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1 : : // SPDX-License-Identifier: GPL-2.0+
2 : : /*
3 : : * RCU CPU stall warnings for normal RCU grace periods
4 : : *
5 : : * Copyright IBM Corporation, 2019
6 : : *
7 : : * Author: Paul E. McKenney <paulmck@linux.ibm.com>
8 : : */
9 : :
10 : : //////////////////////////////////////////////////////////////////////////////
11 : : //
12 : : // Controlling CPU stall warnings, including delay calculation.
13 : :
14 : : /* panic() on RCU Stall sysctl. */
15 : : int sysctl_panic_on_rcu_stall __read_mostly;
16 : :
17 : : #ifdef CONFIG_PROVE_RCU
18 : : #define RCU_STALL_DELAY_DELTA (5 * HZ)
19 : : #else
20 : : #define RCU_STALL_DELAY_DELTA 0
21 : : #endif
22 : :
23 : : /* Limit-check stall timeouts specified at boottime and runtime. */
24 : 0 : int rcu_jiffies_till_stall_check(void)
25 : : {
26 : 4137913 : int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout);
27 : :
28 : : /*
29 : : * Limit check must be consistent with the Kconfig limits
30 : : * for CONFIG_RCU_CPU_STALL_TIMEOUT.
31 : : */
32 [ - + # # : 4137913 : if (till_stall_check < 3) {
# # # # #
# - + # #
- + ]
33 : : WRITE_ONCE(rcu_cpu_stall_timeout, 3);
34 : : till_stall_check = 3;
35 [ - + # # : 4137913 : } else if (till_stall_check > 300) {
# # # # #
# - + # #
- + ]
36 : : WRITE_ONCE(rcu_cpu_stall_timeout, 300);
37 : : till_stall_check = 300;
38 : : }
39 : 283326 : return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
40 : : }
41 : : EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check);
42 : :
43 : : /* Don't do RCU CPU stall warnings during long sysrq printouts. */
44 : 0 : void rcu_sysrq_start(void)
45 : : {
46 [ # # ]: 0 : if (!rcu_cpu_stall_suppress)
47 : 0 : rcu_cpu_stall_suppress = 2;
48 : 0 : }
49 : :
50 : 0 : void rcu_sysrq_end(void)
51 : : {
52 [ # # ]: 0 : if (rcu_cpu_stall_suppress == 2)
53 : 0 : rcu_cpu_stall_suppress = 0;
54 : 0 : }
55 : :
56 : : /* Don't print RCU CPU stall warnings during a kernel panic. */
57 : 0 : static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
58 : : {
59 : 0 : rcu_cpu_stall_suppress = 1;
60 : 0 : return NOTIFY_DONE;
61 : : }
62 : :
63 : : static struct notifier_block rcu_panic_block = {
64 : : .notifier_call = rcu_panic,
65 : : };
66 : :
67 : 207 : static int __init check_cpu_stall_init(void)
68 : : {
69 : 207 : atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
70 : 207 : return 0;
71 : : }
72 : : early_initcall(check_cpu_stall_init);
73 : :
74 : : /* If so specified via sysctl, panic, yielding cleaner stall-warning output. */
75 : : static void panic_on_rcu_stall(void)
76 : : {
77 [ # # # # : 0 : if (sysctl_panic_on_rcu_stall)
# # ]
78 : 0 : panic("RCU Stall\n");
79 : : }
80 : :
81 : : /**
82 : : * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
83 : : *
84 : : * Set the stall-warning timeout way off into the future, thus preventing
85 : : * any RCU CPU stall-warning messages from appearing in the current set of
86 : : * RCU grace periods.
87 : : *
88 : : * The caller must disable hard irqs.
89 : : */
90 : 0 : void rcu_cpu_stall_reset(void)
91 : : {
92 : 0 : WRITE_ONCE(rcu_state.jiffies_stall, jiffies + ULONG_MAX / 2);
93 : 0 : }
94 : :
95 : : //////////////////////////////////////////////////////////////////////////////
96 : : //
97 : : // Interaction with RCU grace periods
98 : :
99 : : /* Start of new grace period, so record stall time (and forcing times). */
100 : 280210 : static void record_gp_stall_check_time(void)
101 : : {
102 : 280210 : unsigned long j = jiffies;
103 : : unsigned long j1;
104 : :
105 : 280210 : rcu_state.gp_start = j;
106 : 280210 : j1 = rcu_jiffies_till_stall_check();
107 : : /* Record ->gp_start before ->jiffies_stall. */
108 : 280210 : smp_store_release(&rcu_state.jiffies_stall, j + j1); /* ^^^ */
109 : 280210 : rcu_state.jiffies_resched = j + j1 / 2;
110 : 280210 : rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs);
111 : 280210 : }
112 : :
113 : : /* Zero ->ticks_this_gp and snapshot the number of RCU softirq handlers. */
114 : : static void zero_cpu_stall_ticks(struct rcu_data *rdp)
115 : : {
116 : 991699 : rdp->ticks_this_gp = 0;
117 : 1983398 : rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
118 : 991699 : WRITE_ONCE(rdp->last_fqs_resched, jiffies);
119 : : }
120 : :
121 : : /*
122 : : * If too much time has passed in the current grace period, and if
123 : : * so configured, go kick the relevant kthreads.
124 : : */
125 : 2635697 : static void rcu_stall_kick_kthreads(void)
126 : : {
127 : : unsigned long j;
128 : :
129 [ - + ]: 2635697 : if (!rcu_kick_kthreads)
130 : 2635697 : return;
131 : : j = READ_ONCE(rcu_state.jiffies_kick_kthreads);
132 [ # # # # : 0 : if (time_after(jiffies, j) && rcu_state.gp_kthread &&
# # ]
133 [ # # ]: 0 : (rcu_gp_in_progress() || READ_ONCE(rcu_state.gp_flags))) {
134 [ # # ]: 0 : WARN_ONCE(1, "Kicking %s grace-period kthread\n",
135 : : rcu_state.name);
136 [ # # # # : 0 : rcu_ftrace_dump(DUMP_ALL);
# # # # ]
137 : 0 : wake_up_process(rcu_state.gp_kthread);
138 : 0 : WRITE_ONCE(rcu_state.jiffies_kick_kthreads, j + HZ);
139 : : }
140 : : }
141 : :
142 : : /*
143 : : * Handler for the irq_work request posted about halfway into the RCU CPU
144 : : * stall timeout, and used to detect excessive irq disabling. Set state
145 : : * appropriately, but just complain if there is unexpected state on entry.
146 : : */
147 : 0 : static void rcu_iw_handler(struct irq_work *iwp)
148 : : {
149 : : struct rcu_data *rdp;
150 : : struct rcu_node *rnp;
151 : :
152 : : rdp = container_of(iwp, struct rcu_data, rcu_iw);
153 : 0 : rnp = rdp->mynode;
154 : 0 : raw_spin_lock_rcu_node(rnp);
155 [ # # # # : 0 : if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
# # ]
156 : 0 : rdp->rcu_iw_gp_seq = rnp->gp_seq;
157 : 0 : rdp->rcu_iw_pending = false;
158 : : }
159 : : raw_spin_unlock_rcu_node(rnp);
160 : 0 : }
161 : :
162 : : //////////////////////////////////////////////////////////////////////////////
163 : : //
164 : : // Printing RCU CPU stall warnings
165 : :
166 : : #ifdef CONFIG_PREEMPTION
167 : :
168 : : /*
169 : : * Dump detailed information for all tasks blocking the current RCU
170 : : * grace period on the specified rcu_node structure.
171 : : */
172 : : static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
173 : : {
174 : : unsigned long flags;
175 : : struct task_struct *t;
176 : :
177 : : raw_spin_lock_irqsave_rcu_node(rnp, flags);
178 : : if (!rcu_preempt_blocked_readers_cgp(rnp)) {
179 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
180 : : return;
181 : : }
182 : : t = list_entry(rnp->gp_tasks->prev,
183 : : struct task_struct, rcu_node_entry);
184 : : list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
185 : : /*
186 : : * We could be printing a lot while holding a spinlock.
187 : : * Avoid triggering hard lockup.
188 : : */
189 : : touch_nmi_watchdog();
190 : : sched_show_task(t);
191 : : }
192 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
193 : : }
194 : :
195 : : /*
196 : : * Scan the current list of tasks blocked within RCU read-side critical
197 : : * sections, printing out the tid of each.
198 : : */
199 : : static int rcu_print_task_stall(struct rcu_node *rnp)
200 : : {
201 : : struct task_struct *t;
202 : : int ndetected = 0;
203 : :
204 : : if (!rcu_preempt_blocked_readers_cgp(rnp))
205 : : return 0;
206 : : pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
207 : : rnp->level, rnp->grplo, rnp->grphi);
208 : : t = list_entry(rnp->gp_tasks->prev,
209 : : struct task_struct, rcu_node_entry);
210 : : list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
211 : : pr_cont(" P%d", t->pid);
212 : : ndetected++;
213 : : }
214 : : pr_cont("\n");
215 : : return ndetected;
216 : : }
217 : :
218 : : #else /* #ifdef CONFIG_PREEMPTION */
219 : :
220 : : /*
221 : : * Because preemptible RCU does not exist, we never have to check for
222 : : * tasks blocked within RCU read-side critical sections.
223 : : */
224 : : static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
225 : : {
226 : : }
227 : :
228 : : /*
229 : : * Because preemptible RCU does not exist, we never have to check for
230 : : * tasks blocked within RCU read-side critical sections.
231 : : */
232 : : static int rcu_print_task_stall(struct rcu_node *rnp)
233 : : {
234 : : return 0;
235 : : }
236 : : #endif /* #else #ifdef CONFIG_PREEMPTION */
237 : :
238 : : /*
239 : : * Dump stacks of all tasks running on stalled CPUs. First try using
240 : : * NMIs, but fall back to manual remote stack tracing on architectures
241 : : * that don't support NMI-based stack dumps. The NMI-triggered stack
242 : : * traces are more accurate because they are printed by the target CPU.
243 : : */
244 : 0 : static void rcu_dump_cpu_stacks(void)
245 : : {
246 : : int cpu;
247 : : unsigned long flags;
248 : : struct rcu_node *rnp;
249 : :
250 [ # # ]: 0 : rcu_for_each_leaf_node(rnp) {
251 : 0 : raw_spin_lock_irqsave_rcu_node(rnp, flags);
252 [ # # ]: 0 : for_each_leaf_node_possible_cpu(rnp, cpu)
253 [ # # ]: 0 : if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
254 [ # # ]: 0 : if (!trigger_single_cpu_backtrace(cpu))
255 : 0 : dump_cpu_task(cpu);
256 : 0 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
257 : : }
258 : 0 : }
259 : :
260 : : #ifdef CONFIG_RCU_FAST_NO_HZ
261 : :
262 : : static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
263 : : {
264 : : struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
265 : :
266 : : sprintf(cp, "last_accelerate: %04lx/%04lx, Nonlazy posted: %c%c%c",
267 : : rdp->last_accelerate & 0xffff, jiffies & 0xffff,
268 : : ".l"[rdp->all_lazy],
269 : : ".L"[!rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)],
270 : : ".D"[!!rdp->tick_nohz_enabled_snap]);
271 : : }
272 : :
273 : : #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
274 : :
275 : : static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
276 : : {
277 : 0 : *cp = '\0';
278 : : }
279 : :
280 : : #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
281 : :
282 : : /*
283 : : * Print out diagnostic information for the specified stalled CPU.
284 : : *
285 : : * If the specified CPU is aware of the current RCU grace period, then
286 : : * print the number of scheduling clock interrupts the CPU has taken
287 : : * during the time that it has been aware. Otherwise, print the number
288 : : * of RCU grace periods that this CPU is ignorant of, for example, "1"
289 : : * if the CPU was aware of the previous grace period.
290 : : *
291 : : * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
292 : : */
293 : 0 : static void print_cpu_stall_info(int cpu)
294 : : {
295 : : unsigned long delta;
296 : : char fast_no_hz[72];
297 : 0 : struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
298 : : char *ticks_title;
299 : : unsigned long ticks_value;
300 : :
301 : : /*
302 : : * We could be printing a lot while holding a spinlock. Avoid
303 : : * triggering hard lockup.
304 : : */
305 : : touch_nmi_watchdog();
306 : :
307 : 0 : ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq);
308 [ # # ]: 0 : if (ticks_value) {
309 : : ticks_title = "GPs behind";
310 : : } else {
311 : : ticks_title = "ticks this GP";
312 : 0 : ticks_value = rdp->ticks_this_gp;
313 : : }
314 : : print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
315 : 0 : delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
316 [ # # ]: 0 : pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n",
317 : : cpu,
318 : : "O."[!!cpu_online(cpu)],
319 : : "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
320 : : "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
321 : : !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
322 : : rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
323 : : "!."[!delta],
324 : : ticks_value, ticks_title,
325 : : rcu_dynticks_snap(rdp) & 0xfff,
326 : : rdp->dynticks_nesting, rdp->dynticks_nmi_nesting,
327 : : rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
328 : : READ_ONCE(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,
329 : : fast_no_hz);
330 : 0 : }
331 : :
332 : : /* Complain about starvation of grace-period kthread. */
333 : 0 : static void rcu_check_gp_kthread_starvation(void)
334 : : {
335 : 0 : struct task_struct *gpk = rcu_state.gp_kthread;
336 : : unsigned long j;
337 : :
338 : 0 : j = jiffies - READ_ONCE(rcu_state.gp_activity);
339 [ # # ]: 0 : if (j > 2 * HZ) {
340 [ # # # # ]: 0 : pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
341 : : rcu_state.name, j,
342 : : (long)rcu_seq_current(&rcu_state.gp_seq),
343 : : READ_ONCE(rcu_state.gp_flags),
344 : : gp_state_getname(rcu_state.gp_state), rcu_state.gp_state,
345 : : gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1);
346 [ # # ]: 0 : if (gpk) {
347 : 0 : pr_err("RCU grace-period kthread stack dump:\n");
348 : 0 : sched_show_task(gpk);
349 : 0 : wake_up_process(gpk);
350 : : }
351 : : }
352 : 0 : }
353 : :
354 : 0 : static void print_other_cpu_stall(unsigned long gp_seq)
355 : : {
356 : : int cpu;
357 : : unsigned long flags;
358 : : unsigned long gpa;
359 : : unsigned long j;
360 : : int ndetected = 0;
361 : : struct rcu_node *rnp;
362 : : long totqlen = 0;
363 : :
364 : : /* Kick and suppress, if so configured. */
365 : 0 : rcu_stall_kick_kthreads();
366 [ # # ]: 0 : if (rcu_cpu_stall_suppress)
367 : 0 : return;
368 : :
369 : : /*
370 : : * OK, time to rat on our buddy...
371 : : * See Documentation/RCU/stallwarn.txt for info on how to debug
372 : : * RCU CPU stall warnings.
373 : : */
374 : 0 : pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name);
375 [ # # ]: 0 : rcu_for_each_leaf_node(rnp) {
376 : 0 : raw_spin_lock_irqsave_rcu_node(rnp, flags);
377 : : ndetected += rcu_print_task_stall(rnp);
378 [ # # ]: 0 : if (rnp->qsmask != 0) {
379 [ # # ]: 0 : for_each_leaf_node_possible_cpu(rnp, cpu)
380 [ # # ]: 0 : if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
381 : 0 : print_cpu_stall_info(cpu);
382 : 0 : ndetected++;
383 : : }
384 : : }
385 : 0 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
386 : : }
387 : :
388 [ # # ]: 0 : for_each_possible_cpu(cpu)
389 : 0 : totqlen += rcu_get_n_cbs_cpu(cpu);
390 : 0 : pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n",
391 : : smp_processor_id(), (long)(jiffies - rcu_state.gp_start),
392 : : (long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
393 [ # # ]: 0 : if (ndetected) {
394 : 0 : rcu_dump_cpu_stacks();
395 : :
396 : : /* Complain about tasks blocking the grace period. */
397 [ # # ]: 0 : rcu_for_each_leaf_node(rnp)
398 : : rcu_print_detail_task_stall_rnp(rnp);
399 : : } else {
400 [ # # ]: 0 : if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) {
401 : 0 : pr_err("INFO: Stall ended before state dump start\n");
402 : : } else {
403 : 0 : j = jiffies;
404 : : gpa = READ_ONCE(rcu_state.gp_activity);
405 : 0 : pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
406 : : rcu_state.name, j - gpa, j, gpa,
407 : : READ_ONCE(jiffies_till_next_fqs),
408 : : rcu_get_root()->qsmask);
409 : : /* In this case, the current CPU might be at fault. */
410 : 0 : sched_show_task(current);
411 : : }
412 : : }
413 : : /* Rewrite if needed in case of slow consoles. */
414 [ # # ]: 0 : if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
415 : 0 : WRITE_ONCE(rcu_state.jiffies_stall,
416 : : jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
417 : :
418 : 0 : rcu_check_gp_kthread_starvation();
419 : :
420 : : panic_on_rcu_stall();
421 : :
422 : 0 : rcu_force_quiescent_state(); /* Kick them all. */
423 : : }
424 : :
425 : 0 : static void print_cpu_stall(void)
426 : : {
427 : : int cpu;
428 : : unsigned long flags;
429 : 0 : struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
430 : : struct rcu_node *rnp = rcu_get_root();
431 : : long totqlen = 0;
432 : :
433 : : /* Kick and suppress, if so configured. */
434 : 0 : rcu_stall_kick_kthreads();
435 [ # # ]: 0 : if (rcu_cpu_stall_suppress)
436 : 0 : return;
437 : :
438 : : /*
439 : : * OK, time to rat on ourselves...
440 : : * See Documentation/RCU/stallwarn.txt for info on how to debug
441 : : * RCU CPU stall warnings.
442 : : */
443 : 0 : pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name);
444 : 0 : raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
445 : 0 : print_cpu_stall_info(smp_processor_id());
446 : 0 : raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
447 [ # # ]: 0 : for_each_possible_cpu(cpu)
448 : 0 : totqlen += rcu_get_n_cbs_cpu(cpu);
449 : 0 : pr_cont("\t(t=%lu jiffies g=%ld q=%lu)\n",
450 : : jiffies - rcu_state.gp_start,
451 : : (long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
452 : :
453 : 0 : rcu_check_gp_kthread_starvation();
454 : :
455 : 0 : rcu_dump_cpu_stacks();
456 : :
457 : 0 : raw_spin_lock_irqsave_rcu_node(rnp, flags);
458 : : /* Rewrite if needed in case of slow consoles. */
459 [ # # ]: 0 : if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
460 : 0 : WRITE_ONCE(rcu_state.jiffies_stall,
461 : : jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
462 : 0 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
463 : :
464 : : panic_on_rcu_stall();
465 : :
466 : : /*
467 : : * Attempt to revive the RCU machinery by forcing a context switch.
468 : : *
469 : : * A context switch would normally allow the RCU state machine to make
470 : : * progress and it could be we're stuck in kernel space without context
471 : : * switches for an entirely unreasonable amount of time.
472 : : */
473 : 0 : set_tsk_need_resched(current);
474 : : set_preempt_need_resched();
475 : : }
476 : :
477 : 2611053 : static void check_cpu_stall(struct rcu_data *rdp)
478 : : {
479 : : unsigned long gs1;
480 : : unsigned long gs2;
481 : : unsigned long gps;
482 : : unsigned long j;
483 : : unsigned long jn;
484 : : unsigned long js;
485 : : struct rcu_node *rnp;
486 : :
487 [ - + # # : 5409994 : if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
+ + ]
488 : : !rcu_gp_in_progress())
489 : : return;
490 : 2633387 : rcu_stall_kick_kthreads();
491 : 2197727 : j = jiffies;
492 : :
493 : : /*
494 : : * Lots of memory barriers to reject false positives.
495 : : *
496 : : * The idea is to pick up rcu_state.gp_seq, then
497 : : * rcu_state.jiffies_stall, then rcu_state.gp_start, and finally
498 : : * another copy of rcu_state.gp_seq. These values are updated in
499 : : * the opposite order with memory barriers (or equivalent) during
500 : : * grace-period initialization and cleanup. Now, a false positive
501 : : * can occur if we get an new value of rcu_state.gp_start and a old
502 : : * value of rcu_state.jiffies_stall. But given the memory barriers,
503 : : * the only way that this can happen is if one grace period ends
504 : : * and another starts between these two fetches. This is detected
505 : : * by comparing the second fetch of rcu_state.gp_seq with the
506 : : * previous fetch from rcu_state.gp_seq.
507 : : *
508 : : * Given this check, comparisons of jiffies, rcu_state.jiffies_stall,
509 : : * and rcu_state.gp_start suffice to forestall false positives.
510 : : */
511 : : gs1 = READ_ONCE(rcu_state.gp_seq);
512 : 2197727 : smp_rmb(); /* Pick up ->gp_seq first... */
513 : : js = READ_ONCE(rcu_state.jiffies_stall);
514 : 2062489 : smp_rmb(); /* ...then ->jiffies_stall before the rest... */
515 : : gps = READ_ONCE(rcu_state.gp_start);
516 : 2353243 : smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */
517 : : gs2 = READ_ONCE(rcu_state.gp_seq);
518 [ + - - + ]: 4833906 : if (gs1 != gs2 ||
519 [ # # ]: 2457206 : ULONG_CMP_LT(j, js) ||
520 : 0 : ULONG_CMP_GE(gps, js))
521 : : return; /* No stall or GP completed since entering function. */
522 : 0 : rnp = rdp->mynode;
523 : 0 : jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
524 [ # # # # ]: 0 : if (rcu_gp_in_progress() &&
525 [ # # ]: 0 : (READ_ONCE(rnp->qsmask) & rdp->grpmask) &&
526 : 0 : cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
527 : :
528 : : /* We haven't checked in, so go dump stack. */
529 : 0 : print_cpu_stall();
530 [ # # ]: 0 : if (rcu_cpu_stall_ftrace_dump)
531 [ # # # # : 0 : rcu_ftrace_dump(DUMP_ALL);
# # # # ]
532 : :
533 [ # # # # ]: 0 : } else if (rcu_gp_in_progress() &&
534 [ # # ]: 0 : ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) &&
535 : 0 : cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
536 : :
537 : : /* They had a few time units to dump stack, so complain. */
538 : 0 : print_other_cpu_stall(gs2);
539 [ # # ]: 0 : if (rcu_cpu_stall_ftrace_dump)
540 [ # # # # : 0 : rcu_ftrace_dump(DUMP_ALL);
# # # # ]
541 : : }
542 : : }
543 : :
544 : : //////////////////////////////////////////////////////////////////////////////
545 : : //
546 : : // RCU forward-progress mechanisms, including of callback invocation.
547 : :
548 : :
549 : : /*
550 : : * Show the state of the grace-period kthreads.
551 : : */
552 : 0 : void show_rcu_gp_kthreads(void)
553 : : {
554 : : int cpu;
555 : : unsigned long j;
556 : : unsigned long ja;
557 : : unsigned long jr;
558 : : unsigned long jw;
559 : : struct rcu_data *rdp;
560 : : struct rcu_node *rnp;
561 : :
562 : 0 : j = jiffies;
563 : 0 : ja = j - READ_ONCE(rcu_state.gp_activity);
564 : 0 : jr = j - READ_ONCE(rcu_state.gp_req_activity);
565 : 0 : jw = j - READ_ONCE(rcu_state.gp_wake_time);
566 [ # # ]: 0 : pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_flags %#x\n",
567 : : rcu_state.name, gp_state_getname(rcu_state.gp_state),
568 : : rcu_state.gp_state,
569 : : rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL,
570 : : ja, jr, jw, (long)READ_ONCE(rcu_state.gp_wake_seq),
571 : : (long)READ_ONCE(rcu_state.gp_seq),
572 : : (long)READ_ONCE(rcu_get_root()->gp_seq_needed),
573 : : READ_ONCE(rcu_state.gp_flags));
574 [ # # ]: 0 : rcu_for_each_node_breadth_first(rnp) {
575 [ # # ]: 0 : if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed))
576 : 0 : continue;
577 : 0 : pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n",
578 : : rnp->grplo, rnp->grphi, (long)rnp->gp_seq,
579 : : (long)rnp->gp_seq_needed);
580 [ # # ]: 0 : if (!rcu_is_leaf_node(rnp))
581 : 0 : continue;
582 [ # # ]: 0 : for_each_leaf_node_possible_cpu(rnp, cpu) {
583 : 0 : rdp = per_cpu_ptr(&rcu_data, cpu);
584 [ # # # # ]: 0 : if (rdp->gpwrap ||
585 : 0 : ULONG_CMP_GE(rcu_state.gp_seq,
586 : : rdp->gp_seq_needed))
587 : 0 : continue;
588 : 0 : pr_info("\tcpu %d ->gp_seq_needed %ld\n",
589 : : cpu, (long)rdp->gp_seq_needed);
590 : : }
591 : : }
592 [ # # ]: 0 : for_each_possible_cpu(cpu) {
593 : 0 : rdp = per_cpu_ptr(&rcu_data, cpu);
594 : : if (rcu_segcblist_is_offloaded(&rdp->cblist))
595 : : show_rcu_nocb_state(rdp);
596 : : }
597 : : /* sched_show_task(rcu_state.gp_kthread); */
598 : 0 : }
599 : : EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
600 : :
601 : : /*
602 : : * This function checks for grace-period requests that fail to motivate
603 : : * RCU to come out of its idle mode.
604 : : */
605 : : static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
606 : : const unsigned long gpssdelay)
607 : : {
608 : : unsigned long flags;
609 : : unsigned long j;
610 : : struct rcu_node *rnp_root = rcu_get_root();
611 : : static atomic_t warned = ATOMIC_INIT(0);
612 : :
613 : : if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||
614 : : ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed))
615 : : return;
616 : : j = jiffies; /* Expensive access, and in common case don't get here. */
617 : : if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
618 : : time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
619 : : atomic_read(&warned))
620 : : return;
621 : :
622 : : raw_spin_lock_irqsave_rcu_node(rnp, flags);
623 : : j = jiffies;
624 : : if (rcu_gp_in_progress() ||
625 : : ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
626 : : time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
627 : : time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
628 : : atomic_read(&warned)) {
629 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
630 : : return;
631 : : }
632 : : /* Hold onto the leaf lock to make others see warned==1. */
633 : :
634 : : if (rnp_root != rnp)
635 : : raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
636 : : j = jiffies;
637 : : if (rcu_gp_in_progress() ||
638 : : ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
639 : : time_before(j, rcu_state.gp_req_activity + gpssdelay) ||
640 : : time_before(j, rcu_state.gp_activity + gpssdelay) ||
641 : : atomic_xchg(&warned, 1)) {
642 : : if (rnp_root != rnp)
643 : : /* irqs remain disabled. */
644 : : raw_spin_unlock_rcu_node(rnp_root);
645 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
646 : : return;
647 : : }
648 : : WARN_ON(1);
649 : : if (rnp_root != rnp)
650 : : raw_spin_unlock_rcu_node(rnp_root);
651 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
652 : : show_rcu_gp_kthreads();
653 : : }
654 : :
655 : : /*
656 : : * Do a forward-progress check for rcutorture. This is normally invoked
657 : : * due to an OOM event. The argument "j" gives the time period during
658 : : * which rcutorture would like progress to have been made.
659 : : */
660 : 0 : void rcu_fwd_progress_check(unsigned long j)
661 : : {
662 : : unsigned long cbs;
663 : : int cpu;
664 : : unsigned long max_cbs = 0;
665 : : int max_cpu = -1;
666 : : struct rcu_data *rdp;
667 : :
668 [ # # ]: 0 : if (rcu_gp_in_progress()) {
669 : 0 : pr_info("%s: GP age %lu jiffies\n",
670 : : __func__, jiffies - rcu_state.gp_start);
671 : 0 : show_rcu_gp_kthreads();
672 : : } else {
673 : 0 : pr_info("%s: Last GP end %lu jiffies ago\n",
674 : : __func__, jiffies - rcu_state.gp_end);
675 : 0 : preempt_disable();
676 : 0 : rdp = this_cpu_ptr(&rcu_data);
677 : : rcu_check_gp_start_stall(rdp->mynode, rdp, j);
678 : 0 : preempt_enable();
679 : : }
680 [ # # ]: 0 : for_each_possible_cpu(cpu) {
681 : 0 : cbs = rcu_get_n_cbs_cpu(cpu);
682 [ # # ]: 0 : if (!cbs)
683 : 0 : continue;
684 [ # # ]: 0 : if (max_cpu < 0)
685 : 0 : pr_info("%s: callbacks", __func__);
686 : 0 : pr_cont(" %d: %lu", cpu, cbs);
687 [ # # ]: 0 : if (cbs <= max_cbs)
688 : 0 : continue;
689 : : max_cbs = cbs;
690 : : max_cpu = cpu;
691 : : }
692 [ # # ]: 0 : if (max_cpu >= 0)
693 : 0 : pr_cont("\n");
694 : 0 : }
695 : : EXPORT_SYMBOL_GPL(rcu_fwd_progress_check);
696 : :
697 : : /* Commandeer a sysrq key to dump RCU's tree. */
698 : : static bool sysrq_rcu;
699 : : module_param(sysrq_rcu, bool, 0444);
700 : :
701 : : /* Dump grace-period-request information due to commandeered sysrq. */
702 : 0 : static void sysrq_show_rcu(int key)
703 : : {
704 : 0 : show_rcu_gp_kthreads();
705 : 0 : }
706 : :
707 : : static struct sysrq_key_op sysrq_rcudump_op = {
708 : : .handler = sysrq_show_rcu,
709 : : .help_msg = "show-rcu(y)",
710 : : .action_msg = "Show RCU tree",
711 : : .enable_mask = SYSRQ_ENABLE_DUMP,
712 : : };
713 : :
714 : 207 : static int __init rcu_sysrq_init(void)
715 : : {
716 [ - + ]: 207 : if (sysrq_rcu)
717 : 0 : return register_sysrq_key('y', &sysrq_rcudump_op);
718 : : return 0;
719 : : }
720 : : early_initcall(rcu_sysrq_init);
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