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1 : : /* SPDX-License-Identifier: GPL-2.0+ */
2 : : /*
3 : : * RCU expedited grace periods
4 : : *
5 : : * Copyright IBM Corporation, 2016
6 : : *
7 : : * Authors: Paul E. McKenney <paulmck@linux.ibm.com>
8 : : */
9 : :
10 : : #include <linux/lockdep.h>
11 : :
12 : : static void rcu_exp_handler(void *unused);
13 : : static int rcu_print_task_exp_stall(struct rcu_node *rnp);
14 : :
15 : : /*
16 : : * Record the start of an expedited grace period.
17 : : */
18 : : static void rcu_exp_gp_seq_start(void)
19 : : {
20 : 5656 : rcu_seq_start(&rcu_state.expedited_sequence);
21 : : }
22 : :
23 : : /*
24 : : * Return then value that expedited-grace-period counter will have
25 : : * at the end of the current grace period.
26 : : */
27 : : static __maybe_unused unsigned long rcu_exp_gp_seq_endval(void)
28 : : {
29 : : return rcu_seq_endval(&rcu_state.expedited_sequence);
30 : : }
31 : :
32 : : /*
33 : : * Record the end of an expedited grace period.
34 : : */
35 : : static void rcu_exp_gp_seq_end(void)
36 : : {
37 : 5656 : rcu_seq_end(&rcu_state.expedited_sequence);
38 : 5656 : smp_mb(); /* Ensure that consecutive grace periods serialize. */
39 : : }
40 : :
41 : : /*
42 : : * Take a snapshot of the expedited-grace-period counter.
43 : : */
44 : : static unsigned long rcu_exp_gp_seq_snap(void)
45 : : {
46 : : unsigned long s;
47 : :
48 : 5656 : smp_mb(); /* Caller's modifications seen first by other CPUs. */
49 : : s = rcu_seq_snap(&rcu_state.expedited_sequence);
50 : : trace_rcu_exp_grace_period(rcu_state.name, s, TPS("snap"));
51 : : return s;
52 : : }
53 : :
54 : : /*
55 : : * Given a counter snapshot from rcu_exp_gp_seq_snap(), return true
56 : : * if a full expedited grace period has elapsed since that snapshot
57 : : * was taken.
58 : : */
59 : : static bool rcu_exp_gp_seq_done(unsigned long s)
60 : : {
61 : : return rcu_seq_done(&rcu_state.expedited_sequence, s);
62 : : }
63 : :
64 : : /*
65 : : * Reset the ->expmaskinit values in the rcu_node tree to reflect any
66 : : * recent CPU-online activity. Note that these masks are not cleared
67 : : * when CPUs go offline, so they reflect the union of all CPUs that have
68 : : * ever been online. This means that this function normally takes its
69 : : * no-work-to-do fastpath.
70 : : */
71 : 5656 : static void sync_exp_reset_tree_hotplug(void)
72 : : {
73 : : bool done;
74 : : unsigned long flags;
75 : : unsigned long mask;
76 : : unsigned long oldmask;
77 : 5656 : int ncpus = smp_load_acquire(&rcu_state.ncpus); /* Order vs. locking. */
78 : : struct rcu_node *rnp;
79 : : struct rcu_node *rnp_up;
80 : :
81 : : /* If no new CPUs onlined since last time, nothing to do. */
82 [ + + ]: 5656 : if (likely(ncpus == rcu_state.ncpus_snap))
83 : 5656 : return;
84 : 404 : rcu_state.ncpus_snap = ncpus;
85 : :
86 : : /*
87 : : * Each pass through the following loop propagates newly onlined
88 : : * CPUs for the current rcu_node structure up the rcu_node tree.
89 : : */
90 [ + + ]: 808 : rcu_for_each_leaf_node(rnp) {
91 : 404 : raw_spin_lock_irqsave_rcu_node(rnp, flags);
92 [ - + ]: 404 : if (rnp->expmaskinit == rnp->expmaskinitnext) {
93 : 0 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
94 : 0 : continue; /* No new CPUs, nothing to do. */
95 : : }
96 : :
97 : : /* Update this node's mask, track old value for propagation. */
98 : : oldmask = rnp->expmaskinit;
99 : 404 : rnp->expmaskinit = rnp->expmaskinitnext;
100 : 404 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
101 : :
102 : : /* If was already nonzero, nothing to propagate. */
103 [ - + ]: 404 : if (oldmask)
104 : 0 : continue;
105 : :
106 : : /* Propagate the new CPU up the tree. */
107 : 404 : mask = rnp->grpmask;
108 : 404 : rnp_up = rnp->parent;
109 : : done = false;
110 [ - + ]: 808 : while (rnp_up) {
111 : 0 : raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
112 [ # # ]: 0 : if (rnp_up->expmaskinit)
113 : : done = true;
114 : 0 : rnp_up->expmaskinit |= mask;
115 : 0 : raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
116 [ # # ]: 0 : if (done)
117 : : break;
118 : 0 : mask = rnp_up->grpmask;
119 : 0 : rnp_up = rnp_up->parent;
120 : : }
121 : : }
122 : : }
123 : :
124 : : /*
125 : : * Reset the ->expmask values in the rcu_node tree in preparation for
126 : : * a new expedited grace period.
127 : : */
128 : 5656 : static void __maybe_unused sync_exp_reset_tree(void)
129 : : {
130 : : unsigned long flags;
131 : : struct rcu_node *rnp;
132 : :
133 : 5656 : sync_exp_reset_tree_hotplug();
134 [ + + ]: 11312 : rcu_for_each_node_breadth_first(rnp) {
135 : 5656 : raw_spin_lock_irqsave_rcu_node(rnp, flags);
136 [ - + # # ]: 5656 : WARN_ON_ONCE(rnp->expmask);
137 : 5656 : WRITE_ONCE(rnp->expmask, rnp->expmaskinit);
138 : 5656 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
139 : : }
140 : 5656 : }
141 : :
142 : : /*
143 : : * Return non-zero if there is no RCU expedited grace period in progress
144 : : * for the specified rcu_node structure, in other words, if all CPUs and
145 : : * tasks covered by the specified rcu_node structure have done their bit
146 : : * for the current expedited grace period. Works only for preemptible
147 : : * RCU -- other RCU implementation use other means.
148 : : *
149 : : * Caller must hold the specificed rcu_node structure's ->lock
150 : : */
151 : : static bool sync_rcu_preempt_exp_done(struct rcu_node *rnp)
152 : : {
153 : : raw_lockdep_assert_held_rcu_node(rnp);
154 : :
155 [ + - + + : 36308 : return rnp->exp_tasks == NULL &&
+ - + + ]
156 : : READ_ONCE(rnp->expmask) == 0;
157 : : }
158 : :
159 : : /*
160 : : * Like sync_rcu_preempt_exp_done(), but this function assumes the caller
161 : : * doesn't hold the rcu_node's ->lock, and will acquire and release the lock
162 : : * itself
163 : : */
164 : 8984 : static bool sync_rcu_preempt_exp_done_unlocked(struct rcu_node *rnp)
165 : : {
166 : : unsigned long flags;
167 : : bool ret;
168 : :
169 : 8984 : raw_spin_lock_irqsave_rcu_node(rnp, flags);
170 : : ret = sync_rcu_preempt_exp_done(rnp);
171 : 8984 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
172 : :
173 : 8984 : return ret;
174 : : }
175 : :
176 : :
177 : : /*
178 : : * Report the exit from RCU read-side critical section for the last task
179 : : * that queued itself during or before the current expedited preemptible-RCU
180 : : * grace period. This event is reported either to the rcu_node structure on
181 : : * which the task was queued or to one of that rcu_node structure's ancestors,
182 : : * recursively up the tree. (Calm down, calm down, we do the recursion
183 : : * iteratively!)
184 : : *
185 : : * Caller must hold the specified rcu_node structure's ->lock.
186 : : */
187 : 9170 : static void __rcu_report_exp_rnp(struct rcu_node *rnp,
188 : : bool wake, unsigned long flags)
189 : : __releases(rnp->lock)
190 : : {
191 : : unsigned long mask;
192 : :
193 : : for (;;) {
194 [ + + ]: 9170 : if (!sync_rcu_preempt_exp_done(rnp)) {
195 [ - + ]: 3514 : if (!rnp->expmask)
196 : : rcu_initiate_boost(rnp, flags);
197 : : else
198 : 3514 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
199 : : break;
200 : : }
201 [ + - ]: 5656 : if (rnp->parent == NULL) {
202 : 5656 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
203 [ + + ]: 5656 : if (wake) {
204 : 1760 : smp_mb(); /* EGP done before wake_up(). */
205 : 1760 : swake_up_one(&rcu_state.expedited_wq);
206 : : }
207 : : break;
208 : : }
209 : 0 : mask = rnp->grpmask;
210 : : raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
211 : 0 : rnp = rnp->parent;
212 : 0 : raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
213 [ # # # # ]: 0 : WARN_ON_ONCE(!(rnp->expmask & mask));
214 : 0 : WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
215 : : }
216 : 9170 : }
217 : :
218 : : /*
219 : : * Report expedited quiescent state for specified node. This is a
220 : : * lock-acquisition wrapper function for __rcu_report_exp_rnp().
221 : : */
222 : : static void __maybe_unused rcu_report_exp_rnp(struct rcu_node *rnp, bool wake)
223 : : {
224 : : unsigned long flags;
225 : :
226 : : raw_spin_lock_irqsave_rcu_node(rnp, flags);
227 : : __rcu_report_exp_rnp(rnp, wake, flags);
228 : : }
229 : :
230 : : /*
231 : : * Report expedited quiescent state for multiple CPUs, all covered by the
232 : : * specified leaf rcu_node structure.
233 : : */
234 : 9166 : static void rcu_report_exp_cpu_mult(struct rcu_node *rnp,
235 : : unsigned long mask, bool wake)
236 : : {
237 : : unsigned long flags;
238 : :
239 : 9166 : raw_spin_lock_irqsave_rcu_node(rnp, flags);
240 [ - + ]: 9170 : if (!(rnp->expmask & mask)) {
241 : 0 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
242 : 9166 : return;
243 : : }
244 : 9170 : WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
245 : 9170 : __rcu_report_exp_rnp(rnp, wake, flags); /* Releases rnp->lock. */
246 : : }
247 : :
248 : : /*
249 : : * Report expedited quiescent state for specified rcu_data (CPU).
250 : : */
251 : : static void rcu_report_exp_rdp(struct rcu_data *rdp)
252 : : {
253 : : WRITE_ONCE(rdp->exp_deferred_qs, false);
254 : 3514 : rcu_report_exp_cpu_mult(rdp->mynode, rdp->grpmask, true);
255 : : }
256 : :
257 : : /* Common code for work-done checking. */
258 : : static bool sync_exp_work_done(unsigned long s)
259 : : {
260 [ + + + + : 13796 : if (rcu_exp_gp_seq_done(s)) {
# # # # #
# - + ]
261 : : trace_rcu_exp_grace_period(rcu_state.name, s, TPS("done"));
262 : 5656 : smp_mb(); /* Ensure test happens before caller kfree(). */
263 : : return true;
264 : : }
265 : : return false;
266 : : }
267 : :
268 : : /*
269 : : * Funnel-lock acquisition for expedited grace periods. Returns true
270 : : * if some other task completed an expedited grace period that this task
271 : : * can piggy-back on, and with no mutex held. Otherwise, returns false
272 : : * with the mutex held, indicating that the caller must actually do the
273 : : * expedited grace period.
274 : : */
275 : 5656 : static bool exp_funnel_lock(unsigned long s)
276 : : {
277 : 11312 : struct rcu_data *rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
278 : 5656 : struct rcu_node *rnp = rdp->mynode;
279 : : struct rcu_node *rnp_root = rcu_get_root();
280 : :
281 : : /* Low-contention fastpath. */
282 [ + - - + ]: 5656 : if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&
283 [ # # ]: 0 : (rnp == rnp_root ||
284 [ - + ]: 5656 : ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&
285 : 5656 : mutex_trylock(&rcu_state.exp_mutex))
286 : : goto fastpath;
287 : :
288 : : /*
289 : : * Each pass through the following loop works its way up
290 : : * the rcu_node tree, returning if others have done the work or
291 : : * otherwise falls through to acquire ->exp_mutex. The mapping
292 : : * from CPU to rcu_node structure can be inexact, as it is just
293 : : * promoting locality and is not strictly needed for correctness.
294 : : */
295 [ # # ]: 0 : for (; rnp != NULL; rnp = rnp->parent) {
296 [ # # ]: 0 : if (sync_exp_work_done(s))
297 : : return true;
298 : :
299 : : /* Work not done, either wait here or go up. */
300 : : spin_lock(&rnp->exp_lock);
301 [ # # ]: 0 : if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {
302 : :
303 : : /* Someone else doing GP, so wait for them. */
304 : : spin_unlock(&rnp->exp_lock);
305 : : trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
306 : : rnp->grplo, rnp->grphi,
307 : : TPS("wait"));
308 [ # # # # ]: 0 : wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
309 : : sync_exp_work_done(s));
310 : : return true;
311 : : }
312 : 0 : rnp->exp_seq_rq = s; /* Followers can wait on us. */
313 : : spin_unlock(&rnp->exp_lock);
314 : : trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
315 : : rnp->grplo, rnp->grphi, TPS("nxtlvl"));
316 : : }
317 : 0 : mutex_lock(&rcu_state.exp_mutex);
318 : : fastpath:
319 [ - + ]: 5656 : if (sync_exp_work_done(s)) {
320 : 0 : mutex_unlock(&rcu_state.exp_mutex);
321 : 0 : return true;
322 : : }
323 : : rcu_exp_gp_seq_start();
324 : : trace_rcu_exp_grace_period(rcu_state.name, s, TPS("start"));
325 : 5656 : return false;
326 : : }
327 : :
328 : : /*
329 : : * Select the CPUs within the specified rcu_node that the upcoming
330 : : * expedited grace period needs to wait for.
331 : : */
332 : 5656 : static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
333 : : {
334 : : int cpu;
335 : : unsigned long flags;
336 : : unsigned long mask_ofl_test;
337 : : unsigned long mask_ofl_ipi;
338 : : int ret;
339 : : struct rcu_exp_work *rewp =
340 : : container_of(wp, struct rcu_exp_work, rew_work);
341 : 5656 : struct rcu_node *rnp = container_of(rewp, struct rcu_node, rew);
342 : :
343 : 5656 : raw_spin_lock_irqsave_rcu_node(rnp, flags);
344 : :
345 : : /* Each pass checks a CPU for identity, offline, and idle. */
346 : : mask_ofl_test = 0;
347 [ + + ]: 28280 : for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) {
348 : 22624 : unsigned long mask = leaf_node_cpu_bit(rnp, cpu);
349 : 22624 : struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
350 : : int snap;
351 : :
352 [ + + - + ]: 39592 : if (raw_smp_processor_id() == cpu ||
353 : 16968 : !(rnp->qsmaskinitnext & mask)) {
354 : 5656 : mask_ofl_test |= mask;
355 : : } else {
356 : 16968 : snap = rcu_dynticks_snap(rdp);
357 [ + + ]: 16968 : if (rcu_dynticks_in_eqs(snap))
358 : 13388 : mask_ofl_test |= mask;
359 : : else
360 : 3580 : rdp->exp_dynticks_snap = snap;
361 : : }
362 : : }
363 : 5656 : mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
364 : :
365 : : /*
366 : : * Need to wait for any blocked tasks as well. Note that
367 : : * additional blocking tasks will also block the expedited GP
368 : : * until such time as the ->expmask bits are cleared.
369 : : */
370 : : if (rcu_preempt_has_tasks(rnp))
371 : : rnp->exp_tasks = rnp->blkd_tasks.next;
372 : 5656 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
373 : :
374 : : /* IPI the remaining CPUs for expedited quiescent state. */
375 [ + + ]: 9236 : for_each_leaf_node_cpu_mask(rnp, cpu, mask_ofl_ipi) {
376 : 3580 : unsigned long mask = leaf_node_cpu_bit(rnp, cpu);
377 : 3580 : struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
378 : :
379 : : retry_ipi:
380 [ + + ]: 7160 : if (rcu_dynticks_in_eqs_since(rdp, rdp->exp_dynticks_snap)) {
381 : 66 : mask_ofl_test |= mask;
382 : 66 : continue;
383 : : }
384 [ - + ]: 7028 : if (get_cpu() == cpu) {
385 : 0 : put_cpu();
386 : 0 : continue;
387 : : }
388 : 3514 : ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
389 : 3514 : put_cpu();
390 [ + - ]: 3514 : if (!ret) {
391 : 3514 : mask_ofl_ipi &= ~mask;
392 : 3514 : continue;
393 : : }
394 : : /* Failed, raced with CPU hotplug operation. */
395 : 0 : raw_spin_lock_irqsave_rcu_node(rnp, flags);
396 [ # # # # ]: 0 : if ((rnp->qsmaskinitnext & mask) &&
397 : 0 : (rnp->expmask & mask)) {
398 : : /* Online, so delay for a bit and try again. */
399 : 0 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
400 : : trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("selectofl"));
401 : 0 : schedule_timeout_uninterruptible(1);
402 : 0 : goto retry_ipi;
403 : : }
404 : : /* CPU really is offline, so we can ignore it. */
405 [ # # ]: 0 : if (!(rnp->expmask & mask))
406 : 0 : mask_ofl_ipi &= ~mask;
407 : 0 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
408 : : }
409 : : /* Report quiescent states for those that went offline. */
410 : 5656 : mask_ofl_test |= mask_ofl_ipi;
411 [ + - ]: 5656 : if (mask_ofl_test)
412 : 5656 : rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false);
413 : 5656 : }
414 : :
415 : : /*
416 : : * Select the nodes that the upcoming expedited grace period needs
417 : : * to wait for.
418 : : */
419 : 5656 : static void sync_rcu_exp_select_cpus(void)
420 : : {
421 : : int cpu;
422 : : struct rcu_node *rnp;
423 : :
424 : : trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("reset"));
425 : 5656 : sync_exp_reset_tree();
426 : : trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("select"));
427 : :
428 : : /* Schedule work for each leaf rcu_node structure. */
429 [ + + ]: 11312 : rcu_for_each_leaf_node(rnp) {
430 : 5656 : rnp->exp_need_flush = false;
431 [ - + ]: 5656 : if (!READ_ONCE(rnp->expmask))
432 : 0 : continue; /* Avoid early boot non-existent wq. */
433 [ + - + - ]: 11312 : if (!READ_ONCE(rcu_par_gp_wq) ||
434 [ + - ]: 11312 : rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
435 : 5656 : rcu_is_last_leaf_node(rnp)) {
436 : : /* No workqueues yet or last leaf, do direct call. */
437 : 5656 : sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work);
438 : 5656 : continue;
439 : : }
440 : 0 : INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
441 : 0 : cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
442 : : /* If all offline, queue the work on an unbound CPU. */
443 [ # # ]: 0 : if (unlikely(cpu > rnp->grphi - rnp->grplo))
444 : : cpu = WORK_CPU_UNBOUND;
445 : : else
446 : 0 : cpu += rnp->grplo;
447 : 0 : queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
448 : 0 : rnp->exp_need_flush = true;
449 : : }
450 : :
451 : : /* Wait for workqueue jobs (if any) to complete. */
452 [ + + ]: 11312 : rcu_for_each_leaf_node(rnp)
453 [ - + ]: 5656 : if (rnp->exp_need_flush)
454 : 0 : flush_work(&rnp->rew.rew_work);
455 : 5656 : }
456 : :
457 : 5656 : static void synchronize_sched_expedited_wait(void)
458 : : {
459 : : int cpu;
460 : : unsigned long jiffies_stall;
461 : : unsigned long jiffies_start;
462 : : unsigned long mask;
463 : : int ndetected;
464 : : struct rcu_node *rnp;
465 : : struct rcu_node *rnp_root = rcu_get_root();
466 : : int ret;
467 : :
468 : : trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait"));
469 : 5656 : jiffies_stall = rcu_jiffies_till_stall_check();
470 : 5656 : jiffies_start = jiffies;
471 : :
472 : : for (;;) {
473 [ - + + + : 8984 : ret = swait_event_timeout_exclusive(
- + + + ]
474 : : rcu_state.expedited_wq,
475 : : sync_rcu_preempt_exp_done_unlocked(rnp_root),
476 : : jiffies_stall);
477 [ - + # # ]: 5656 : if (ret > 0 || sync_rcu_preempt_exp_done_unlocked(rnp_root))
478 : 5656 : return;
479 [ # # ]: 0 : WARN_ON(ret < 0); /* workqueues should not be signaled. */
480 [ # # ]: 0 : if (rcu_cpu_stall_suppress)
481 : 0 : continue;
482 : : panic_on_rcu_stall();
483 : 0 : pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
484 : : rcu_state.name);
485 : : ndetected = 0;
486 [ # # ]: 0 : rcu_for_each_leaf_node(rnp) {
487 : : ndetected += rcu_print_task_exp_stall(rnp);
488 [ # # ]: 0 : for_each_leaf_node_possible_cpu(rnp, cpu) {
489 : : struct rcu_data *rdp;
490 : :
491 : 0 : mask = leaf_node_cpu_bit(rnp, cpu);
492 [ # # ]: 0 : if (!(READ_ONCE(rnp->expmask) & mask))
493 : 0 : continue;
494 : 0 : ndetected++;
495 : 0 : rdp = per_cpu_ptr(&rcu_data, cpu);
496 : 0 : pr_cont(" %d-%c%c%c", cpu,
497 : : "O."[!!cpu_online(cpu)],
498 : : "o."[!!(rdp->grpmask & rnp->expmaskinit)],
499 : : "N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
500 : : }
501 : : }
502 : 0 : pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
503 : : jiffies - jiffies_start, rcu_state.expedited_sequence,
504 : : READ_ONCE(rnp_root->expmask),
505 : : ".T"[!!rnp_root->exp_tasks]);
506 [ # # ]: 0 : if (ndetected) {
507 : 0 : pr_err("blocking rcu_node structures:");
508 [ # # ]: 0 : rcu_for_each_node_breadth_first(rnp) {
509 [ # # ]: 0 : if (rnp == rnp_root)
510 : 0 : continue; /* printed unconditionally */
511 [ # # ]: 0 : if (sync_rcu_preempt_exp_done_unlocked(rnp))
512 : 0 : continue;
513 : 0 : pr_cont(" l=%u:%d-%d:%#lx/%c",
514 : : rnp->level, rnp->grplo, rnp->grphi,
515 : : READ_ONCE(rnp->expmask),
516 : : ".T"[!!rnp->exp_tasks]);
517 : : }
518 : 0 : pr_cont("\n");
519 : : }
520 [ # # ]: 0 : rcu_for_each_leaf_node(rnp) {
521 [ # # ]: 0 : for_each_leaf_node_possible_cpu(rnp, cpu) {
522 : 0 : mask = leaf_node_cpu_bit(rnp, cpu);
523 [ # # ]: 0 : if (!(READ_ONCE(rnp->expmask) & mask))
524 : 0 : continue;
525 : 0 : dump_cpu_task(cpu);
526 : : }
527 : : }
528 : 0 : jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;
529 : : }
530 : : }
531 : :
532 : : /*
533 : : * Wait for the current expedited grace period to complete, and then
534 : : * wake up everyone who piggybacked on the just-completed expedited
535 : : * grace period. Also update all the ->exp_seq_rq counters as needed
536 : : * in order to avoid counter-wrap problems.
537 : : */
538 : 5656 : static void rcu_exp_wait_wake(unsigned long s)
539 : : {
540 : : struct rcu_node *rnp;
541 : :
542 : 5656 : synchronize_sched_expedited_wait();
543 : :
544 : : // Switch over to wakeup mode, allowing the next GP to proceed.
545 : : // End the previous grace period only after acquiring the mutex
546 : : // to ensure that only one GP runs concurrently with wakeups.
547 : 5656 : mutex_lock(&rcu_state.exp_wake_mutex);
548 : : rcu_exp_gp_seq_end();
549 : : trace_rcu_exp_grace_period(rcu_state.name, s, TPS("end"));
550 : :
551 [ + + ]: 11312 : rcu_for_each_node_breadth_first(rnp) {
552 [ + - ]: 5656 : if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {
553 : : spin_lock(&rnp->exp_lock);
554 : : /* Recheck, avoid hang in case someone just arrived. */
555 [ + - ]: 5656 : if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
556 : 5656 : rnp->exp_seq_rq = s;
557 : : spin_unlock(&rnp->exp_lock);
558 : : }
559 : 5656 : smp_mb(); /* All above changes before wakeup. */
560 : 5656 : wake_up_all(&rnp->exp_wq[rcu_seq_ctr(s) & 0x3]);
561 : : }
562 : : trace_rcu_exp_grace_period(rcu_state.name, s, TPS("endwake"));
563 : 5656 : mutex_unlock(&rcu_state.exp_wake_mutex);
564 : 5656 : }
565 : :
566 : : /*
567 : : * Common code to drive an expedited grace period forward, used by
568 : : * workqueues and mid-boot-time tasks.
569 : : */
570 : : static void rcu_exp_sel_wait_wake(unsigned long s)
571 : : {
572 : : /* Initialize the rcu_node tree in preparation for the wait. */
573 : 5656 : sync_rcu_exp_select_cpus();
574 : :
575 : : /* Wait and clean up, including waking everyone. */
576 : 5656 : rcu_exp_wait_wake(s);
577 : : }
578 : :
579 : : /*
580 : : * Work-queue handler to drive an expedited grace period forward.
581 : : */
582 : 5656 : static void wait_rcu_exp_gp(struct work_struct *wp)
583 : : {
584 : : struct rcu_exp_work *rewp;
585 : :
586 : : rewp = container_of(wp, struct rcu_exp_work, rew_work);
587 : 5656 : rcu_exp_sel_wait_wake(rewp->rew_s);
588 : 5656 : }
589 : :
590 : : #ifdef CONFIG_PREEMPT_RCU
591 : :
592 : : /*
593 : : * Remote handler for smp_call_function_single(). If there is an
594 : : * RCU read-side critical section in effect, request that the
595 : : * next rcu_read_unlock() record the quiescent state up the
596 : : * ->expmask fields in the rcu_node tree. Otherwise, immediately
597 : : * report the quiescent state.
598 : : */
599 : : static void rcu_exp_handler(void *unused)
600 : : {
601 : : unsigned long flags;
602 : : struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
603 : : struct rcu_node *rnp = rdp->mynode;
604 : : struct task_struct *t = current;
605 : :
606 : : /*
607 : : * First, the common case of not being in an RCU read-side
608 : : * critical section. If also enabled or idle, immediately
609 : : * report the quiescent state, otherwise defer.
610 : : */
611 : : if (!t->rcu_read_lock_nesting) {
612 : : if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) ||
613 : : rcu_dynticks_curr_cpu_in_eqs()) {
614 : : rcu_report_exp_rdp(rdp);
615 : : } else {
616 : : rdp->exp_deferred_qs = true;
617 : : set_tsk_need_resched(t);
618 : : set_preempt_need_resched();
619 : : }
620 : : return;
621 : : }
622 : :
623 : : /*
624 : : * Second, the less-common case of being in an RCU read-side
625 : : * critical section. In this case we can count on a future
626 : : * rcu_read_unlock(). However, this rcu_read_unlock() might
627 : : * execute on some other CPU, but in that case there will be
628 : : * a future context switch. Either way, if the expedited
629 : : * grace period is still waiting on this CPU, set ->deferred_qs
630 : : * so that the eventual quiescent state will be reported.
631 : : * Note that there is a large group of race conditions that
632 : : * can have caused this quiescent state to already have been
633 : : * reported, so we really do need to check ->expmask.
634 : : */
635 : : if (t->rcu_read_lock_nesting > 0) {
636 : : raw_spin_lock_irqsave_rcu_node(rnp, flags);
637 : : if (rnp->expmask & rdp->grpmask) {
638 : : rdp->exp_deferred_qs = true;
639 : : t->rcu_read_unlock_special.b.exp_hint = true;
640 : : }
641 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
642 : : return;
643 : : }
644 : :
645 : : /*
646 : : * The final and least likely case is where the interrupted
647 : : * code was just about to or just finished exiting the RCU-preempt
648 : : * read-side critical section, and no, we can't tell which.
649 : : * So either way, set ->deferred_qs to flag later code that
650 : : * a quiescent state is required.
651 : : *
652 : : * If the CPU is fully enabled (or if some buggy RCU-preempt
653 : : * read-side critical section is being used from idle), just
654 : : * invoke rcu_preempt_deferred_qs() to immediately report the
655 : : * quiescent state. We cannot use rcu_read_unlock_special()
656 : : * because we are in an interrupt handler, which will cause that
657 : : * function to take an early exit without doing anything.
658 : : *
659 : : * Otherwise, force a context switch after the CPU enables everything.
660 : : */
661 : : rdp->exp_deferred_qs = true;
662 : : if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) ||
663 : : WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs())) {
664 : : rcu_preempt_deferred_qs(t);
665 : : } else {
666 : : set_tsk_need_resched(t);
667 : : set_preempt_need_resched();
668 : : }
669 : : }
670 : :
671 : : /* PREEMPT=y, so no PREEMPT=n expedited grace period to clean up after. */
672 : : static void sync_sched_exp_online_cleanup(int cpu)
673 : : {
674 : : }
675 : :
676 : : /*
677 : : * Scan the current list of tasks blocked within RCU read-side critical
678 : : * sections, printing out the tid of each that is blocking the current
679 : : * expedited grace period.
680 : : */
681 : : static int rcu_print_task_exp_stall(struct rcu_node *rnp)
682 : : {
683 : : struct task_struct *t;
684 : : int ndetected = 0;
685 : :
686 : : if (!rnp->exp_tasks)
687 : : return 0;
688 : : t = list_entry(rnp->exp_tasks->prev,
689 : : struct task_struct, rcu_node_entry);
690 : : list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
691 : : pr_cont(" P%d", t->pid);
692 : : ndetected++;
693 : : }
694 : : return ndetected;
695 : : }
696 : :
697 : : #else /* #ifdef CONFIG_PREEMPT_RCU */
698 : :
699 : : /* Request an expedited quiescent state. */
700 : 3412 : static void rcu_exp_need_qs(void)
701 : : {
702 : 6824 : __this_cpu_write(rcu_data.cpu_no_qs.b.exp, true);
703 : : /* Store .exp before .rcu_urgent_qs. */
704 : 6826 : smp_store_release(this_cpu_ptr(&rcu_data.rcu_urgent_qs), true);
705 : 3414 : set_tsk_need_resched(current);
706 : : set_preempt_need_resched();
707 : 3414 : }
708 : :
709 : : /* Invoked on each online non-idle CPU for expedited quiescent state. */
710 : 3514 : static void rcu_exp_handler(void *unused)
711 : : {
712 : : struct rcu_data *rdp;
713 : : struct rcu_node *rnp;
714 : :
715 : 7028 : rdp = this_cpu_ptr(&rcu_data);
716 : 3514 : rnp = rdp->mynode;
717 [ + - + + ]: 7028 : if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
718 : 7028 : __this_cpu_read(rcu_data.cpu_no_qs.b.exp))
719 : : return;
720 [ + + ]: 3512 : if (rcu_is_cpu_rrupt_from_idle()) {
721 : 200 : rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
722 : : return;
723 : : }
724 : 3412 : rcu_exp_need_qs();
725 : : }
726 : :
727 : : /* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
728 : 1212 : static void sync_sched_exp_online_cleanup(int cpu)
729 : : {
730 : : unsigned long flags;
731 : : int my_cpu;
732 : : struct rcu_data *rdp;
733 : : int ret;
734 : : struct rcu_node *rnp;
735 : :
736 : 1212 : rdp = per_cpu_ptr(&rcu_data, cpu);
737 : 1212 : rnp = rdp->mynode;
738 : 2424 : my_cpu = get_cpu();
739 : : /* Quiescent state either not needed or already requested, leave. */
740 [ - + # # ]: 1212 : if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
741 : 0 : __this_cpu_read(rcu_data.cpu_no_qs.b.exp)) {
742 : 1212 : put_cpu();
743 : 1212 : return;
744 : : }
745 : : /* Quiescent state needed on current CPU, so set it up locally. */
746 [ # # ]: 0 : if (my_cpu == cpu) {
747 : 0 : local_irq_save(flags);
748 : 0 : rcu_exp_need_qs();
749 [ # # ]: 0 : local_irq_restore(flags);
750 : 0 : put_cpu();
751 : 0 : return;
752 : : }
753 : : /* Quiescent state needed on some other CPU, send IPI. */
754 : 0 : ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
755 : 0 : put_cpu();
756 [ # # # # ]: 0 : WARN_ON_ONCE(ret);
757 : : }
758 : :
759 : : /*
760 : : * Because preemptible RCU does not exist, we never have to check for
761 : : * tasks blocked within RCU read-side critical sections that are
762 : : * blocking the current expedited grace period.
763 : : */
764 : : static int rcu_print_task_exp_stall(struct rcu_node *rnp)
765 : : {
766 : : return 0;
767 : : }
768 : :
769 : : #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
770 : :
771 : : /**
772 : : * synchronize_rcu_expedited - Brute-force RCU grace period
773 : : *
774 : : * Wait for an RCU grace period, but expedite it. The basic idea is to
775 : : * IPI all non-idle non-nohz online CPUs. The IPI handler checks whether
776 : : * the CPU is in an RCU critical section, and if so, it sets a flag that
777 : : * causes the outermost rcu_read_unlock() to report the quiescent state
778 : : * for RCU-preempt or asks the scheduler for help for RCU-sched. On the
779 : : * other hand, if the CPU is not in an RCU read-side critical section,
780 : : * the IPI handler reports the quiescent state immediately.
781 : : *
782 : : * Although this is a great improvement over previous expedited
783 : : * implementations, it is still unfriendly to real-time workloads, so is
784 : : * thus not recommended for any sort of common-case code. In fact, if
785 : : * you are using synchronize_rcu_expedited() in a loop, please restructure
786 : : * your code to batch your updates, and then Use a single synchronize_rcu()
787 : : * instead.
788 : : *
789 : : * This has the same semantics as (but is more brutal than) synchronize_rcu().
790 : : */
791 : 5656 : void synchronize_rcu_expedited(void)
792 : : {
793 : 5656 : bool boottime = (rcu_scheduler_active == RCU_SCHEDULER_INIT);
794 : : struct rcu_exp_work rew;
795 : : struct rcu_node *rnp;
796 : : unsigned long s;
797 : :
798 : : RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
799 : : lock_is_held(&rcu_lock_map) ||
800 : : lock_is_held(&rcu_sched_lock_map),
801 : : "Illegal synchronize_rcu_expedited() in RCU read-side critical section");
802 : :
803 : : /* Is the state is such that the call is a grace period? */
804 [ + - ]: 5656 : if (rcu_blocking_is_gp())
805 : 0 : return;
806 : :
807 : : /* If expedited grace periods are prohibited, fall back to normal. */
808 [ - + ]: 5656 : if (rcu_gp_is_normal()) {
809 : 0 : wait_rcu_gp(call_rcu);
810 : 0 : return;
811 : : }
812 : :
813 : : /* Take a snapshot of the sequence number. */
814 : : s = rcu_exp_gp_seq_snap();
815 [ + - ]: 5656 : if (exp_funnel_lock(s))
816 : : return; /* Someone else did our work for us. */
817 : :
818 : : /* Ensure that load happens before action based on it. */
819 [ - + ]: 5656 : if (unlikely(boottime)) {
820 : : /* Direct call during scheduler init and early_initcalls(). */
821 : : rcu_exp_sel_wait_wake(s);
822 : : } else {
823 : : /* Marshall arguments & schedule the expedited grace period. */
824 : 5656 : rew.rew_s = s;
825 : 11312 : INIT_WORK_ONSTACK(&rew.rew_work, wait_rcu_exp_gp);
826 : 5656 : queue_work(rcu_gp_wq, &rew.rew_work);
827 : : }
828 : :
829 : : /* Wait for expedited grace period to complete. */
830 : : rnp = rcu_get_root();
831 [ + + + + ]: 16280 : wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
832 : : sync_exp_work_done(s));
833 : 5656 : smp_mb(); /* Workqueue actions happen before return. */
834 : :
835 : : /* Let the next expedited grace period start. */
836 : 5656 : mutex_unlock(&rcu_state.exp_mutex);
837 : :
838 : : if (likely(!boottime))
839 : : destroy_work_on_stack(&rew.rew_work);
840 : : }
841 : : EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
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