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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 : 315533 : int rcu_jiffies_till_stall_check(void)
25 : : {
26 [ - - - - : 247986 : 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 [ - - - - : 315533 : if (till_stall_check < 3) {
- - - - -
+ - - -
+ ]
33 : 0 : WRITE_ONCE(rcu_cpu_stall_timeout, 3);
34 : 0 : till_stall_check = 3;
35 [ - - - - : 315533 : } else if (till_stall_check > 300) {
- - - - -
+ - - -
+ ]
36 : 0 : WRITE_ONCE(rcu_cpu_stall_timeout, 300);
37 : 0 : till_stall_check = 300;
38 : : }
39 : 0 : 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 : 30 : static int __init check_cpu_stall_init(void)
68 : : {
69 : 30 : atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
70 : 30 : return 0;
71 : : }
72 : : early_initcall(check_cpu_stall_init);
73 : :
74 : : /* If so specified via sysctl, panic, yielding cleaner stall-warning output. */
75 : 0 : 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 : 30 : void rcu_cpu_stall_reset(void)
91 : : {
92 : 30 : WRITE_ONCE(rcu_state.jiffies_stall, jiffies + ULONG_MAX / 2);
93 : 30 : }
94 : :
95 : : //////////////////////////////////////////////////////////////////////////////
96 : : //
97 : : // Interaction with RCU grace periods
98 : :
99 : : /* Start of new grace period, so record stall time (and forcing times). */
100 : 67547 : static void record_gp_stall_check_time(void)
101 : : {
102 : 67547 : unsigned long j = jiffies;
103 : 67547 : unsigned long j1;
104 : :
105 : 67547 : rcu_state.gp_start = j;
106 [ - + ]: 67547 : j1 = rcu_jiffies_till_stall_check();
107 : : /* Record ->gp_start before ->jiffies_stall. */
108 : 67547 : smp_store_release(&rcu_state.jiffies_stall, j + j1); /* ^^^ */
109 : 67547 : rcu_state.jiffies_resched = j + j1 / 2;
110 : 67547 : rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs);
111 : 67547 : }
112 : :
113 : : /* Zero ->ticks_this_gp and snapshot the number of RCU softirq handlers. */
114 : 67551 : static void zero_cpu_stall_ticks(struct rcu_data *rdp)
115 : : {
116 : 67551 : rdp->ticks_this_gp = 0;
117 : 67551 : rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
118 : 67551 : WRITE_ONCE(rdp->last_fqs_resched, jiffies);
119 : 67551 : }
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 : 27503 : static void rcu_stall_kick_kthreads(void)
126 : : {
127 : 27503 : unsigned long j;
128 : :
129 [ - + ]: 27503 : if (!rcu_kick_kthreads)
130 : : return;
131 [ # # ]: 0 : 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 : 0 : struct rcu_data *rdp;
150 : 0 : struct rcu_node *rnp;
151 : :
152 : 0 : 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 : 0 : raw_spin_unlock_rcu_node(rnp);
160 : 0 : }
161 : :
162 : : //////////////////////////////////////////////////////////////////////////////
163 : : //
164 : : // Printing RCU CPU stall warnings
165 : :
166 : : #ifdef CONFIG_PREEMPT_RCU
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_PREEMPT_RCU */
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 : 0 : static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
225 : : {
226 : 0 : }
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 : 0 : static int rcu_print_task_stall(struct rcu_node *rnp)
233 : : {
234 : 0 : return 0;
235 : : }
236 : : #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
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 : 0 : int cpu;
247 : 0 : unsigned long flags;
248 : 0 : 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 : : 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 dyntick_enabled: %d",
267 : : rdp->last_accelerate & 0xffff, jiffies & 0xffff,
268 : : !!rdp->tick_nohz_enabled_snap);
269 : : }
270 : :
271 : : #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
272 : :
273 : 0 : static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
274 : : {
275 : 0 : *cp = '\0';
276 : : }
277 : :
278 : : #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
279 : :
280 : : static const char * const gp_state_names[] = {
281 : : [RCU_GP_IDLE] = "RCU_GP_IDLE",
282 : : [RCU_GP_WAIT_GPS] = "RCU_GP_WAIT_GPS",
283 : : [RCU_GP_DONE_GPS] = "RCU_GP_DONE_GPS",
284 : : [RCU_GP_ONOFF] = "RCU_GP_ONOFF",
285 : : [RCU_GP_INIT] = "RCU_GP_INIT",
286 : : [RCU_GP_WAIT_FQS] = "RCU_GP_WAIT_FQS",
287 : : [RCU_GP_DOING_FQS] = "RCU_GP_DOING_FQS",
288 : : [RCU_GP_CLEANUP] = "RCU_GP_CLEANUP",
289 : : [RCU_GP_CLEANED] = "RCU_GP_CLEANED",
290 : : };
291 : :
292 : : /*
293 : : * Convert a ->gp_state value to a character string.
294 : : */
295 : 0 : static const char *gp_state_getname(short gs)
296 : : {
297 : 0 : if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
298 : : return "???";
299 : 0 : return gp_state_names[gs];
300 : : }
301 : :
302 : : /*
303 : : * Print out diagnostic information for the specified stalled CPU.
304 : : *
305 : : * If the specified CPU is aware of the current RCU grace period, then
306 : : * print the number of scheduling clock interrupts the CPU has taken
307 : : * during the time that it has been aware. Otherwise, print the number
308 : : * of RCU grace periods that this CPU is ignorant of, for example, "1"
309 : : * if the CPU was aware of the previous grace period.
310 : : *
311 : : * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
312 : : */
313 : 0 : static void print_cpu_stall_info(int cpu)
314 : : {
315 : 0 : unsigned long delta;
316 : 0 : char fast_no_hz[72];
317 : 0 : struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
318 : 0 : char *ticks_title;
319 : 0 : unsigned long ticks_value;
320 : :
321 : : /*
322 : : * We could be printing a lot while holding a spinlock. Avoid
323 : : * triggering hard lockup.
324 : : */
325 [ # # ]: 0 : touch_nmi_watchdog();
326 : :
327 [ # # ]: 0 : ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq);
328 [ # # ]: 0 : if (ticks_value) {
329 : : ticks_title = "GPs behind";
330 : : } else {
331 : 0 : ticks_title = "ticks this GP";
332 : 0 : ticks_value = rdp->ticks_this_gp;
333 : : }
334 : 0 : print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
335 : 0 : delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
336 [ # # ]: 0 : pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n",
337 : : cpu,
338 : : "O."[!!cpu_online(cpu)],
339 : : "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
340 : : "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
341 : : !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
342 : : rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
343 : : "!."[!delta],
344 : : ticks_value, ticks_title,
345 : : rcu_dynticks_snap(rdp) & 0xfff,
346 : : rdp->dynticks_nesting, rdp->dynticks_nmi_nesting,
347 : : rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
348 : : READ_ONCE(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,
349 : : fast_no_hz);
350 : 0 : }
351 : :
352 : : /* Complain about starvation of grace-period kthread. */
353 : 0 : static void rcu_check_gp_kthread_starvation(void)
354 : : {
355 : 0 : struct task_struct *gpk = rcu_state.gp_kthread;
356 : 0 : unsigned long j;
357 : :
358 [ # # ]: 0 : j = jiffies - READ_ONCE(rcu_state.gp_activity);
359 [ # # ]: 0 : if (j > 2 * HZ) {
360 [ # # # # : 0 : pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
# # ]
361 : : rcu_state.name, j,
362 : : (long)rcu_seq_current(&rcu_state.gp_seq),
363 : : READ_ONCE(rcu_state.gp_flags),
364 : : gp_state_getname(rcu_state.gp_state), rcu_state.gp_state,
365 : : gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1);
366 [ # # ]: 0 : if (gpk) {
367 : 0 : pr_err("RCU grace-period kthread stack dump:\n");
368 : 0 : sched_show_task(gpk);
369 : 0 : wake_up_process(gpk);
370 : : }
371 : : }
372 : 0 : }
373 : :
374 : 0 : static void print_other_cpu_stall(unsigned long gp_seq)
375 : : {
376 : 0 : int cpu;
377 : 0 : unsigned long flags;
378 : 0 : unsigned long gpa;
379 : 0 : unsigned long j;
380 : 0 : int ndetected = 0;
381 : 0 : struct rcu_node *rnp;
382 : 0 : long totqlen = 0;
383 : :
384 : : /* Kick and suppress, if so configured. */
385 : 0 : rcu_stall_kick_kthreads();
386 [ # # ]: 0 : if (rcu_cpu_stall_suppress)
387 : : return;
388 : :
389 : : /*
390 : : * OK, time to rat on our buddy...
391 : : * See Documentation/RCU/stallwarn.txt for info on how to debug
392 : : * RCU CPU stall warnings.
393 : : */
394 : 0 : pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name);
395 [ # # ]: 0 : rcu_for_each_leaf_node(rnp) {
396 : 0 : raw_spin_lock_irqsave_rcu_node(rnp, flags);
397 : 0 : ndetected += rcu_print_task_stall(rnp);
398 [ # # ]: 0 : if (rnp->qsmask != 0) {
399 [ # # ]: 0 : for_each_leaf_node_possible_cpu(rnp, cpu)
400 [ # # ]: 0 : if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
401 : 0 : print_cpu_stall_info(cpu);
402 : 0 : ndetected++;
403 : : }
404 : : }
405 : 0 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
406 : : }
407 : :
408 [ # # ]: 0 : for_each_possible_cpu(cpu)
409 [ # # ]: 0 : totqlen += rcu_get_n_cbs_cpu(cpu);
410 : 0 : pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n",
411 : : smp_processor_id(), (long)(jiffies - rcu_state.gp_start),
412 : : (long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
413 [ # # ]: 0 : if (ndetected) {
414 : 0 : rcu_dump_cpu_stacks();
415 : :
416 : : /* Complain about tasks blocking the grace period. */
417 [ # # ]: 0 : rcu_for_each_leaf_node(rnp)
418 : 0 : rcu_print_detail_task_stall_rnp(rnp);
419 : : } else {
420 [ # # ]: 0 : if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) {
421 : 0 : pr_err("INFO: Stall ended before state dump start\n");
422 : : } else {
423 : 0 : j = jiffies;
424 : 0 : gpa = READ_ONCE(rcu_state.gp_activity);
425 : 0 : pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
426 : : rcu_state.name, j - gpa, j, gpa,
427 : : READ_ONCE(jiffies_till_next_fqs),
428 : : rcu_get_root()->qsmask);
429 : : /* In this case, the current CPU might be at fault. */
430 : 0 : sched_show_task(current);
431 : : }
432 : : }
433 : : /* Rewrite if needed in case of slow consoles. */
434 [ # # ]: 0 : if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
435 [ # # ]: 0 : WRITE_ONCE(rcu_state.jiffies_stall,
436 : : jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
437 : :
438 : 0 : rcu_check_gp_kthread_starvation();
439 : :
440 [ # # ]: 0 : panic_on_rcu_stall();
441 : :
442 : 0 : rcu_force_quiescent_state(); /* Kick them all. */
443 : : }
444 : :
445 : 0 : static void print_cpu_stall(void)
446 : : {
447 : 0 : int cpu;
448 : 0 : unsigned long flags;
449 : 0 : struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
450 : 0 : struct rcu_node *rnp = rcu_get_root();
451 : 0 : long totqlen = 0;
452 : :
453 : : /* Kick and suppress, if so configured. */
454 : 0 : rcu_stall_kick_kthreads();
455 [ # # ]: 0 : if (rcu_cpu_stall_suppress)
456 : : return;
457 : :
458 : : /*
459 : : * OK, time to rat on ourselves...
460 : : * See Documentation/RCU/stallwarn.txt for info on how to debug
461 : : * RCU CPU stall warnings.
462 : : */
463 : 0 : pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name);
464 : 0 : raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
465 : 0 : print_cpu_stall_info(smp_processor_id());
466 : 0 : raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
467 [ # # ]: 0 : for_each_possible_cpu(cpu)
468 [ # # ]: 0 : totqlen += rcu_get_n_cbs_cpu(cpu);
469 : 0 : pr_cont("\t(t=%lu jiffies g=%ld q=%lu)\n",
470 : : jiffies - rcu_state.gp_start,
471 : : (long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
472 : :
473 : 0 : rcu_check_gp_kthread_starvation();
474 : :
475 : 0 : rcu_dump_cpu_stacks();
476 : :
477 : 0 : raw_spin_lock_irqsave_rcu_node(rnp, flags);
478 : : /* Rewrite if needed in case of slow consoles. */
479 [ # # ]: 0 : if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
480 [ # # ]: 0 : WRITE_ONCE(rcu_state.jiffies_stall,
481 : : jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
482 : 0 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
483 : :
484 [ # # ]: 0 : panic_on_rcu_stall();
485 : :
486 : : /*
487 : : * Attempt to revive the RCU machinery by forcing a context switch.
488 : : *
489 : : * A context switch would normally allow the RCU state machine to make
490 : : * progress and it could be we're stuck in kernel space without context
491 : : * switches for an entirely unreasonable amount of time.
492 : : */
493 : 0 : set_tsk_need_resched(current);
494 : 0 : set_preempt_need_resched();
495 : : }
496 : :
497 : : static void check_cpu_stall(struct rcu_data *rdp)
498 : : {
499 : : unsigned long gs1;
500 : : unsigned long gs2;
501 : : unsigned long gps;
502 : : unsigned long j;
503 : : unsigned long jn;
504 : : unsigned long js;
505 : : struct rcu_node *rnp;
506 : :
507 : : if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
508 : : !rcu_gp_in_progress())
509 : : return;
510 : : rcu_stall_kick_kthreads();
511 : : j = jiffies;
512 : :
513 : : /*
514 : : * Lots of memory barriers to reject false positives.
515 : : *
516 : : * The idea is to pick up rcu_state.gp_seq, then
517 : : * rcu_state.jiffies_stall, then rcu_state.gp_start, and finally
518 : : * another copy of rcu_state.gp_seq. These values are updated in
519 : : * the opposite order with memory barriers (or equivalent) during
520 : : * grace-period initialization and cleanup. Now, a false positive
521 : : * can occur if we get an new value of rcu_state.gp_start and a old
522 : : * value of rcu_state.jiffies_stall. But given the memory barriers,
523 : : * the only way that this can happen is if one grace period ends
524 : : * and another starts between these two fetches. This is detected
525 : : * by comparing the second fetch of rcu_state.gp_seq with the
526 : : * previous fetch from rcu_state.gp_seq.
527 : : *
528 : : * Given this check, comparisons of jiffies, rcu_state.jiffies_stall,
529 : : * and rcu_state.gp_start suffice to forestall false positives.
530 : : */
531 : : gs1 = READ_ONCE(rcu_state.gp_seq);
532 : : smp_rmb(); /* Pick up ->gp_seq first... */
533 : : js = READ_ONCE(rcu_state.jiffies_stall);
534 : : smp_rmb(); /* ...then ->jiffies_stall before the rest... */
535 : : gps = READ_ONCE(rcu_state.gp_start);
536 : : smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */
537 : : gs2 = READ_ONCE(rcu_state.gp_seq);
538 : : if (gs1 != gs2 ||
539 : : ULONG_CMP_LT(j, js) ||
540 : : ULONG_CMP_GE(gps, js))
541 : : return; /* No stall or GP completed since entering function. */
542 : : rnp = rdp->mynode;
543 : : jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
544 : : if (rcu_gp_in_progress() &&
545 : : (READ_ONCE(rnp->qsmask) & rdp->grpmask) &&
546 : : cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
547 : :
548 : : /* We haven't checked in, so go dump stack. */
549 : : print_cpu_stall();
550 : : if (rcu_cpu_stall_ftrace_dump)
551 : : rcu_ftrace_dump(DUMP_ALL);
552 : :
553 : : } else if (rcu_gp_in_progress() &&
554 : : ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) &&
555 : : cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
556 : :
557 : : /* They had a few time units to dump stack, so complain. */
558 : : print_other_cpu_stall(gs2);
559 : : if (rcu_cpu_stall_ftrace_dump)
560 : : rcu_ftrace_dump(DUMP_ALL);
561 : : }
562 : : }
563 : :
564 : : //////////////////////////////////////////////////////////////////////////////
565 : : //
566 : : // RCU forward-progress mechanisms, including of callback invocation.
567 : :
568 : :
569 : : /*
570 : : * Show the state of the grace-period kthreads.
571 : : */
572 : 0 : void show_rcu_gp_kthreads(void)
573 : : {
574 : 0 : int cpu;
575 : 0 : unsigned long j;
576 : 0 : unsigned long ja;
577 : 0 : unsigned long jr;
578 : 0 : unsigned long jw;
579 : 0 : struct rcu_data *rdp;
580 : 0 : struct rcu_node *rnp;
581 : :
582 : 0 : j = jiffies;
583 [ # # ]: 0 : ja = j - READ_ONCE(rcu_state.gp_activity);
584 : 0 : jr = j - READ_ONCE(rcu_state.gp_req_activity);
585 : 0 : jw = j - READ_ONCE(rcu_state.gp_wake_time);
586 [ # # # # ]: 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",
587 : : rcu_state.name, gp_state_getname(rcu_state.gp_state),
588 : : rcu_state.gp_state,
589 : : rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL,
590 : : ja, jr, jw, (long)READ_ONCE(rcu_state.gp_wake_seq),
591 : : (long)READ_ONCE(rcu_state.gp_seq),
592 : : (long)READ_ONCE(rcu_get_root()->gp_seq_needed),
593 : : READ_ONCE(rcu_state.gp_flags));
594 [ # # ]: 0 : rcu_for_each_node_breadth_first(rnp) {
595 [ # # ]: 0 : if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed))
596 : 0 : continue;
597 : 0 : pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n",
598 : : rnp->grplo, rnp->grphi, (long)rnp->gp_seq,
599 : : (long)rnp->gp_seq_needed);
600 [ # # ]: 0 : if (!rcu_is_leaf_node(rnp))
601 : 0 : continue;
602 [ # # ]: 0 : for_each_leaf_node_possible_cpu(rnp, cpu) {
603 : 0 : rdp = per_cpu_ptr(&rcu_data, cpu);
604 [ # # ]: 0 : if (rdp->gpwrap ||
605 [ # # ]: 0 : ULONG_CMP_GE(rcu_state.gp_seq,
606 : : rdp->gp_seq_needed))
607 : 0 : continue;
608 : 0 : pr_info("\tcpu %d ->gp_seq_needed %ld\n",
609 : : cpu, (long)rdp->gp_seq_needed);
610 : : }
611 : : }
612 [ # # ]: 0 : for_each_possible_cpu(cpu) {
613 : 0 : rdp = per_cpu_ptr(&rcu_data, cpu);
614 : 0 : if (rcu_segcblist_is_offloaded(&rdp->cblist))
615 : : show_rcu_nocb_state(rdp);
616 : : }
617 : : /* sched_show_task(rcu_state.gp_kthread); */
618 : 0 : }
619 : : EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
620 : :
621 : : /*
622 : : * This function checks for grace-period requests that fail to motivate
623 : : * RCU to come out of its idle mode.
624 : : */
625 : 247986 : static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
626 : : const unsigned long gpssdelay)
627 : : {
628 : 247986 : unsigned long flags;
629 : 247986 : unsigned long j;
630 : 247986 : struct rcu_node *rnp_root = rcu_get_root();
631 : 247986 : static atomic_t warned = ATOMIC_INIT(0);
632 : :
633 : 247986 : if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||
634 : : ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed))
635 : 247986 : return;
636 : : j = jiffies; /* Expensive access, and in common case don't get here. */
637 : : if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
638 : : time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
639 : : atomic_read(&warned))
640 : : return;
641 : :
642 : : raw_spin_lock_irqsave_rcu_node(rnp, flags);
643 : : j = jiffies;
644 : : if (rcu_gp_in_progress() ||
645 : : ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
646 : : time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
647 : : time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
648 : : atomic_read(&warned)) {
649 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
650 : : return;
651 : : }
652 : : /* Hold onto the leaf lock to make others see warned==1. */
653 : :
654 : : if (rnp_root != rnp)
655 : : raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
656 : : j = jiffies;
657 : : if (rcu_gp_in_progress() ||
658 : : ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
659 : : time_before(j, rcu_state.gp_req_activity + gpssdelay) ||
660 : : time_before(j, rcu_state.gp_activity + gpssdelay) ||
661 : : atomic_xchg(&warned, 1)) {
662 : : if (rnp_root != rnp)
663 : : /* irqs remain disabled. */
664 : : raw_spin_unlock_rcu_node(rnp_root);
665 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
666 : : return;
667 : : }
668 : : WARN_ON(1);
669 : : if (rnp_root != rnp)
670 : : raw_spin_unlock_rcu_node(rnp_root);
671 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
672 : : show_rcu_gp_kthreads();
673 : : }
674 : :
675 : : /*
676 : : * Do a forward-progress check for rcutorture. This is normally invoked
677 : : * due to an OOM event. The argument "j" gives the time period during
678 : : * which rcutorture would like progress to have been made.
679 : : */
680 : 0 : void rcu_fwd_progress_check(unsigned long j)
681 : : {
682 : 0 : unsigned long cbs;
683 : 0 : int cpu;
684 : 0 : unsigned long max_cbs = 0;
685 : 0 : int max_cpu = -1;
686 : 0 : struct rcu_data *rdp;
687 : :
688 [ # # ]: 0 : if (rcu_gp_in_progress()) {
689 : 0 : pr_info("%s: GP age %lu jiffies\n",
690 : : __func__, jiffies - rcu_state.gp_start);
691 : 0 : show_rcu_gp_kthreads();
692 : : } else {
693 : 0 : pr_info("%s: Last GP end %lu jiffies ago\n",
694 : : __func__, jiffies - rcu_state.gp_end);
695 : 0 : preempt_disable();
696 : 0 : rdp = this_cpu_ptr(&rcu_data);
697 : 0 : rcu_check_gp_start_stall(rdp->mynode, rdp, j);
698 : 0 : preempt_enable();
699 : : }
700 [ # # ]: 0 : for_each_possible_cpu(cpu) {
701 [ # # ]: 0 : cbs = rcu_get_n_cbs_cpu(cpu);
702 [ # # ]: 0 : if (!cbs)
703 : 0 : continue;
704 [ # # ]: 0 : if (max_cpu < 0)
705 : 0 : pr_info("%s: callbacks", __func__);
706 : 0 : pr_cont(" %d: %lu", cpu, cbs);
707 [ # # ]: 0 : if (cbs <= max_cbs)
708 : 0 : continue;
709 : : max_cbs = cbs;
710 : : max_cpu = cpu;
711 : : }
712 [ # # ]: 0 : if (max_cpu >= 0)
713 : 0 : pr_cont("\n");
714 : 0 : }
715 : : EXPORT_SYMBOL_GPL(rcu_fwd_progress_check);
716 : :
717 : : /* Commandeer a sysrq key to dump RCU's tree. */
718 : : static bool sysrq_rcu;
719 : : module_param(sysrq_rcu, bool, 0444);
720 : :
721 : : /* Dump grace-period-request information due to commandeered sysrq. */
722 : 0 : static void sysrq_show_rcu(int key)
723 : : {
724 : 0 : show_rcu_gp_kthreads();
725 : 0 : }
726 : :
727 : : static struct sysrq_key_op sysrq_rcudump_op = {
728 : : .handler = sysrq_show_rcu,
729 : : .help_msg = "show-rcu(y)",
730 : : .action_msg = "Show RCU tree",
731 : : .enable_mask = SYSRQ_ENABLE_DUMP,
732 : : };
733 : :
734 : 30 : static int __init rcu_sysrq_init(void)
735 : : {
736 [ - + ]: 30 : if (sysrq_rcu)
737 : 0 : return register_sysrq_key('y', &sysrq_rcudump_op);
738 : : return 0;
739 : : }
740 : : early_initcall(rcu_sysrq_init);
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