be any number of tasks blocked | |
117 | * while in an RCU read-side critical section. | |
25502a6c PM |
118 | * |
119 | * Unlike the other rcu_*_qs() functions, callers to this function | |
120 | * must disable irqs in order to protect the assignment to | |
121 | * ->rcu_read_unlock_special. | |
f41d911f | 122 | */ |
c3422bea | 123 | static void rcu_preempt_qs(int cpu) |
f41d911f PM |
124 | { |
125 | struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); | |
25502a6c | 126 | |
c64ac3ce | 127 | rdp->passed_quiesc_completed = rdp->gpnum - 1; |
c3422bea PM |
128 | barrier(); |
129 | rdp->passed_quiesc = 1; | |
25502a6c | 130 | current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; |
f41d911f PM |
131 | } |
132 | ||
133 | /* | |
c3422bea PM |
134 | * We have entered the scheduler, and the current task might soon be |
135 | * context-switched away from. If this task is in an RCU read-side | |
136 | * critical section, we will no longer be able to rely on the CPU to | |
137 | * record that fact, so we enqueue the task on the appropriate entry | |
138 | * of the blocked_tasks[] array. The task will dequeue itself when | |
139 | * it exits the outermost enclosing RCU read-side critical section. | |
140 | * Therefore, the current grace period cannot be permitted to complete | |
141 | * until the blocked_tasks[] entry indexed by the low-order bit of | |
142 | * rnp->gpnum empties. | |
143 | * | |
144 | * Caller must disable preemption. | |
f41d911f | 145 | */ |
c3422bea | 146 | static void rcu_preempt_note_context_switch(int cpu) |
f41d911f PM |
147 | { |
148 | struct task_struct *t = current; | |
c3422bea | 149 | unsigned long flags; |
f41d911f PM |
150 | int phase; |
151 | struct rcu_data *rdp; | |
152 | struct rcu_node *rnp; | |
153 | ||
154 | if (t->rcu_read_lock_nesting && | |
155 | (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { | |
156 | ||
157 | /* Possibly blocking in an RCU read-side critical section. */ | |
394f99a9 | 158 | rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu); |
f41d911f | 159 | rnp = rdp->mynode; |
1304afb2 | 160 | raw_spin_lock_irqsave(&rnp->lock, flags); |
f41d911f | 161 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; |
86848966 | 162 | t->rcu_blocked_node = rnp; |
f41d911f PM |
163 | |
164 | /* | |
165 | * If this CPU has already checked in, then this task | |
166 | * will hold up the next grace period rather than the | |
167 | * current grace period. Queue the task accordingly. | |
168 | * If the task is queued for the current grace period | |
169 | * (i.e., this CPU has not yet passed through a quiescent | |
170 | * state for the current grace period), then as long | |
171 | * as that task remains queued, the current grace period | |
172 | * cannot end. | |
b0e165c0 PM |
173 | * |
174 | * But first, note that the current CPU must still be | |
175 | * on line! | |
f41d911f | 176 | */ |
b0e165c0 | 177 | WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); |
e7d8842e PM |
178 | WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); |
179 | phase = (rnp->gpnum + !(rnp->qsmask & rdp->grpmask)) & 0x1; | |
f41d911f | 180 | list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]); |
1304afb2 | 181 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
f41d911f PM |
182 | } |
183 | ||
184 | /* | |
185 | * Either we were not in an RCU read-side critical section to | |
186 | * begin with, or we have now recorded that critical section | |
187 | * globally. Either way, we can now note a quiescent state | |
188 | * for this CPU. Again, if we were in an RCU read-side critical | |
189 | * section, and if that critical section was blocking the current | |
190 | * grace period, then the fact that the task has been enqueued | |
191 | * means that we continue to block the current grace period. | |
192 | */ | |
e7d8842e | 193 | local_irq_save(flags); |
25502a6c | 194 | rcu_preempt_qs(cpu); |
e7d8842e | 195 | local_irq_restore(flags); |
f41d911f PM |
196 | } |
197 | ||
198 | /* | |
199 | * Tree-preemptable RCU implementation for rcu_read_lock(). | |
200 | * Just increment ->rcu_read_lock_nesting, shared state will be updated | |
201 | * if we block. | |
202 | */ | |
203 | void __rcu_read_lock(void) | |
204 | { | |
80dcf60e | 205 | current->rcu_read_lock_nesting++; |
f41d911f PM |
206 | barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */ |
207 | } | |
208 | EXPORT_SYMBOL_GPL(__rcu_read_lock); | |
209 | ||
fc2219d4 PM |
210 | /* |
211 | * Check for preempted RCU readers blocking the current grace period | |
212 | * for the specified rcu_node structure. If the caller needs a reliable | |
213 | * answer, it must hold the rcu_node's ->lock. | |
214 | */ | |
215 | static int rcu_preempted_readers(struct rcu_node *rnp) | |
216 | { | |
d9a3da06 PM |
217 | int phase = rnp->gpnum & 0x1; |
218 | ||
219 | return !list_empty(&rnp->blocked_tasks[phase]) || | |
220 | !list_empty(&rnp->blocked_tasks[phase + 2]); | |
fc2219d4 PM |
221 | } |
222 | ||
b668c9cf PM |
223 | /* |
224 | * Record a quiescent state for all tasks that were previously queued | |
225 | * on the specified rcu_node structure and that were blocking the current | |
226 | * RCU grace period. The caller must hold the specified rnp->lock with | |
227 | * irqs disabled, and this lock is released upon return, but irqs remain | |
228 | * disabled. | |
229 | */ | |
d3f6bad3 | 230 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
b668c9cf PM |
231 | __releases(rnp->lock) |
232 | { | |
233 | unsigned long mask; | |
234 | struct rcu_node *rnp_p; | |
235 | ||
236 | if (rnp->qsmask != 0 || rcu_preempted_readers(rnp)) { | |
1304afb2 | 237 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b668c9cf PM |
238 | return; /* Still need more quiescent states! */ |
239 | } | |
240 | ||
241 | rnp_p = rnp->parent; | |
242 | if (rnp_p == NULL) { | |
243 | /* | |
244 | * Either there is only one rcu_node in the tree, | |
245 | * or tasks were kicked up to root rcu_node due to | |
246 | * CPUs going offline. | |
247 | */ | |
d3f6bad3 | 248 | rcu_report_qs_rsp(&rcu_preempt_state, flags); |
b668c9cf PM |
249 | return; |
250 | } | |
251 | ||
252 | /* Report up the rest of the hierarchy. */ | |
253 | mask = rnp->grpmask; | |
1304afb2 PM |
254 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
255 | raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */ | |
d3f6bad3 | 256 | rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags); |
b668c9cf PM |
257 | } |
258 | ||
259 | /* | |
260 | * Handle special cases during rcu_read_unlock(), such as needing to | |
261 | * notify RCU core processing or task having blocked during the RCU | |
262 | * read-side critical section. | |
263 | */ | |
f41d911f PM |
264 | static void rcu_read_unlock_special(struct task_struct *t) |
265 | { | |
266 | int empty; | |
d9a3da06 | 267 | int empty_exp; |
f41d911f | 268 | unsigned long flags; |
f41d911f PM |
269 | struct rcu_node *rnp; |
270 | int special; | |
271 | ||
272 | /* NMI handlers cannot block and cannot safely manipulate state. */ | |
273 | if (in_nmi()) | |
274 | return; | |
275 | ||
276 | local_irq_save(flags); | |
277 | ||
278 | /* | |
279 | * If RCU core is waiting for this CPU to exit critical section, | |
280 | * let it know that we have done so. | |
281 | */ | |
282 | special = t->rcu_read_unlock_special; | |
283 | if (special & RCU_READ_UNLOCK_NEED_QS) { | |
c3422bea | 284 | rcu_preempt_qs(smp_processor_id()); |
f41d911f PM |
285 | } |
286 | ||
287 | /* Hardware IRQ handlers cannot block. */ | |
288 | if (in_irq()) { | |
289 | local_irq_restore(flags); | |
290 | return; | |
291 | } | |
292 | ||
293 | /* Clean up if blocked during RCU read-side critical section. */ | |
294 | if (special & RCU_READ_UNLOCK_BLOCKED) { | |
295 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; | |
296 | ||
dd5d19ba PM |
297 | /* |
298 | * Remove this task from the list it blocked on. The | |
299 | * task can migrate while we acquire the lock, but at | |
300 | * most one time. So at most two passes through loop. | |
301 | */ | |
302 | for (;;) { | |
86848966 | 303 | rnp = t->rcu_blocked_node; |
1304afb2 | 304 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
86848966 | 305 | if (rnp == t->rcu_blocked_node) |
dd5d19ba | 306 | break; |
1304afb2 | 307 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
dd5d19ba | 308 | } |
fc2219d4 | 309 | empty = !rcu_preempted_readers(rnp); |
d9a3da06 PM |
310 | empty_exp = !rcu_preempted_readers_exp(rnp); |
311 | smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ | |
f41d911f | 312 | list_del_init(&t->rcu_node_entry); |
dd5d19ba | 313 | t->rcu_blocked_node = NULL; |
f41d911f PM |
314 | |
315 | /* | |
316 | * If this was the last task on the current list, and if | |
317 | * we aren't waiting on any CPUs, report the quiescent state. | |
d3f6bad3 | 318 | * Note that rcu_report_unblock_qs_rnp() releases rnp->lock. |
f41d911f | 319 | */ |
b668c9cf | 320 | if (empty) |
1304afb2 | 321 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b668c9cf | 322 | else |
d3f6bad3 | 323 | rcu_report_unblock_qs_rnp(rnp, flags); |
d9a3da06 PM |
324 | |
325 | /* | |
326 | * If this was the last task on the expedited lists, | |
327 | * then we need to report up the rcu_node hierarchy. | |
328 | */ | |
329 | if (!empty_exp && !rcu_preempted_readers_exp(rnp)) | |
330 | rcu_report_exp_rnp(&rcu_preempt_state, rnp); | |
b668c9cf PM |
331 | } else { |
332 | local_irq_restore(flags); | |
f41d911f | 333 | } |
f41d911f PM |
334 | } |
335 | ||
336 | /* | |
337 | * Tree-preemptable RCU implementation for rcu_read_unlock(). | |
338 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost | |
339 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then | |
340 | * invoke rcu_read_unlock_special() to clean up after a context switch | |
341 | * in an RCU read-side critical section and other special cases. | |
342 | */ | |
343 | void __rcu_read_unlock(void) | |
344 | { | |
345 | struct task_struct *t = current; | |
346 | ||
347 | barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */ | |
80dcf60e PM |
348 | --t->rcu_read_lock_nesting; |
349 | barrier(); /* decrement before load of ->rcu_read_unlock_special */ | |
350 | if (t->rcu_read_lock_nesting == 0 && | |
f41d911f PM |
351 | unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) |
352 | rcu_read_unlock_special(t); | |
cba8244a PM |
353 | #ifdef CONFIG_PROVE_LOCKING |
354 | WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0); | |
355 | #endif /* #ifdef CONFIG_PROVE_LOCKING */ | |
f41d911f PM |
356 | } |
357 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); | |
358 | ||
359 | #ifdef CONFIG_RCU_CPU_STALL_DETECTOR | |
360 | ||
1ed509a2 PM |
361 | #ifdef CONFIG_RCU_CPU_STALL_VERBOSE |
362 | ||
363 | /* | |
364 | * Dump detailed information for all tasks blocking the current RCU | |
365 | * grace period on the specified rcu_node structure. | |
366 | */ | |
367 | static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) | |
368 | { | |
369 | unsigned long flags; | |
370 | struct list_head *lp; | |
371 | int phase; | |
372 | struct task_struct *t; | |
373 | ||
374 | if (rcu_preempted_readers(rnp)) { | |
375 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
376 | phase = rnp->gpnum & 0x1; | |
377 | lp = &rnp->blocked_tasks[phase]; | |
378 | list_for_each_entry(t, lp, rcu_node_entry) | |
379 | sched_show_task(t); | |
380 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
381 | } | |
382 | } | |
383 | ||
384 | /* | |
385 | * Dump detailed information for all tasks blocking the current RCU | |
386 | * grace period. | |
387 | */ | |
388 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
389 | { | |
390 | struct rcu_node *rnp = rcu_get_root(rsp); | |
391 | ||
392 | rcu_print_detail_task_stall_rnp(rnp); | |
393 | rcu_for_each_leaf_node(rsp, rnp) | |
394 | rcu_print_detail_task_stall_rnp(rnp); | |
395 | } | |
396 | ||
397 | #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ | |
398 | ||
399 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
400 | { | |
401 | } | |
402 | ||
403 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ | |
404 | ||
f41d911f PM |
405 | /* |
406 | * Scan the current list of tasks blocked within RCU read-side critical | |
407 | * sections, printing out the tid of each. | |
408 | */ | |
409 | static void rcu_print_task_stall(struct rcu_node *rnp) | |
410 | { | |
f41d911f | 411 | struct list_head *lp; |
fc2219d4 | 412 | int phase; |
f41d911f PM |
413 | struct task_struct *t; |
414 | ||
fc2219d4 | 415 | if (rcu_preempted_readers(rnp)) { |
fc2219d4 | 416 | phase = rnp->gpnum & 0x1; |
f41d911f PM |
417 | lp = &rnp->blocked_tasks[phase]; |
418 | list_for_each_entry(t, lp, rcu_node_entry) | |
419 | printk(" P%d", t->pid); | |
f41d911f PM |
420 | } |
421 | } | |
422 | ||
53d84e00 PM |
423 | /* |
424 | * Suppress preemptible RCU's CPU stall warnings by pushing the | |
425 | * time of the next stall-warning message comfortably far into the | |
426 | * future. | |
427 | */ | |
428 | static void rcu_preempt_stall_reset(void) | |
429 | { | |
430 | rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2; | |
431 | } | |
432 | ||
f41d911f PM |
433 | #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ |
434 | ||
b0e165c0 PM |
435 | /* |
436 | * Check that the list of blocked tasks for the newly completed grace | |
437 | * period is in fact empty. It is a serious bug to complete a grace | |
438 | * period that still has RCU readers blocked! This function must be | |
439 | * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock | |
440 | * must be held by the caller. | |
441 | */ | |
442 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
443 | { | |
fc2219d4 | 444 | WARN_ON_ONCE(rcu_preempted_readers(rnp)); |
28ecd580 | 445 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
446 | } |
447 | ||
33f76148 PM |
448 | #ifdef CONFIG_HOTPLUG_CPU |
449 | ||
dd5d19ba PM |
450 | /* |
451 | * Handle tasklist migration for case in which all CPUs covered by the | |
452 | * specified rcu_node have gone offline. Move them up to the root | |
453 | * rcu_node. The reason for not just moving them to the immediate | |
454 | * parent is to remove the need for rcu_read_unlock_special() to | |
455 | * make more than two attempts to acquire the target rcu_node's lock. | |
b668c9cf PM |
456 | * Returns true if there were tasks blocking the current RCU grace |
457 | * period. | |
dd5d19ba | 458 | * |
237c80c5 PM |
459 | * Returns 1 if there was previously a task blocking the current grace |
460 | * period on the specified rcu_node structure. | |
461 | * | |
dd5d19ba PM |
462 | * The caller must hold rnp->lock with irqs disabled. |
463 | */ | |
237c80c5 PM |
464 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
465 | struct rcu_node *rnp, | |
466 | struct rcu_data *rdp) | |
dd5d19ba PM |
467 | { |
468 | int i; | |
469 | struct list_head *lp; | |
470 | struct list_head *lp_root; | |
d9a3da06 | 471 | int retval = 0; |
dd5d19ba PM |
472 | struct rcu_node *rnp_root = rcu_get_root(rsp); |
473 | struct task_struct *tp; | |
474 | ||
86848966 PM |
475 | if (rnp == rnp_root) { |
476 | WARN_ONCE(1, "Last CPU thought to be offlined?"); | |
237c80c5 | 477 | return 0; /* Shouldn't happen: at least one CPU online. */ |
86848966 | 478 | } |
28ecd580 PM |
479 | WARN_ON_ONCE(rnp != rdp->mynode && |
480 | (!list_empty(&rnp->blocked_tasks[0]) || | |
d9a3da06 PM |
481 | !list_empty(&rnp->blocked_tasks[1]) || |
482 | !list_empty(&rnp->blocked_tasks[2]) || | |
483 | !list_empty(&rnp->blocked_tasks[3]))); | |
dd5d19ba PM |
484 | |
485 | /* | |
486 | * Move tasks up to root rcu_node. Rely on the fact that the | |
487 | * root rcu_node can be at most one ahead of the rest of the | |
488 | * rcu_nodes in terms of gp_num value. This fact allows us to | |
489 | * move the blocked_tasks[] array directly, element by element. | |
490 | */ | |
d9a3da06 PM |
491 | if (rcu_preempted_readers(rnp)) |
492 | retval |= RCU_OFL_TASKS_NORM_GP; | |
493 | if (rcu_preempted_readers_exp(rnp)) | |
494 | retval |= RCU_OFL_TASKS_EXP_GP; | |
495 | for (i = 0; i < 4; i++) { | |
dd5d19ba PM |
496 | lp = &rnp->blocked_tasks[i]; |
497 | lp_root = &rnp_root->blocked_tasks[i]; | |
498 | while (!list_empty(lp)) { | |
499 | tp = list_entry(lp->next, typeof(*tp), rcu_node_entry); | |
1304afb2 | 500 | raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ |
dd5d19ba PM |
501 | list_del(&tp->rcu_node_entry); |
502 | tp->rcu_blocked_node = rnp_root; | |
503 | list_add(&tp->rcu_node_entry, lp_root); | |
1304afb2 | 504 | raw_spin_unlock(&rnp_root->lock); /* irqs remain disabled */ |
dd5d19ba PM |
505 | } |
506 | } | |
237c80c5 | 507 | return retval; |
dd5d19ba PM |
508 | } |
509 | ||
33f76148 PM |
510 | /* |
511 | * Do CPU-offline processing for preemptable RCU. | |
512 | */ | |
513 | static void rcu_preempt_offline_cpu(int cpu) | |
514 | { | |
515 | __rcu_offline_cpu(cpu, &rcu_preempt_state); | |
516 | } | |
517 | ||
518 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
519 | ||
f41d911f PM |
520 | /* |
521 | * Check for a quiescent state from the current CPU. When a task blocks, | |
522 | * the task is recorded in the corresponding CPU's rcu_node structure, | |
523 | * which is checked elsewhere. | |
524 | * | |
525 | * Caller must disable hard irqs. | |
526 | */ | |
527 | static void rcu_preempt_check_callbacks(int cpu) | |
528 | { | |
529 | struct task_struct *t = current; | |
530 | ||
531 | if (t->rcu_read_lock_nesting == 0) { | |
c3422bea | 532 | rcu_preempt_qs(cpu); |
f41d911f PM |
533 | return; |
534 | } | |
a71fca58 | 535 | if (per_cpu(rcu_preempt_data, cpu).qs_pending) |
c3422bea | 536 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; |
f41d911f PM |
537 | } |
538 | ||
539 | /* | |
540 | * Process callbacks for preemptable RCU. | |
541 | */ | |
542 | static void rcu_preempt_process_callbacks(void) | |
543 | { | |
544 | __rcu_process_callbacks(&rcu_preempt_state, | |
545 | &__get_cpu_var(rcu_preempt_data)); | |
546 | } | |
547 | ||
548 | /* | |
549 | * Queue a preemptable-RCU callback for invocation after a grace period. | |
550 | */ | |
551 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) | |
552 | { | |
553 | __call_rcu(head, func, &rcu_preempt_state); | |
554 | } | |
555 | EXPORT_SYMBOL_GPL(call_rcu); | |
556 | ||
6ebb237b PM |
557 | /** |
558 | * synchronize_rcu - wait until a grace period has elapsed. | |
559 | * | |
560 | * Control will return to the caller some time after a full grace | |
561 | * period has elapsed, in other words after all currently executing RCU | |
77d8485a PM |
562 | * read-side critical sections have completed. Note, however, that |
563 | * upon return from synchronize_rcu(), the caller might well be executing | |
564 | * concurrently with new RCU read-side critical sections that began while | |
565 | * synchronize_rcu() was waiting. RCU read-side critical sections are | |
566 | * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. | |
6ebb237b PM |
567 | */ |
568 | void synchronize_rcu(void) | |
569 | { | |
570 | struct rcu_synchronize rcu; | |
571 | ||
572 | if (!rcu_scheduler_active) | |
573 | return; | |
574 | ||
72d5a9f7 | 575 | init_rcu_head_on_stack(&rcu.head); |
6ebb237b PM |
576 | init_completion(&rcu.completion); |
577 | /* Will wake me after RCU finished. */ | |
578 | call_rcu(&rcu.head, wakeme_after_rcu); | |
579 | /* Wait for it. */ | |
580 | wait_for_completion(&rcu.completion); | |
72d5a9f7 | 581 | destroy_rcu_head_on_stack(&rcu.head); |
6ebb237b PM |
582 | } |
583 | EXPORT_SYMBOL_GPL(synchronize_rcu); | |
584 | ||
d9a3da06 PM |
585 | static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); |
586 | static long sync_rcu_preempt_exp_count; | |
587 | static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); | |
588 | ||
589 | /* | |
590 | * Return non-zero if there are any tasks in RCU read-side critical | |
591 | * sections blocking the current preemptible-RCU expedited grace period. | |
592 | * If there is no preemptible-RCU expedited grace period currently in | |
593 | * progress, returns zero unconditionally. | |
594 | */ | |
595 | static int rcu_preempted_readers_exp(struct rcu_node *rnp) | |
596 | { | |
597 | return !list_empty(&rnp->blocked_tasks[2]) || | |
598 | !list_empty(&rnp->blocked_tasks[3]); | |
599 | } | |
600 | ||
601 | /* | |
602 | * return non-zero if there is no RCU expedited grace period in progress | |
603 | * for the specified rcu_node structure, in other words, if all CPUs and | |
604 | * tasks covered by the specified rcu_node structure have done their bit | |
605 | * for the current expedited grace period. Works only for preemptible | |
606 | * RCU -- other RCU implementation use other means. | |
607 | * | |
608 | * Caller must hold sync_rcu_preempt_exp_mutex. | |
609 | */ | |
610 | static int sync_rcu_preempt_exp_done(struct rcu_node *rnp) | |
611 | { | |
612 | return !rcu_preempted_readers_exp(rnp) && | |
613 | ACCESS_ONCE(rnp->expmask) == 0; | |
614 | } | |
615 | ||
616 | /* | |
617 | * Report the exit from RCU read-side critical section for the last task | |
618 | * that queued itself during or before the current expedited preemptible-RCU | |
619 | * grace period. This event is reported either to the rcu_node structure on | |
620 | * which the task was queued or to one of that rcu_node structure's ancestors, | |
621 | * recursively up the tree. (Calm down, calm down, we do the recursion | |
622 | * iteratively!) | |
623 | * | |
624 | * Caller must hold sync_rcu_preempt_exp_mutex. | |
625 | */ | |
626 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) | |
627 | { | |
628 | unsigned long flags; | |
629 | unsigned long mask; | |
630 | ||
1304afb2 | 631 | raw_spin_lock_irqsave(&rnp->lock, flags); |
d9a3da06 PM |
632 | for (;;) { |
633 | if (!sync_rcu_preempt_exp_done(rnp)) | |
634 | break; | |
635 | if (rnp->parent == NULL) { | |
636 | wake_up(&sync_rcu_preempt_exp_wq); | |
637 | break; | |
638 | } | |
639 | mask = rnp->grpmask; | |
1304afb2 | 640 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ |
d9a3da06 | 641 | rnp = rnp->parent; |
1304afb2 | 642 | raw_spin_lock(&rnp->lock); /* irqs already disabled */ |
d9a3da06 PM |
643 | rnp->expmask &= ~mask; |
644 | } | |
1304afb2 | 645 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
d9a3da06 PM |
646 | } |
647 | ||
648 | /* | |
649 | * Snapshot the tasks blocking the newly started preemptible-RCU expedited | |
650 | * grace period for the specified rcu_node structure. If there are no such | |
651 | * tasks, report it up the rcu_node hierarchy. | |
652 | * | |
653 | * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock. | |
654 | */ | |
655 | static void | |
656 | sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) | |
657 | { | |
658 | int must_wait; | |
659 | ||
1304afb2 | 660 | raw_spin_lock(&rnp->lock); /* irqs already disabled */ |
d9a3da06 PM |
661 | list_splice_init(&rnp->blocked_tasks[0], &rnp->blocked_tasks[2]); |
662 | list_splice_init(&rnp->blocked_tasks[1], &rnp->blocked_tasks[3]); | |
663 | must_wait = rcu_preempted_readers_exp(rnp); | |
1304afb2 | 664 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ |
d9a3da06 PM |
665 | if (!must_wait) |
666 | rcu_report_exp_rnp(rsp, rnp); | |
667 | } | |
668 | ||
019129d5 | 669 | /* |
d9a3da06 PM |
670 | * Wait for an rcu-preempt grace period, but expedite it. The basic idea |
671 | * is to invoke synchronize_sched_expedited() to push all the tasks to | |
672 | * the ->blocked_tasks[] lists, move all entries from the first set of | |
673 | * ->blocked_tasks[] lists to the second set, and finally wait for this | |
674 | * second set to drain. | |
019129d5 PM |
675 | */ |
676 | void synchronize_rcu_expedited(void) | |
677 | { | |
d9a3da06 PM |
678 | unsigned long flags; |
679 | struct rcu_node *rnp; | |
680 | struct rcu_state *rsp = &rcu_preempt_state; | |
681 | long snap; | |
682 | int trycount = 0; | |
683 | ||
684 | smp_mb(); /* Caller's modifications seen first by other CPUs. */ | |
685 | snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1; | |
686 | smp_mb(); /* Above access cannot bleed into critical section. */ | |
687 | ||
688 | /* | |
689 | * Acquire lock, falling back to synchronize_rcu() if too many | |
690 | * lock-acquisition failures. Of course, if someone does the | |
691 | * expedited grace period for us, just leave. | |
692 | */ | |
693 | while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) { | |
694 | if (trycount++ < 10) | |
695 | udelay(trycount * num_online_cpus()); | |
696 | else { | |
697 | synchronize_rcu(); | |
698 | return; | |
699 | } | |
700 | if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0) | |
701 | goto mb_ret; /* Others did our work for us. */ | |
702 | } | |
703 | if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0) | |
704 | goto unlock_mb_ret; /* Others did our work for us. */ | |
705 | ||
706 | /* force all RCU readers onto blocked_tasks[]. */ | |
707 | synchronize_sched_expedited(); | |
708 | ||
1304afb2 | 709 | raw_spin_lock_irqsave(&rsp->onofflock, flags); |
d9a3da06 PM |
710 | |
711 | /* Initialize ->expmask for all non-leaf rcu_node structures. */ | |
712 | rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) { | |
1304afb2 | 713 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
d9a3da06 | 714 | rnp->expmask = rnp->qsmaskinit; |
1304afb2 | 715 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
d9a3da06 PM |
716 | } |
717 | ||
718 | /* Snapshot current state of ->blocked_tasks[] lists. */ | |
719 | rcu_for_each_leaf_node(rsp, rnp) | |
720 | sync_rcu_preempt_exp_init(rsp, rnp); | |
721 | if (NUM_RCU_NODES > 1) | |
722 | sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp)); | |
723 | ||
1304afb2 | 724 | raw_spin_unlock_irqrestore(&rsp->onofflock, flags); |
d9a3da06 PM |
725 | |
726 | /* Wait for snapshotted ->blocked_tasks[] lists to drain. */ | |
727 | rnp = rcu_get_root(rsp); | |
728 | wait_event(sync_rcu_preempt_exp_wq, | |
729 | sync_rcu_preempt_exp_done(rnp)); | |
730 | ||
731 | /* Clean up and exit. */ | |
732 | smp_mb(); /* ensure expedited GP seen before counter increment. */ | |
733 | ACCESS_ONCE(sync_rcu_preempt_exp_count)++; | |
734 | unlock_mb_ret: | |
735 | mutex_unlock(&sync_rcu_preempt_exp_mutex); | |
736 | mb_ret: | |
737 | smp_mb(); /* ensure subsequent action seen after grace period. */ | |
019129d5 PM |
738 | } |
739 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
740 | ||
f41d911f PM |
741 | /* |
742 | * Check to see if there is any immediate preemptable-RCU-related work | |
743 | * to be done. | |
744 | */ | |
745 | static int rcu_preempt_pending(int cpu) | |
746 | { | |
747 | return __rcu_pending(&rcu_preempt_state, | |
748 | &per_cpu(rcu_preempt_data, cpu)); | |
749 | } | |
750 | ||
751 | /* | |
752 | * Does preemptable RCU need the CPU to stay out of dynticks mode? | |
753 | */ | |
754 | static int rcu_preempt_needs_cpu(int cpu) | |
755 | { | |
756 | return !!per_cpu(rcu_preempt_data, cpu).nxtlist; | |
757 | } | |
758 | ||
e74f4c45 PM |
759 | /** |
760 | * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. | |
761 | */ | |
762 | void rcu_barrier(void) | |
763 | { | |
764 | _rcu_barrier(&rcu_preempt_state, call_rcu); | |
765 | } | |
766 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
767 | ||
f41d911f PM |
768 | /* |
769 | * Initialize preemptable RCU's per-CPU data. | |
770 | */ | |
771 | static void __cpuinit rcu_preempt_init_percpu_data(int cpu) | |
772 | { | |
773 | rcu_init_percpu_data(cpu, &rcu_preempt_state, 1); | |
774 | } | |
775 | ||
e74f4c45 | 776 | /* |
2d999e03 | 777 | * Move preemptable RCU's callbacks from dying CPU to other online CPU. |
e74f4c45 | 778 | */ |
29494be7 | 779 | static void rcu_preempt_send_cbs_to_online(void) |
e74f4c45 | 780 | { |
29494be7 | 781 | rcu_send_cbs_to_online(&rcu_preempt_state); |
e74f4c45 PM |
782 | } |
783 | ||
1eba8f84 PM |
784 | /* |
785 | * Initialize preemptable RCU's state structures. | |
786 | */ | |
787 | static void __init __rcu_init_preempt(void) | |
788 | { | |
394f99a9 | 789 | rcu_init_one(&rcu_preempt_state, &rcu_preempt_data); |
1eba8f84 PM |
790 | } |
791 | ||
f41d911f PM |
792 | /* |
793 | * Check for a task exiting while in a preemptable-RCU read-side | |
794 | * critical section, clean up if so. No need to issue warnings, | |
795 | * as debug_check_no_locks_held() already does this if lockdep | |
796 | * is enabled. | |
797 | */ | |
798 | void exit_rcu(void) | |
799 | { | |
800 | struct task_struct *t = current; | |
801 | ||
802 | if (t->rcu_read_lock_nesting == 0) | |
803 | return; | |
804 | t->rcu_read_lock_nesting = 1; | |
805 | rcu_read_unlock(); | |
806 | } | |
807 | ||
808 | #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ | |
809 | ||
810 | /* | |
811 | * Tell them what RCU they are running. | |
812 | */ | |
0e0fc1c2 | 813 | static void __init rcu_bootup_announce(void) |
f41d911f PM |
814 | { |
815 | printk(KERN_INFO "Hierarchical RCU implementation.\n"); | |
26845c28 | 816 | rcu_bootup_announce_oddness(); |
f41d911f PM |
817 | } |
818 | ||
819 | /* | |
820 | * Return the number of RCU batches processed thus far for debug & stats. | |
821 | */ | |
822 | long rcu_batches_completed(void) | |
823 | { | |
824 | return rcu_batches_completed_sched(); | |
825 | } | |
826 | EXPORT_SYMBOL_GPL(rcu_batches_completed); | |
827 | ||
bf66f18e PM |
828 | /* |
829 | * Force a quiescent state for RCU, which, because there is no preemptible | |
830 | * RCU, becomes the same as rcu-sched. | |
831 | */ | |
832 | void rcu_force_quiescent_state(void) | |
833 | { | |
834 | rcu_sched_force_quiescent_state(); | |
835 | } | |
836 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); | |
837 | ||
f41d911f PM |
838 | /* |
839 | * Because preemptable RCU does not exist, we never have to check for | |
840 | * CPUs being in quiescent states. | |
841 | */ | |
c3422bea | 842 | static void rcu_preempt_note_context_switch(int cpu) |
f41d911f PM |
843 | { |
844 | } | |
845 | ||
fc2219d4 PM |
846 | /* |
847 | * Because preemptable RCU does not exist, there are never any preempted | |
848 | * RCU readers. | |
849 | */ | |
850 | static int rcu_preempted_readers(struct rcu_node *rnp) | |
851 | { | |
852 | return 0; | |
853 | } | |
854 | ||
b668c9cf PM |
855 | #ifdef CONFIG_HOTPLUG_CPU |
856 | ||
857 | /* Because preemptible RCU does not exist, no quieting of tasks. */ | |
d3f6bad3 | 858 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
b668c9cf | 859 | { |
1304afb2 | 860 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b668c9cf PM |
861 | } |
862 | ||
863 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
864 | ||
f41d911f PM |
865 | #ifdef CONFIG_RCU_CPU_STALL_DETECTOR |
866 | ||
1ed509a2 PM |
867 | /* |
868 | * Because preemptable RCU does not exist, we never have to check for | |
869 | * tasks blocked within RCU read-side critical sections. | |
870 | */ | |
871 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
872 | { | |
873 | } | |
874 | ||
f41d911f PM |
875 | /* |
876 | * Because preemptable RCU does not exist, we never have to check for | |
877 | * tasks blocked within RCU read-side critical sections. | |
878 | */ | |
879 | static void rcu_print_task_stall(struct rcu_node *rnp) | |
880 | { | |
881 | } | |
882 | ||
53d84e00 PM |
883 | /* |
884 | * Because preemptible RCU does not exist, there is no need to suppress | |
885 | * its CPU stall warnings. | |
886 | */ | |
887 | static void rcu_preempt_stall_reset(void) | |
888 | { | |
889 | } | |
890 | ||
f41d911f PM |
891 | #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ |
892 | ||
b0e165c0 PM |
893 | /* |
894 | * Because there is no preemptable RCU, there can be no readers blocked, | |
49e29126 PM |
895 | * so there is no need to check for blocked tasks. So check only for |
896 | * bogus qsmask values. | |
b0e165c0 PM |
897 | */ |
898 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
899 | { | |
49e29126 | 900 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
901 | } |
902 | ||
33f76148 PM |
903 | #ifdef CONFIG_HOTPLUG_CPU |
904 | ||
dd5d19ba PM |
905 | /* |
906 | * Because preemptable RCU does not exist, it never needs to migrate | |
237c80c5 PM |
907 | * tasks that were blocked within RCU read-side critical sections, and |
908 | * such non-existent tasks cannot possibly have been blocking the current | |
909 | * grace period. | |
dd5d19ba | 910 | */ |
237c80c5 PM |
911 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
912 | struct rcu_node *rnp, | |
913 | struct rcu_data *rdp) | |
dd5d19ba | 914 | { |
237c80c5 | 915 | return 0; |
dd5d19ba PM |
916 | } |
917 | ||
33f76148 PM |
918 | /* |
919 | * Because preemptable RCU does not exist, it never needs CPU-offline | |
920 | * processing. | |
921 | */ | |
922 | static void rcu_preempt_offline_cpu(int cpu) | |
923 | { | |
924 | } | |
925 | ||
926 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
927 | ||
f41d911f PM |
928 | /* |
929 | * Because preemptable RCU does not exist, it never has any callbacks | |
930 | * to check. | |
931 | */ | |
1eba8f84 | 932 | static void rcu_preempt_check_callbacks(int cpu) |
f41d911f PM |
933 | { |
934 | } | |
935 | ||
936 | /* | |
937 | * Because preemptable RCU does not exist, it never has any callbacks | |
938 | * to process. | |
939 | */ | |
1eba8f84 | 940 | static void rcu_preempt_process_callbacks(void) |
f41d911f PM |
941 | { |
942 | } | |
943 | ||
019129d5 PM |
944 | /* |
945 | * Wait for an rcu-preempt grace period, but make it happen quickly. | |
946 | * But because preemptable RCU does not exist, map to rcu-sched. | |
947 | */ | |
948 | void synchronize_rcu_expedited(void) | |
949 | { | |
950 | synchronize_sched_expedited(); | |
951 | } | |
952 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
953 | ||
d9a3da06 PM |
954 | #ifdef CONFIG_HOTPLUG_CPU |
955 | ||
956 | /* | |
957 | * Because preemptable RCU does not exist, there is never any need to | |
958 | * report on tasks preempted in RCU read-side critical sections during | |
959 | * expedited RCU grace periods. | |
960 | */ | |
961 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) | |
962 | { | |
963 | return; | |
964 | } | |
965 | ||
966 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
967 | ||
f41d911f PM |
968 | /* |
969 | * Because preemptable RCU does not exist, it never has any work to do. | |
970 | */ | |
971 | static int rcu_preempt_pending(int cpu) | |
972 | { | |
973 | return 0; | |
974 | } | |
975 | ||
976 | /* | |
977 | * Because preemptable RCU does not exist, it never needs any CPU. | |
978 | */ | |
979 | static int rcu_preempt_needs_cpu(int cpu) | |
980 | { | |
981 | return 0; | |
982 | } | |
983 | ||
e74f4c45 PM |
984 | /* |
985 | * Because preemptable RCU does not exist, rcu_barrier() is just | |
986 | * another name for rcu_barrier_sched(). | |
987 | */ | |
988 | void rcu_barrier(void) | |
989 | { | |
990 | rcu_barrier_sched(); | |
991 | } | |
992 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
993 | ||
f41d911f PM |
994 | /* |
995 | * Because preemptable RCU does not exist, there is no per-CPU | |
996 | * data to initialize. | |
997 | */ | |
998 | static void __cpuinit rcu_preempt_init_percpu_data(int cpu) | |
999 | { | |
1000 | } | |
1001 | ||
e74f4c45 PM |
1002 | /* |
1003 | * Because there is no preemptable RCU, there are no callbacks to move. | |
1004 | */ | |
29494be7 | 1005 | static void rcu_preempt_send_cbs_to_online(void) |
e74f4c45 PM |
1006 | { |
1007 | } | |
1008 | ||
1eba8f84 PM |
1009 | /* |
1010 | * Because preemptable RCU does not exist, it need not be initialized. | |
1011 | */ | |
1012 | static void __init __rcu_init_preempt(void) | |
1013 | { | |
1014 | } | |
1015 | ||
f41d911f | 1016 | #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ |
8bd93a2c | 1017 | |
7b27d547 LJ |
1018 | #ifndef CONFIG_SMP |
1019 | ||
1020 | void synchronize_sched_expedited(void) | |
1021 | { | |
1022 | cond_resched(); | |
1023 | } | |
1024 | EXPORT_SYMBOL_GPL(synchronize_sched_expedited); | |
1025 | ||
1026 | #else /* #ifndef CONFIG_SMP */ | |
1027 | ||
e27fc964 TH |
1028 | static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0); |
1029 | static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0); | |
7b27d547 LJ |
1030 | |
1031 | static int synchronize_sched_expedited_cpu_stop(void *data) | |
1032 | { | |
1033 | /* | |
1034 | * There must be a full memory barrier on each affected CPU | |
1035 | * between the time that try_stop_cpus() is called and the | |
1036 | * time that it returns. | |
1037 | * | |
1038 | * In the current initial implementation of cpu_stop, the | |
1039 | * above condition is already met when the control reaches | |
1040 | * this point and the following smp_mb() is not strictly | |
1041 | * necessary. Do smp_mb() anyway for documentation and | |
1042 | * robustness against future implementation changes. | |
1043 | */ | |
1044 | smp_mb(); /* See above comment block. */ | |
1045 | return 0; | |
1046 | } | |
1047 | ||
1048 | /* | |
1049 | * Wait for an rcu-sched grace period to elapse, but use "big hammer" | |
1050 | * approach to force grace period to end quickly. This consumes | |
1051 | * significant time on all CPUs, and is thus not recommended for | |
1052 | * any sort of common-case code. | |
1053 | * | |
1054 | * Note that it is illegal to call this function while holding any | |
1055 | * lock that is acquired by a CPU-hotplug notifier. Failing to | |
1056 | * observe this restriction will result in deadlock. | |
db3a8920 | 1057 | * |
e27fc964 TH |
1058 | * This implementation can be thought of as an application of ticket |
1059 | * locking to RCU, with sync_sched_expedited_started and | |
1060 | * sync_sched_expedited_done taking on the roles of the halves | |
1061 | * of the ticket-lock word. Each task atomically increments | |
1062 | * sync_sched_expedited_started upon entry, snapshotting the old value, | |
1063 | * then attempts to stop all the CPUs. If this succeeds, then each | |
1064 | * CPU will have executed a context switch, resulting in an RCU-sched | |
1065 | * grace period. We are then done, so we use atomic_cmpxchg() to | |
1066 | * update sync_sched_expedited_done to match our snapshot -- but | |
1067 | * only if someone else has not already advanced past our snapshot. | |
1068 | * | |
1069 | * On the other hand, if try_stop_cpus() fails, we check the value | |
1070 | * of sync_sched_expedited_done. If it has advanced past our | |
1071 | * initial snapshot, then someone else must have forced a grace period | |
1072 | * some time after we took our snapshot. In this case, our work is | |
1073 | * done for us, and we can simply return. Otherwise, we try again, | |
1074 | * but keep our initial snapshot for purposes of checking for someone | |
1075 | * doing our work for us. | |
1076 | * | |
1077 | * If we fail too many times in a row, we fall back to synchronize_sched(). | |
7b27d547 LJ |
1078 | */ |
1079 | void synchronize_sched_expedited(void) | |
1080 | { | |
e27fc964 | 1081 | int firstsnap, s, snap, trycount = 0; |
7b27d547 | 1082 | |
e27fc964 TH |
1083 | /* Note that atomic_inc_return() implies full memory barrier. */ |
1084 | firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started); | |
7b27d547 | 1085 | get_online_cpus(); |
e27fc964 TH |
1086 | |
1087 | /* | |
1088 | * Each pass through the following loop attempts to force a | |
1089 | * context switch on each CPU. | |
1090 | */ | |
7b27d547 LJ |
1091 | while (try_stop_cpus(cpu_online_mask, |
1092 | synchronize_sched_expedited_cpu_stop, | |
1093 | NULL) == -EAGAIN) { | |
1094 | put_online_cpus(); | |
e27fc964 TH |
1095 | |
1096 | /* No joy, try again later. Or just synchronize_sched(). */ | |
7b27d547 LJ |
1097 | if (trycount++ < 10) |
1098 | udelay(trycount * num_online_cpus()); | |
1099 | else { | |
1100 | synchronize_sched(); | |
1101 | return; | |
1102 | } | |
e27fc964 TH |
1103 | |
1104 | /* Check to see if someone else did our work for us. */ | |
1105 | s = atomic_read(&sync_sched_expedited_done); | |
1106 | if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) { | |
7b27d547 LJ |
1107 | smp_mb(); /* ensure test happens before caller kfree */ |
1108 | return; | |
1109 | } | |
e27fc964 TH |
1110 | |
1111 | /* | |
1112 | * Refetching sync_sched_expedited_started allows later | |
1113 | * callers to piggyback on our grace period. We subtract | |
1114 | * 1 to get the same token that the last incrementer got. | |
1115 | * We retry after they started, so our grace period works | |
1116 | * for them, and they started after our first try, so their | |
1117 | * grace period works for us. | |
1118 | */ | |
7b27d547 | 1119 | get_online_cpus(); |
e27fc964 TH |
1120 | snap = atomic_read(&sync_sched_expedited_started) - 1; |
1121 | smp_mb(); /* ensure read is before try_stop_cpus(). */ | |
7b27d547 | 1122 | } |
e27fc964 TH |
1123 | |
1124 | /* | |
1125 | * Everyone up to our most recent fetch is covered by our grace | |
1126 | * period. Update the counter, but only if our work is still | |
1127 | * relevant -- which it won't be if someone who started later | |
1128 | * than we did beat us to the punch. | |
1129 | */ | |
1130 | do { | |
1131 | s = atomic_read(&sync_sched_expedited_done); | |
1132 | if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) { | |
1133 | smp_mb(); /* ensure test happens before caller kfree */ | |
1134 | break; | |
1135 | } | |
1136 | } while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s); | |
1137 | ||
7b27d547 LJ |
1138 | put_online_cpus(); |
1139 | } | |
1140 | EXPORT_SYMBOL_GPL(synchronize_sched_expedited); | |
1141 | ||
1142 | #endif /* #else #ifndef CONFIG_SMP */ | |
1143 | ||
8bd93a2c PM |
1144 | #if !defined(CONFIG_RCU_FAST_NO_HZ) |
1145 | ||
1146 | /* | |
1147 | * Check to see if any future RCU-related work will need to be done | |
1148 | * by the current CPU, even if none need be done immediately, returning | |
1149 | * 1 if so. This function is part of the RCU implementation; it is -not- | |
1150 | * an exported member of the RCU API. | |
1151 | * | |
1152 | * Because we have preemptible RCU, just check whether this CPU needs | |
1153 | * any flavor of RCU. Do not chew up lots of CPU cycles with preemption | |
1154 | * disabled in a most-likely vain attempt to cause RCU not to need this CPU. | |
1155 | */ | |
1156 | int rcu_needs_cpu(int cpu) | |
1157 | { | |
1158 | return rcu_needs_cpu_quick_check(cpu); | |
1159 | } | |
1160 | ||
a47cd880 PM |
1161 | /* |
1162 | * Check to see if we need to continue a callback-flush operations to | |
1163 | * allow the last CPU to enter dyntick-idle mode. But fast dyntick-idle | |
1164 | * entry is not configured, so we never do need to. | |
1165 | */ | |
1166 | static void rcu_needs_cpu_flush(void) | |
1167 | { | |
1168 | } | |
1169 | ||
8bd93a2c PM |
1170 | #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
1171 | ||
1172 | #define RCU_NEEDS_CPU_FLUSHES 5 | |
a47cd880 | 1173 | static DEFINE_PER_CPU(int, rcu_dyntick_drain); |
71da8132 | 1174 | static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff); |
8bd93a2c PM |
1175 | |
1176 | /* | |
1177 | * Check to see if any future RCU-related work will need to be done | |
1178 | * by the current CPU, even if none need be done immediately, returning | |
1179 | * 1 if so. This function is part of the RCU implementation; it is -not- | |
1180 | * an exported member of the RCU API. | |
1181 | * | |
1182 | * Because we are not supporting preemptible RCU, attempt to accelerate | |
1183 | * any current grace periods so that RCU no longer needs this CPU, but | |
1184 | * only if all other CPUs are already in dynticks-idle mode. This will | |
1185 | * allow the CPU cores to be powered down immediately, as opposed to after | |
1186 | * waiting many milliseconds for grace periods to elapse. | |
a47cd880 PM |
1187 | * |
1188 | * Because it is not legal to invoke rcu_process_callbacks() with irqs | |
1189 | * disabled, we do one pass of force_quiescent_state(), then do a | |
1190 | * raise_softirq() to cause rcu_process_callbacks() to be invoked later. | |
1191 | * The per-cpu rcu_dyntick_drain variable controls the sequencing. | |
8bd93a2c PM |
1192 | */ |
1193 | int rcu_needs_cpu(int cpu) | |
1194 | { | |
a47cd880 | 1195 | int c = 0; |
77e38ed3 PM |
1196 | int snap; |
1197 | int snap_nmi; | |
8bd93a2c PM |
1198 | int thatcpu; |
1199 | ||
622ea685 PM |
1200 | /* Check for being in the holdoff period. */ |
1201 | if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies) | |
1202 | return rcu_needs_cpu_quick_check(cpu); | |
1203 | ||
8bd93a2c | 1204 | /* Don't bother unless we are the last non-dyntick-idle CPU. */ |
77e38ed3 PM |
1205 | for_each_online_cpu(thatcpu) { |
1206 | if (thatcpu == cpu) | |
1207 | continue; | |
d822ed10 PM |
1208 | snap = per_cpu(rcu_dynticks, thatcpu).dynticks; |
1209 | snap_nmi = per_cpu(rcu_dynticks, thatcpu).dynticks_nmi; | |
77e38ed3 PM |
1210 | smp_mb(); /* Order sampling of snap with end of grace period. */ |
1211 | if (((snap & 0x1) != 0) || ((snap_nmi & 0x1) != 0)) { | |
a47cd880 | 1212 | per_cpu(rcu_dyntick_drain, cpu) = 0; |
71da8132 | 1213 | per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1; |
8bd93a2c | 1214 | return rcu_needs_cpu_quick_check(cpu); |
8bd93a2c | 1215 | } |
77e38ed3 | 1216 | } |
a47cd880 PM |
1217 | |
1218 | /* Check and update the rcu_dyntick_drain sequencing. */ | |
1219 | if (per_cpu(rcu_dyntick_drain, cpu) <= 0) { | |
1220 | /* First time through, initialize the counter. */ | |
1221 | per_cpu(rcu_dyntick_drain, cpu) = RCU_NEEDS_CPU_FLUSHES; | |
1222 | } else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) { | |
1223 | /* We have hit the limit, so time to give up. */ | |
71da8132 | 1224 | per_cpu(rcu_dyntick_holdoff, cpu) = jiffies; |
a47cd880 PM |
1225 | return rcu_needs_cpu_quick_check(cpu); |
1226 | } | |
1227 | ||
1228 | /* Do one step pushing remaining RCU callbacks through. */ | |
1229 | if (per_cpu(rcu_sched_data, cpu).nxtlist) { | |
1230 | rcu_sched_qs(cpu); | |
1231 | force_quiescent_state(&rcu_sched_state, 0); | |
1232 | c = c || per_cpu(rcu_sched_data, cpu).nxtlist; | |
1233 | } | |
1234 | if (per_cpu(rcu_bh_data, cpu).nxtlist) { | |
1235 | rcu_bh_qs(cpu); | |
1236 | force_quiescent_state(&rcu_bh_state, 0); | |
1237 | c = c || per_cpu(rcu_bh_data, cpu).nxtlist; | |
8bd93a2c PM |
1238 | } |
1239 | ||
1240 | /* If RCU callbacks are still pending, RCU still needs this CPU. */ | |
622ea685 | 1241 | if (c) |
a47cd880 | 1242 | raise_softirq(RCU_SOFTIRQ); |
8bd93a2c PM |
1243 | return c; |
1244 | } | |
1245 | ||
a47cd880 PM |
1246 | /* |
1247 | * Check to see if we need to continue a callback-flush operations to | |
1248 | * allow the last CPU to enter dyntick-idle mode. | |
1249 | */ | |
1250 | static void rcu_needs_cpu_flush(void) | |
1251 | { | |
1252 | int cpu = smp_processor_id(); | |
71da8132 | 1253 | unsigned long flags; |
a47cd880 PM |
1254 | |
1255 | if (per_cpu(rcu_dyntick_drain, cpu) <= 0) | |
1256 | return; | |
71da8132 | 1257 | local_irq_save(flags); |
a47cd880 | 1258 | (void)rcu_needs_cpu(cpu); |
71da8132 | 1259 | local_irq_restore(flags); |
a47cd880 PM |
1260 | } |
1261 | ||
8bd93a2c | 1262 | #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |