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 #include <linux/console.h> 11 #include <linux/kvm_para.h> 12 #include <linux/rcu_notifier.h> 13 #include <linux/smp.h> 14 15 ////////////////////////////////////////////////////////////////////////////// 16 // 17 // Controlling CPU stall warnings, including delay calculation. 18 19 /* panic() on RCU Stall sysctl. */ 20 int sysctl_panic_on_rcu_stall __read_mostly; 21 int sysctl_max_rcu_stall_to_panic __read_mostly; 22 23 #ifdef CONFIG_SYSFS 24 25 static unsigned int rcu_stall_count; 26 27 static ssize_t rcu_stall_count_show(struct kobject *kobj, struct kobj_attribute *attr, 28 char *page) 29 { 30 return sysfs_emit(page, "%u\n", rcu_stall_count); 31 } 32 33 static struct kobj_attribute rcu_stall_count_attr = __ATTR_RO(rcu_stall_count); 34 35 static __init int kernel_rcu_stall_sysfs_init(void) 36 { 37 sysfs_add_file_to_group(kernel_kobj, &rcu_stall_count_attr.attr, NULL); 38 return 0; 39 } 40 41 late_initcall(kernel_rcu_stall_sysfs_init); 42 43 #endif // CONFIG_SYSFS 44 45 #ifdef CONFIG_PROVE_RCU 46 #define RCU_STALL_DELAY_DELTA (5 * HZ) 47 #else 48 #define RCU_STALL_DELAY_DELTA 0 49 #endif 50 #define RCU_STALL_MIGHT_DIV 8 51 #define RCU_STALL_MIGHT_MIN (2 * HZ) 52 53 int rcu_exp_jiffies_till_stall_check(void) 54 { 55 int cpu_stall_timeout = READ_ONCE(rcu_exp_cpu_stall_timeout); 56 int exp_stall_delay_delta = 0; 57 int till_stall_check; 58 59 // Zero says to use rcu_cpu_stall_timeout, but in milliseconds. 60 if (!cpu_stall_timeout) 61 cpu_stall_timeout = jiffies_to_msecs(rcu_jiffies_till_stall_check()); 62 63 // Limit check must be consistent with the Kconfig limits for 64 // CONFIG_RCU_EXP_CPU_STALL_TIMEOUT, so check the allowed range. 65 // The minimum clamped value is "2UL", because at least one full 66 // tick has to be guaranteed. 67 till_stall_check = clamp(msecs_to_jiffies(cpu_stall_timeout), 2UL, 300UL * HZ); 68 69 if (cpu_stall_timeout && jiffies_to_msecs(till_stall_check) != cpu_stall_timeout) 70 WRITE_ONCE(rcu_exp_cpu_stall_timeout, jiffies_to_msecs(till_stall_check)); 71 72 #ifdef CONFIG_PROVE_RCU 73 /* Add extra ~25% out of till_stall_check. */ 74 exp_stall_delay_delta = ((till_stall_check * 25) / 100) + 1; 75 #endif 76 77 return till_stall_check + exp_stall_delay_delta; 78 } 79 EXPORT_SYMBOL_GPL(rcu_exp_jiffies_till_stall_check); 80 81 /* Limit-check stall timeouts specified at boottime and runtime. */ 82 int rcu_jiffies_till_stall_check(void) 83 { 84 int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout); 85 86 /* 87 * Limit check must be consistent with the Kconfig limits 88 * for CONFIG_RCU_CPU_STALL_TIMEOUT. 89 */ 90 if (till_stall_check < 3) { 91 WRITE_ONCE(rcu_cpu_stall_timeout, 3); 92 till_stall_check = 3; 93 } else if (till_stall_check > 300) { 94 WRITE_ONCE(rcu_cpu_stall_timeout, 300); 95 till_stall_check = 300; 96 } 97 return till_stall_check * HZ + RCU_STALL_DELAY_DELTA; 98 } 99 EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check); 100 101 /* Don't do RCU CPU stall warnings during long sysrq printouts. */ 102 void rcu_sysrq_start(void) 103 { 104 if (!rcu_cpu_stall_suppress) 105 rcu_cpu_stall_suppress = 2; 106 } 107 108 void rcu_sysrq_end(void) 109 { 110 if (rcu_cpu_stall_suppress == 2) 111 rcu_cpu_stall_suppress = 0; 112 } 113 114 /* Don't print RCU CPU stall warnings during a kernel panic. */ 115 static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr) 116 { 117 rcu_cpu_stall_suppress = 1; 118 return NOTIFY_DONE; 119 } 120 121 static struct notifier_block rcu_panic_block = { 122 .notifier_call = rcu_panic, 123 }; 124 125 static int __init check_cpu_stall_init(void) 126 { 127 atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block); 128 return 0; 129 } 130 early_initcall(check_cpu_stall_init); 131 132 /* If so specified via sysctl, panic, yielding cleaner stall-warning output. */ 133 static void panic_on_rcu_stall(void) 134 { 135 static int cpu_stall; 136 137 if (++cpu_stall < sysctl_max_rcu_stall_to_panic) 138 return; 139 140 if (sysctl_panic_on_rcu_stall) 141 panic("RCU Stall\n"); 142 } 143 144 /** 145 * rcu_cpu_stall_reset - restart stall-warning timeout for current grace period 146 * 147 * To perform the reset request from the caller, disable stall detection until 148 * 3 fqs loops have passed. This is required to ensure a fresh jiffies is 149 * loaded. It should be safe to do from the fqs loop as enough timer 150 * interrupts and context switches should have passed. 151 * 152 * The caller must disable hard irqs. 153 */ 154 void rcu_cpu_stall_reset(void) 155 { 156 WRITE_ONCE(rcu_state.nr_fqs_jiffies_stall, 3); 157 WRITE_ONCE(rcu_state.jiffies_stall, ULONG_MAX); 158 } 159 160 ////////////////////////////////////////////////////////////////////////////// 161 // 162 // Interaction with RCU grace periods 163 164 /* Start of new grace period, so record stall time (and forcing times). */ 165 static void record_gp_stall_check_time(void) 166 { 167 unsigned long j = jiffies; 168 unsigned long j1; 169 170 WRITE_ONCE(rcu_state.gp_start, j); 171 j1 = rcu_jiffies_till_stall_check(); 172 smp_mb(); // ->gp_start before ->jiffies_stall and caller's ->gp_seq. 173 WRITE_ONCE(rcu_state.nr_fqs_jiffies_stall, 0); 174 WRITE_ONCE(rcu_state.jiffies_stall, j + j1); 175 rcu_state.jiffies_resched = j + j1 / 2; 176 rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs); 177 } 178 179 /* Zero ->ticks_this_gp and snapshot the number of RCU softirq handlers. */ 180 static void zero_cpu_stall_ticks(struct rcu_data *rdp) 181 { 182 rdp->ticks_this_gp = 0; 183 rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id()); 184 WRITE_ONCE(rdp->last_fqs_resched, jiffies); 185 } 186 187 /* 188 * If too much time has passed in the current grace period, and if 189 * so configured, go kick the relevant kthreads. 190 */ 191 static void rcu_stall_kick_kthreads(void) 192 { 193 unsigned long j; 194 195 if (!READ_ONCE(rcu_kick_kthreads)) 196 return; 197 j = READ_ONCE(rcu_state.jiffies_kick_kthreads); 198 if (time_after(jiffies, j) && rcu_state.gp_kthread && 199 (rcu_gp_in_progress() || READ_ONCE(rcu_state.gp_flags))) { 200 WARN_ONCE(1, "Kicking %s grace-period kthread\n", 201 rcu_state.name); 202 rcu_ftrace_dump(DUMP_ALL); 203 wake_up_process(rcu_state.gp_kthread); 204 WRITE_ONCE(rcu_state.jiffies_kick_kthreads, j + HZ); 205 } 206 } 207 208 /* 209 * Handler for the irq_work request posted about halfway into the RCU CPU 210 * stall timeout, and used to detect excessive irq disabling. Set state 211 * appropriately, but just complain if there is unexpected state on entry. 212 */ 213 static void rcu_iw_handler(struct irq_work *iwp) 214 { 215 struct rcu_data *rdp; 216 struct rcu_node *rnp; 217 218 rdp = container_of(iwp, struct rcu_data, rcu_iw); 219 rnp = rdp->mynode; 220 raw_spin_lock_rcu_node(rnp); 221 if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) { 222 rdp->rcu_iw_gp_seq = rnp->gp_seq; 223 rdp->rcu_iw_pending = false; 224 } 225 raw_spin_unlock_rcu_node(rnp); 226 } 227 228 ////////////////////////////////////////////////////////////////////////////// 229 // 230 // Printing RCU CPU stall warnings 231 232 #ifdef CONFIG_PREEMPT_RCU 233 234 /* 235 * Dump detailed information for all tasks blocking the current RCU 236 * grace period on the specified rcu_node structure. 237 */ 238 static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) 239 { 240 unsigned long flags; 241 struct task_struct *t; 242 243 raw_spin_lock_irqsave_rcu_node(rnp, flags); 244 if (!rcu_preempt_blocked_readers_cgp(rnp)) { 245 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 246 return; 247 } 248 t = list_entry(rnp->gp_tasks->prev, 249 struct task_struct, rcu_node_entry); 250 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { 251 /* 252 * We could be printing a lot while holding a spinlock. 253 * Avoid triggering hard lockup. 254 */ 255 touch_nmi_watchdog(); 256 sched_show_task(t); 257 } 258 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 259 } 260 261 // Communicate task state back to the RCU CPU stall warning request. 262 struct rcu_stall_chk_rdr { 263 int nesting; 264 union rcu_special rs; 265 bool on_blkd_list; 266 }; 267 268 /* 269 * Report out the state of a not-running task that is stalling the 270 * current RCU grace period. 271 */ 272 static int check_slow_task(struct task_struct *t, void *arg) 273 { 274 struct rcu_stall_chk_rdr *rscrp = arg; 275 276 if (task_curr(t)) 277 return -EBUSY; // It is running, so decline to inspect it. 278 rscrp->nesting = t->rcu_read_lock_nesting; 279 rscrp->rs = t->rcu_read_unlock_special; 280 rscrp->on_blkd_list = !list_empty(&t->rcu_node_entry); 281 return 0; 282 } 283 284 /* 285 * Scan the current list of tasks blocked within RCU read-side critical 286 * sections, printing out the tid of each of the first few of them. 287 */ 288 static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags) 289 __releases(rnp->lock) 290 { 291 int i = 0; 292 int ndetected = 0; 293 struct rcu_stall_chk_rdr rscr; 294 struct task_struct *t; 295 struct task_struct *ts[8]; 296 297 lockdep_assert_irqs_disabled(); 298 if (!rcu_preempt_blocked_readers_cgp(rnp)) { 299 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 300 return 0; 301 } 302 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", 303 rnp->level, rnp->grplo, rnp->grphi); 304 t = list_entry(rnp->gp_tasks->prev, 305 struct task_struct, rcu_node_entry); 306 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { 307 get_task_struct(t); 308 ts[i++] = t; 309 if (i >= ARRAY_SIZE(ts)) 310 break; 311 } 312 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 313 while (i) { 314 t = ts[--i]; 315 if (task_call_func(t, check_slow_task, &rscr)) 316 pr_cont(" P%d", t->pid); 317 else 318 pr_cont(" P%d/%d:%c%c%c%c", 319 t->pid, rscr.nesting, 320 ".b"[rscr.rs.b.blocked], 321 ".q"[rscr.rs.b.need_qs], 322 ".e"[rscr.rs.b.exp_hint], 323 ".l"[rscr.on_blkd_list]); 324 lockdep_assert_irqs_disabled(); 325 put_task_struct(t); 326 ndetected++; 327 } 328 pr_cont("\n"); 329 return ndetected; 330 } 331 332 #else /* #ifdef CONFIG_PREEMPT_RCU */ 333 334 /* 335 * Because preemptible RCU does not exist, we never have to check for 336 * tasks blocked within RCU read-side critical sections. 337 */ 338 static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) 339 { 340 } 341 342 /* 343 * Because preemptible RCU does not exist, we never have to check for 344 * tasks blocked within RCU read-side critical sections. 345 */ 346 static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags) 347 __releases(rnp->lock) 348 { 349 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 350 return 0; 351 } 352 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 353 354 /* 355 * Dump stacks of all tasks running on stalled CPUs. First try using 356 * NMIs, but fall back to manual remote stack tracing on architectures 357 * that don't support NMI-based stack dumps. The NMI-triggered stack 358 * traces are more accurate because they are printed by the target CPU. 359 */ 360 static void rcu_dump_cpu_stacks(unsigned long gp_seq) 361 { 362 int cpu; 363 unsigned long flags; 364 struct rcu_node *rnp; 365 366 rcu_for_each_leaf_node(rnp) { 367 printk_deferred_enter(); 368 for_each_leaf_node_possible_cpu(rnp, cpu) { 369 if (gp_seq != data_race(rcu_state.gp_seq)) { 370 printk_deferred_exit(); 371 pr_err("INFO: Stall ended during stack backtracing.\n"); 372 return; 373 } 374 if (!(data_race(rnp->qsmask) & leaf_node_cpu_bit(rnp, cpu))) 375 continue; 376 raw_spin_lock_irqsave_rcu_node(rnp, flags); 377 if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) { 378 if (cpu_is_offline(cpu)) 379 pr_err("Offline CPU %d blocking current GP.\n", cpu); 380 else 381 dump_cpu_task(cpu); 382 } 383 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 384 } 385 printk_deferred_exit(); 386 } 387 } 388 389 static const char * const gp_state_names[] = { 390 [RCU_GP_IDLE] = "RCU_GP_IDLE", 391 [RCU_GP_WAIT_GPS] = "RCU_GP_WAIT_GPS", 392 [RCU_GP_DONE_GPS] = "RCU_GP_DONE_GPS", 393 [RCU_GP_ONOFF] = "RCU_GP_ONOFF", 394 [RCU_GP_INIT] = "RCU_GP_INIT", 395 [RCU_GP_WAIT_FQS] = "RCU_GP_WAIT_FQS", 396 [RCU_GP_DOING_FQS] = "RCU_GP_DOING_FQS", 397 [RCU_GP_CLEANUP] = "RCU_GP_CLEANUP", 398 [RCU_GP_CLEANED] = "RCU_GP_CLEANED", 399 }; 400 401 /* 402 * Convert a ->gp_state value to a character string. 403 */ 404 static const char *gp_state_getname(short gs) 405 { 406 if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names)) 407 return "???"; 408 return gp_state_names[gs]; 409 } 410 411 /* Is the RCU grace-period kthread being starved of CPU time? */ 412 static bool rcu_is_gp_kthread_starving(unsigned long *jp) 413 { 414 unsigned long j = jiffies - READ_ONCE(rcu_state.gp_activity); 415 416 if (jp) 417 *jp = j; 418 return j > 2 * HZ; 419 } 420 421 static bool rcu_is_rcuc_kthread_starving(struct rcu_data *rdp, unsigned long *jp) 422 { 423 int cpu; 424 struct task_struct *rcuc; 425 unsigned long j; 426 427 rcuc = rdp->rcu_cpu_kthread_task; 428 if (!rcuc) 429 return false; 430 431 cpu = task_cpu(rcuc); 432 if (cpu_is_offline(cpu) || idle_cpu(cpu)) 433 return false; 434 435 j = jiffies - READ_ONCE(rdp->rcuc_activity); 436 437 if (jp) 438 *jp = j; 439 return j > 2 * HZ; 440 } 441 442 static void print_cpu_stat_info(int cpu) 443 { 444 struct rcu_snap_record rsr, *rsrp; 445 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); 446 struct kernel_cpustat *kcsp = &kcpustat_cpu(cpu); 447 448 if (!rcu_cpu_stall_cputime) 449 return; 450 451 rsrp = &rdp->snap_record; 452 if (rsrp->gp_seq != rdp->gp_seq) 453 return; 454 455 rsr.cputime_irq = kcpustat_field(kcsp, CPUTIME_IRQ, cpu); 456 rsr.cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu); 457 rsr.cputime_system = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu); 458 459 pr_err("\t hardirqs softirqs csw/system\n"); 460 pr_err("\t number: %8lld %10d %12lld\n", 461 kstat_cpu_irqs_sum(cpu) + arch_irq_stat_cpu(cpu) - rsrp->nr_hardirqs, 462 kstat_cpu_softirqs_sum(cpu) - rsrp->nr_softirqs, 463 nr_context_switches_cpu(cpu) - rsrp->nr_csw); 464 pr_err("\tcputime: %8lld %10lld %12lld ==> %d(ms)\n", 465 div_u64(rsr.cputime_irq - rsrp->cputime_irq, NSEC_PER_MSEC), 466 div_u64(rsr.cputime_softirq - rsrp->cputime_softirq, NSEC_PER_MSEC), 467 div_u64(rsr.cputime_system - rsrp->cputime_system, NSEC_PER_MSEC), 468 jiffies_to_msecs(jiffies - rsrp->jiffies)); 469 } 470 471 /* 472 * Print out diagnostic information for the specified stalled CPU. 473 * 474 * If the specified CPU is aware of the current RCU grace period, then 475 * print the number of scheduling clock interrupts the CPU has taken 476 * during the time that it has been aware. Otherwise, print the number 477 * of RCU grace periods that this CPU is ignorant of, for example, "1" 478 * if the CPU was aware of the previous grace period. 479 * 480 * Also print out idle info. 481 */ 482 static void print_cpu_stall_info(int cpu) 483 { 484 unsigned long delta; 485 bool falsepositive; 486 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); 487 char *ticks_title; 488 unsigned long ticks_value; 489 bool rcuc_starved; 490 unsigned long j; 491 char buf[32]; 492 493 /* 494 * We could be printing a lot while holding a spinlock. Avoid 495 * triggering hard lockup. 496 */ 497 touch_nmi_watchdog(); 498 499 ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq); 500 if (ticks_value) { 501 ticks_title = "GPs behind"; 502 } else { 503 ticks_title = "ticks this GP"; 504 ticks_value = rdp->ticks_this_gp; 505 } 506 delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq); 507 falsepositive = rcu_is_gp_kthread_starving(NULL) && 508 rcu_watching_snap_in_eqs(ct_rcu_watching_cpu(cpu)); 509 rcuc_starved = rcu_is_rcuc_kthread_starving(rdp, &j); 510 if (rcuc_starved) 511 // Print signed value, as negative values indicate a probable bug. 512 snprintf(buf, sizeof(buf), " rcuc=%ld jiffies(starved)", j); 513 pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%04x/%ld/%#lx softirq=%u/%u fqs=%ld%s%s\n", 514 cpu, 515 "O."[!!cpu_online(cpu)], 516 "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)], 517 "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)], 518 !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' : 519 rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' : 520 "!."[!delta], 521 ticks_value, ticks_title, 522 ct_rcu_watching_cpu(cpu) & 0xffff, 523 ct_nesting_cpu(cpu), ct_nmi_nesting_cpu(cpu), 524 rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), 525 data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart, 526 rcuc_starved ? buf : "", 527 falsepositive ? " (false positive?)" : ""); 528 529 print_cpu_stat_info(cpu); 530 } 531 532 /* Complain about starvation of grace-period kthread. */ 533 static void rcu_check_gp_kthread_starvation(void) 534 { 535 int cpu; 536 struct task_struct *gpk = rcu_state.gp_kthread; 537 unsigned long j; 538 539 if (rcu_is_gp_kthread_starving(&j)) { 540 cpu = gpk ? task_cpu(gpk) : -1; 541 pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#x ->cpu=%d\n", 542 rcu_state.name, j, 543 (long)rcu_seq_current(&rcu_state.gp_seq), 544 data_race(READ_ONCE(rcu_state.gp_flags)), 545 gp_state_getname(rcu_state.gp_state), 546 data_race(READ_ONCE(rcu_state.gp_state)), 547 gpk ? data_race(READ_ONCE(gpk->__state)) : ~0, cpu); 548 if (gpk) { 549 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); 550 551 pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name); 552 pr_err("RCU grace-period kthread stack dump:\n"); 553 sched_show_task(gpk); 554 if (cpu_is_offline(cpu)) { 555 pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu); 556 } else if (!(data_race(READ_ONCE(rdp->mynode->qsmask)) & rdp->grpmask)) { 557 pr_err("Stack dump where RCU GP kthread last ran:\n"); 558 dump_cpu_task(cpu); 559 } 560 wake_up_process(gpk); 561 } 562 } 563 } 564 565 /* Complain about missing wakeups from expired fqs wait timer */ 566 static void rcu_check_gp_kthread_expired_fqs_timer(void) 567 { 568 struct task_struct *gpk = rcu_state.gp_kthread; 569 short gp_state; 570 unsigned long jiffies_fqs; 571 int cpu; 572 573 /* 574 * Order reads of .gp_state and .jiffies_force_qs. 575 * Matching smp_wmb() is present in rcu_gp_fqs_loop(). 576 */ 577 gp_state = smp_load_acquire(&rcu_state.gp_state); 578 jiffies_fqs = READ_ONCE(rcu_state.jiffies_force_qs); 579 580 if (gp_state == RCU_GP_WAIT_FQS && 581 time_after(jiffies, jiffies_fqs + RCU_STALL_MIGHT_MIN) && 582 gpk && !READ_ONCE(gpk->on_rq)) { 583 cpu = task_cpu(gpk); 584 pr_err("%s kthread timer wakeup didn't happen for %ld jiffies! g%ld f%#x %s(%d) ->state=%#x\n", 585 rcu_state.name, (jiffies - jiffies_fqs), 586 (long)rcu_seq_current(&rcu_state.gp_seq), 587 data_race(READ_ONCE(rcu_state.gp_flags)), // Diagnostic read 588 gp_state_getname(RCU_GP_WAIT_FQS), RCU_GP_WAIT_FQS, 589 data_race(READ_ONCE(gpk->__state))); 590 pr_err("\tPossible timer handling issue on cpu=%d timer-softirq=%u\n", 591 cpu, kstat_softirqs_cpu(TIMER_SOFTIRQ, cpu)); 592 } 593 } 594 595 static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) 596 { 597 int cpu; 598 unsigned long flags; 599 unsigned long gpa; 600 unsigned long j; 601 int ndetected = 0; 602 struct rcu_node *rnp; 603 long totqlen = 0; 604 605 lockdep_assert_irqs_disabled(); 606 607 /* Kick and suppress, if so configured. */ 608 rcu_stall_kick_kthreads(); 609 if (rcu_stall_is_suppressed()) 610 return; 611 612 nbcon_cpu_emergency_enter(); 613 614 /* 615 * OK, time to rat on our buddy... 616 * See Documentation/RCU/stallwarn.rst for info on how to debug 617 * RCU CPU stall warnings. 618 */ 619 trace_rcu_stall_warning(rcu_state.name, TPS("StallDetected")); 620 pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name); 621 rcu_for_each_leaf_node(rnp) { 622 raw_spin_lock_irqsave_rcu_node(rnp, flags); 623 if (rnp->qsmask != 0) { 624 for_each_leaf_node_possible_cpu(rnp, cpu) 625 if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) { 626 print_cpu_stall_info(cpu); 627 ndetected++; 628 } 629 } 630 ndetected += rcu_print_task_stall(rnp, flags); // Releases rnp->lock. 631 lockdep_assert_irqs_disabled(); 632 } 633 634 for_each_possible_cpu(cpu) 635 totqlen += rcu_get_n_cbs_cpu(cpu); 636 pr_err("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu ncpus=%d)\n", 637 smp_processor_id(), (long)(jiffies - gps), 638 (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, 639 data_race(rcu_state.n_online_cpus)); // Diagnostic read 640 if (ndetected) { 641 rcu_dump_cpu_stacks(gp_seq); 642 643 /* Complain about tasks blocking the grace period. */ 644 rcu_for_each_leaf_node(rnp) 645 rcu_print_detail_task_stall_rnp(rnp); 646 } else { 647 if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) { 648 pr_err("INFO: Stall ended before state dump start\n"); 649 } else { 650 j = jiffies; 651 gpa = data_race(READ_ONCE(rcu_state.gp_activity)); 652 pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n", 653 rcu_state.name, j - gpa, j, gpa, 654 data_race(READ_ONCE(jiffies_till_next_fqs)), 655 data_race(READ_ONCE(rcu_get_root()->qsmask))); 656 } 657 } 658 /* Rewrite if needed in case of slow consoles. */ 659 if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall))) 660 WRITE_ONCE(rcu_state.jiffies_stall, 661 jiffies + 3 * rcu_jiffies_till_stall_check() + 3); 662 663 rcu_check_gp_kthread_expired_fqs_timer(); 664 rcu_check_gp_kthread_starvation(); 665 666 nbcon_cpu_emergency_exit(); 667 668 panic_on_rcu_stall(); 669 670 rcu_force_quiescent_state(); /* Kick them all. */ 671 } 672 673 static void print_cpu_stall(unsigned long gp_seq, unsigned long gps) 674 { 675 int cpu; 676 unsigned long flags; 677 struct rcu_data *rdp = this_cpu_ptr(&rcu_data); 678 struct rcu_node *rnp = rcu_get_root(); 679 long totqlen = 0; 680 681 lockdep_assert_irqs_disabled(); 682 683 /* Kick and suppress, if so configured. */ 684 rcu_stall_kick_kthreads(); 685 if (rcu_stall_is_suppressed()) 686 return; 687 688 nbcon_cpu_emergency_enter(); 689 690 /* 691 * OK, time to rat on ourselves... 692 * See Documentation/RCU/stallwarn.rst for info on how to debug 693 * RCU CPU stall warnings. 694 */ 695 trace_rcu_stall_warning(rcu_state.name, TPS("SelfDetected")); 696 pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name); 697 raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags); 698 print_cpu_stall_info(smp_processor_id()); 699 raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags); 700 for_each_possible_cpu(cpu) 701 totqlen += rcu_get_n_cbs_cpu(cpu); 702 pr_err("\t(t=%lu jiffies g=%ld q=%lu ncpus=%d)\n", 703 jiffies - gps, 704 (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, 705 data_race(rcu_state.n_online_cpus)); // Diagnostic read 706 707 rcu_check_gp_kthread_expired_fqs_timer(); 708 rcu_check_gp_kthread_starvation(); 709 710 rcu_dump_cpu_stacks(gp_seq); 711 712 raw_spin_lock_irqsave_rcu_node(rnp, flags); 713 /* Rewrite if needed in case of slow consoles. */ 714 if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall))) 715 WRITE_ONCE(rcu_state.jiffies_stall, 716 jiffies + 3 * rcu_jiffies_till_stall_check() + 3); 717 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 718 719 nbcon_cpu_emergency_exit(); 720 721 panic_on_rcu_stall(); 722 723 /* 724 * Attempt to revive the RCU machinery by forcing a context switch. 725 * 726 * A context switch would normally allow the RCU state machine to make 727 * progress and it could be we're stuck in kernel space without context 728 * switches for an entirely unreasonable amount of time. 729 */ 730 set_tsk_need_resched(current); 731 set_preempt_need_resched(); 732 } 733 734 static bool csd_lock_suppress_rcu_stall; 735 module_param(csd_lock_suppress_rcu_stall, bool, 0644); 736 737 static void check_cpu_stall(struct rcu_data *rdp) 738 { 739 bool self_detected; 740 unsigned long gs1; 741 unsigned long gs2; 742 unsigned long gps; 743 unsigned long j; 744 unsigned long jn; 745 unsigned long js; 746 struct rcu_node *rnp; 747 748 lockdep_assert_irqs_disabled(); 749 if ((rcu_stall_is_suppressed() && !READ_ONCE(rcu_kick_kthreads)) || 750 !rcu_gp_in_progress()) 751 return; 752 rcu_stall_kick_kthreads(); 753 754 /* 755 * Check if it was requested (via rcu_cpu_stall_reset()) that the FQS 756 * loop has to set jiffies to ensure a non-stale jiffies value. This 757 * is required to have good jiffies value after coming out of long 758 * breaks of jiffies updates. Not doing so can cause false positives. 759 */ 760 if (READ_ONCE(rcu_state.nr_fqs_jiffies_stall) > 0) 761 return; 762 763 j = jiffies; 764 765 /* 766 * Lots of memory barriers to reject false positives. 767 * 768 * The idea is to pick up rcu_state.gp_seq, then 769 * rcu_state.jiffies_stall, then rcu_state.gp_start, and finally 770 * another copy of rcu_state.gp_seq. These values are updated in 771 * the opposite order with memory barriers (or equivalent) during 772 * grace-period initialization and cleanup. Now, a false positive 773 * can occur if we get an new value of rcu_state.gp_start and a old 774 * value of rcu_state.jiffies_stall. But given the memory barriers, 775 * the only way that this can happen is if one grace period ends 776 * and another starts between these two fetches. This is detected 777 * by comparing the second fetch of rcu_state.gp_seq with the 778 * previous fetch from rcu_state.gp_seq. 779 * 780 * Given this check, comparisons of jiffies, rcu_state.jiffies_stall, 781 * and rcu_state.gp_start suffice to forestall false positives. 782 */ 783 gs1 = READ_ONCE(rcu_state.gp_seq); 784 smp_rmb(); /* Pick up ->gp_seq first... */ 785 js = READ_ONCE(rcu_state.jiffies_stall); 786 smp_rmb(); /* ...then ->jiffies_stall before the rest... */ 787 gps = READ_ONCE(rcu_state.gp_start); 788 smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */ 789 gs2 = READ_ONCE(rcu_state.gp_seq); 790 if (gs1 != gs2 || 791 ULONG_CMP_LT(j, js) || 792 ULONG_CMP_GE(gps, js) || 793 !rcu_seq_state(gs2)) 794 return; /* No stall or GP completed since entering function. */ 795 rnp = rdp->mynode; 796 jn = jiffies + ULONG_MAX / 2; 797 self_detected = READ_ONCE(rnp->qsmask) & rdp->grpmask; 798 if (rcu_gp_in_progress() && 799 (self_detected || ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) && 800 cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) { 801 /* 802 * If a virtual machine is stopped by the host it can look to 803 * the watchdog like an RCU stall. Check to see if the host 804 * stopped the vm. 805 */ 806 if (kvm_check_and_clear_guest_paused()) 807 return; 808 809 #ifdef CONFIG_SYSFS 810 ++rcu_stall_count; 811 #endif 812 813 rcu_stall_notifier_call_chain(RCU_STALL_NOTIFY_NORM, (void *)j - gps); 814 if (READ_ONCE(csd_lock_suppress_rcu_stall) && csd_lock_is_stuck()) { 815 pr_err("INFO: %s detected stall, but suppressed full report due to a stuck CSD-lock.\n", rcu_state.name); 816 } else if (self_detected) { 817 /* We haven't checked in, so go dump stack. */ 818 print_cpu_stall(gs2, gps); 819 } else { 820 /* They had a few time units to dump stack, so complain. */ 821 print_other_cpu_stall(gs2, gps); 822 } 823 824 if (READ_ONCE(rcu_cpu_stall_ftrace_dump)) 825 rcu_ftrace_dump(DUMP_ALL); 826 827 if (READ_ONCE(rcu_state.jiffies_stall) == jn) { 828 jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3; 829 WRITE_ONCE(rcu_state.jiffies_stall, jn); 830 } 831 } 832 } 833 834 ////////////////////////////////////////////////////////////////////////////// 835 // 836 // RCU forward-progress mechanisms, including for callback invocation. 837 838 839 /* 840 * Check to see if a failure to end RCU priority inversion was due to 841 * a CPU not passing through a quiescent state. When this happens, there 842 * is nothing that RCU priority boosting can do to help, so we shouldn't 843 * count this as an RCU priority boosting failure. A return of true says 844 * RCU priority boosting is to blame, and false says otherwise. If false 845 * is returned, the first of the CPUs to blame is stored through cpup. 846 * If there was no CPU blocking the current grace period, but also nothing 847 * in need of being boosted, *cpup is set to -1. This can happen in case 848 * of vCPU preemption while the last CPU is reporting its quiscent state, 849 * for example. 850 * 851 * If cpup is NULL, then a lockless quick check is carried out, suitable 852 * for high-rate usage. On the other hand, if cpup is non-NULL, each 853 * rcu_node structure's ->lock is acquired, ruling out high-rate usage. 854 */ 855 bool rcu_check_boost_fail(unsigned long gp_state, int *cpup) 856 { 857 bool atb = false; 858 int cpu; 859 unsigned long flags; 860 struct rcu_node *rnp; 861 862 rcu_for_each_leaf_node(rnp) { 863 if (!cpup) { 864 if (data_race(READ_ONCE(rnp->qsmask))) { 865 return false; 866 } else { 867 if (READ_ONCE(rnp->gp_tasks)) 868 atb = true; 869 continue; 870 } 871 } 872 *cpup = -1; 873 raw_spin_lock_irqsave_rcu_node(rnp, flags); 874 if (rnp->gp_tasks) 875 atb = true; 876 if (!rnp->qsmask) { 877 // No CPUs without quiescent states for this rnp. 878 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 879 continue; 880 } 881 // Find the first holdout CPU. 882 for_each_leaf_node_possible_cpu(rnp, cpu) { 883 if (rnp->qsmask & (1UL << (cpu - rnp->grplo))) { 884 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 885 *cpup = cpu; 886 return false; 887 } 888 } 889 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 890 } 891 // Can't blame CPUs, so must blame RCU priority boosting. 892 return atb; 893 } 894 EXPORT_SYMBOL_GPL(rcu_check_boost_fail); 895 896 /* 897 * Show the state of the grace-period kthreads. 898 */ 899 void show_rcu_gp_kthreads(void) 900 { 901 unsigned long cbs = 0; 902 int cpu; 903 unsigned long j; 904 unsigned long ja; 905 unsigned long jr; 906 unsigned long js; 907 unsigned long jw; 908 struct rcu_data *rdp; 909 struct rcu_node *rnp; 910 struct task_struct *t = READ_ONCE(rcu_state.gp_kthread); 911 912 j = jiffies; 913 ja = j - data_race(READ_ONCE(rcu_state.gp_activity)); 914 jr = j - data_race(READ_ONCE(rcu_state.gp_req_activity)); 915 js = j - data_race(READ_ONCE(rcu_state.gp_start)); 916 jw = j - data_race(READ_ONCE(rcu_state.gp_wake_time)); 917 pr_info("%s: wait state: %s(%d) ->state: %#x ->rt_priority %u delta ->gp_start %lu ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_max %lu ->gp_flags %#x\n", 918 rcu_state.name, gp_state_getname(rcu_state.gp_state), 919 data_race(READ_ONCE(rcu_state.gp_state)), 920 t ? data_race(READ_ONCE(t->__state)) : 0x1ffff, t ? t->rt_priority : 0xffU, 921 js, ja, jr, jw, (long)data_race(READ_ONCE(rcu_state.gp_wake_seq)), 922 (long)data_race(READ_ONCE(rcu_state.gp_seq)), 923 (long)data_race(READ_ONCE(rcu_get_root()->gp_seq_needed)), 924 data_race(READ_ONCE(rcu_state.gp_max)), 925 data_race(READ_ONCE(rcu_state.gp_flags))); 926 rcu_for_each_node_breadth_first(rnp) { 927 if (ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq), READ_ONCE(rnp->gp_seq_needed)) && 928 !data_race(READ_ONCE(rnp->qsmask)) && !data_race(READ_ONCE(rnp->boost_tasks)) && 929 !data_race(READ_ONCE(rnp->exp_tasks)) && !data_race(READ_ONCE(rnp->gp_tasks))) 930 continue; 931 pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld ->qsmask %#lx %c%c%c%c ->n_boosts %ld\n", 932 rnp->grplo, rnp->grphi, 933 (long)data_race(READ_ONCE(rnp->gp_seq)), 934 (long)data_race(READ_ONCE(rnp->gp_seq_needed)), 935 data_race(READ_ONCE(rnp->qsmask)), 936 ".b"[!!data_race(READ_ONCE(rnp->boost_kthread_task))], 937 ".B"[!!data_race(READ_ONCE(rnp->boost_tasks))], 938 ".E"[!!data_race(READ_ONCE(rnp->exp_tasks))], 939 ".G"[!!data_race(READ_ONCE(rnp->gp_tasks))], 940 data_race(READ_ONCE(rnp->n_boosts))); 941 if (!rcu_is_leaf_node(rnp)) 942 continue; 943 for_each_leaf_node_possible_cpu(rnp, cpu) { 944 rdp = per_cpu_ptr(&rcu_data, cpu); 945 if (READ_ONCE(rdp->gpwrap) || 946 ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq), 947 READ_ONCE(rdp->gp_seq_needed))) 948 continue; 949 pr_info("\tcpu %d ->gp_seq_needed %ld\n", 950 cpu, (long)data_race(READ_ONCE(rdp->gp_seq_needed))); 951 } 952 } 953 for_each_possible_cpu(cpu) { 954 rdp = per_cpu_ptr(&rcu_data, cpu); 955 cbs += data_race(READ_ONCE(rdp->n_cbs_invoked)); 956 if (rcu_segcblist_is_offloaded(&rdp->cblist)) 957 show_rcu_nocb_state(rdp); 958 } 959 pr_info("RCU callbacks invoked since boot: %lu\n", cbs); 960 show_rcu_tasks_gp_kthreads(); 961 } 962 EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads); 963 964 /* 965 * This function checks for grace-period requests that fail to motivate 966 * RCU to come out of its idle mode. 967 */ 968 static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, 969 const unsigned long gpssdelay) 970 { 971 unsigned long flags; 972 unsigned long j; 973 struct rcu_node *rnp_root = rcu_get_root(); 974 static atomic_t warned = ATOMIC_INIT(0); 975 976 if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() || 977 ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq), 978 READ_ONCE(rnp_root->gp_seq_needed)) || 979 !smp_load_acquire(&rcu_state.gp_kthread)) // Get stable kthread. 980 return; 981 j = jiffies; /* Expensive access, and in common case don't get here. */ 982 if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) || 983 time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) || 984 atomic_read(&warned)) 985 return; 986 987 raw_spin_lock_irqsave_rcu_node(rnp, flags); 988 j = jiffies; 989 if (rcu_gp_in_progress() || 990 ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq), 991 READ_ONCE(rnp_root->gp_seq_needed)) || 992 time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) || 993 time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) || 994 atomic_read(&warned)) { 995 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 996 return; 997 } 998 /* Hold onto the leaf lock to make others see warned==1. */ 999 1000 if (rnp_root != rnp) 1001 raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */ 1002 j = jiffies; 1003 if (rcu_gp_in_progress() || 1004 ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq), 1005 READ_ONCE(rnp_root->gp_seq_needed)) || 1006 time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) || 1007 time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) || 1008 atomic_xchg(&warned, 1)) { 1009 if (rnp_root != rnp) 1010 /* irqs remain disabled. */ 1011 raw_spin_unlock_rcu_node(rnp_root); 1012 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 1013 return; 1014 } 1015 WARN_ON(1); 1016 if (rnp_root != rnp) 1017 raw_spin_unlock_rcu_node(rnp_root); 1018 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 1019 show_rcu_gp_kthreads(); 1020 } 1021 1022 /* 1023 * Do a forward-progress check for rcutorture. This is normally invoked 1024 * due to an OOM event. The argument "j" gives the time period during 1025 * which rcutorture would like progress to have been made. 1026 */ 1027 void rcu_fwd_progress_check(unsigned long j) 1028 { 1029 unsigned long cbs; 1030 int cpu; 1031 unsigned long max_cbs = 0; 1032 int max_cpu = -1; 1033 struct rcu_data *rdp; 1034 1035 if (rcu_gp_in_progress()) { 1036 pr_info("%s: GP age %lu jiffies\n", 1037 __func__, jiffies - data_race(READ_ONCE(rcu_state.gp_start))); 1038 show_rcu_gp_kthreads(); 1039 } else { 1040 pr_info("%s: Last GP end %lu jiffies ago\n", 1041 __func__, jiffies - data_race(READ_ONCE(rcu_state.gp_end))); 1042 preempt_disable(); 1043 rdp = this_cpu_ptr(&rcu_data); 1044 rcu_check_gp_start_stall(rdp->mynode, rdp, j); 1045 preempt_enable(); 1046 } 1047 for_each_possible_cpu(cpu) { 1048 cbs = rcu_get_n_cbs_cpu(cpu); 1049 if (!cbs) 1050 continue; 1051 if (max_cpu < 0) 1052 pr_info("%s: callbacks", __func__); 1053 pr_cont(" %d: %lu", cpu, cbs); 1054 if (cbs <= max_cbs) 1055 continue; 1056 max_cbs = cbs; 1057 max_cpu = cpu; 1058 } 1059 if (max_cpu >= 0) 1060 pr_cont("\n"); 1061 } 1062 EXPORT_SYMBOL_GPL(rcu_fwd_progress_check); 1063 1064 /* Commandeer a sysrq key to dump RCU's tree. */ 1065 static bool sysrq_rcu; 1066 module_param(sysrq_rcu, bool, 0444); 1067 1068 /* Dump grace-period-request information due to commandeered sysrq. */ 1069 static void sysrq_show_rcu(u8 key) 1070 { 1071 show_rcu_gp_kthreads(); 1072 } 1073 1074 static const struct sysrq_key_op sysrq_rcudump_op = { 1075 .handler = sysrq_show_rcu, 1076 .help_msg = "show-rcu(y)", 1077 .action_msg = "Show RCU tree", 1078 .enable_mask = SYSRQ_ENABLE_DUMP, 1079 }; 1080 1081 static int __init rcu_sysrq_init(void) 1082 { 1083 if (sysrq_rcu) 1084 return register_sysrq_key('y', &sysrq_rcudump_op); 1085 return 0; 1086 } 1087 early_initcall(rcu_sysrq_init); 1088 1089 #ifdef CONFIG_RCU_CPU_STALL_NOTIFIER 1090 1091 ////////////////////////////////////////////////////////////////////////////// 1092 // 1093 // RCU CPU stall-warning notifiers 1094 1095 static ATOMIC_NOTIFIER_HEAD(rcu_cpu_stall_notifier_list); 1096 1097 /** 1098 * rcu_stall_chain_notifier_register - Add an RCU CPU stall notifier 1099 * @n: Entry to add. 1100 * 1101 * Adds an RCU CPU stall notifier to an atomic notifier chain. 1102 * The @action passed to a notifier will be @RCU_STALL_NOTIFY_NORM or 1103 * friends. The @data will be the duration of the stalled grace period, 1104 * in jiffies, coerced to a void* pointer. 1105 * 1106 * Returns 0 on success, %-EEXIST on error. 1107 */ 1108 int rcu_stall_chain_notifier_register(struct notifier_block *n) 1109 { 1110 int rcsn = rcu_cpu_stall_notifiers; 1111 1112 WARN(1, "Adding %pS() to RCU stall notifier list (%s).\n", n->notifier_call, 1113 rcsn ? "possibly suppressing RCU CPU stall warnings" : "failed, so all is well"); 1114 if (rcsn) 1115 return atomic_notifier_chain_register(&rcu_cpu_stall_notifier_list, n); 1116 return -EEXIST; 1117 } 1118 EXPORT_SYMBOL_GPL(rcu_stall_chain_notifier_register); 1119 1120 /** 1121 * rcu_stall_chain_notifier_unregister - Remove an RCU CPU stall notifier 1122 * @n: Entry to add. 1123 * 1124 * Removes an RCU CPU stall notifier from an atomic notifier chain. 1125 * 1126 * Returns zero on success, %-ENOENT on failure. 1127 */ 1128 int rcu_stall_chain_notifier_unregister(struct notifier_block *n) 1129 { 1130 return atomic_notifier_chain_unregister(&rcu_cpu_stall_notifier_list, n); 1131 } 1132 EXPORT_SYMBOL_GPL(rcu_stall_chain_notifier_unregister); 1133 1134 /* 1135 * rcu_stall_notifier_call_chain - Call functions in an RCU CPU stall notifier chain 1136 * @val: Value passed unmodified to notifier function 1137 * @v: Pointer passed unmodified to notifier function 1138 * 1139 * Calls each function in the RCU CPU stall notifier chain in turn, which 1140 * is an atomic call chain. See atomic_notifier_call_chain() for more 1141 * information. 1142 * 1143 * This is for use within RCU, hence the omission of the extra asterisk 1144 * to indicate a non-kerneldoc format header comment. 1145 */ 1146 int rcu_stall_notifier_call_chain(unsigned long val, void *v) 1147 { 1148 return atomic_notifier_call_chain(&rcu_cpu_stall_notifier_list, val, v); 1149 } 1150 1151 #endif // #ifdef CONFIG_RCU_CPU_STALL_NOTIFIER 1152