kernel/rcu/tree_stall.h

   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 int rcu_jiffies_till_stall_check(void)
  25 {
  26         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         if (till_stall_check < 3) {
  33                 WRITE_ONCE(rcu_cpu_stall_timeout, 3);
  34                 till_stall_check = 3;
  35         } else if (till_stall_check > 300) {
  36                 WRITE_ONCE(rcu_cpu_stall_timeout, 300);
  37                 till_stall_check = 300;
  38         }
  39         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 void rcu_sysrq_start(void)
  45 {
  46         if (!rcu_cpu_stall_suppress)
  47                 rcu_cpu_stall_suppress = 2;
  48 }
  49
  50 void rcu_sysrq_end(void)
  51 {
  52         if (rcu_cpu_stall_suppress == 2)
  53                 rcu_cpu_stall_suppress = 0;
  54 }
  55
  56 /* Don't print RCU CPU stall warnings during a kernel panic. */
  57 static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
  58 {
  59         rcu_cpu_stall_suppress = 1;
  60         return NOTIFY_DONE;
  61 }
  62
  63 static struct notifier_block rcu_panic_block = {
  64         .notifier_call = rcu_panic,
  65 };
  66
  67 static int __init check_cpu_stall_init(void)
  68 {
  69         atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
  70         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         if (sysctl_panic_on_rcu_stall)
  78                 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 void rcu_cpu_stall_reset(void)
  91 {
  92         WRITE_ONCE(rcu_state.jiffies_stall, jiffies + ULONG_MAX / 2);
  93 }
  94
  95 //////////////////////////////////////////////////////////////////////////////
  96 //
  97 // Interaction with RCU grace periods
  98
  99 /* Start of new grace period, so record stall time (and forcing times). */
 100 static void record_gp_stall_check_time(void)
 101 {
 102         unsigned long j = jiffies;
 103         unsigned long j1;
 104
 105         rcu_state.gp_start = j;
 106         j1 = rcu_jiffies_till_stall_check();
 107         /* Record ->gp_start before ->jiffies_stall. */
 108         smp_store_release(&rcu_state.jiffies_stall, j + j1); /* ^^^ */
 109         rcu_state.jiffies_resched = j + j1 / 2;
 110         rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs);
 111 }
 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         rdp->ticks_this_gp = 0;
 117         rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
 118         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 static void rcu_stall_kick_kthreads(void)
 126 {
 127         unsigned long j;
 128
 129         if (!rcu_kick_kthreads)
 130                 return;
 131         j = READ_ONCE(rcu_state.jiffies_kick_kthreads);
 132         if (time_after(jiffies, j) && rcu_state.gp_kthread &&
 133             (rcu_gp_in_progress() || READ_ONCE(rcu_state.gp_flags))) {
 134                 WARN_ONCE(1, "Kicking %s grace-period kthread\n",
 135                           rcu_state.name);
 136                 rcu_ftrace_dump(DUMP_ALL);
 137                 wake_up_process(rcu_state.gp_kthread);
 138                 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 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         rnp = rdp->mynode;
 154         raw_spin_lock_rcu_node(rnp);
 155         if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
 156                 rdp->rcu_iw_gp_seq = rnp->gp_seq;
 157                 rdp->rcu_iw_pending = false;
 158         }
 159         raw_spin_unlock_rcu_node(rnp);
 160 }
 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 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_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 static void rcu_dump_cpu_stacks(void)
 245 {
 246         int cpu;
 247         unsigned long flags;
 248         struct rcu_node *rnp;
 249
 250         rcu_for_each_leaf_node(rnp) {
 251                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
 252                 for_each_leaf_node_possible_cpu(rnp, cpu)
 253                         if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
 254                                 if (!trigger_single_cpu_backtrace(cpu))
 255                                         dump_cpu_task(cpu);
 256                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 257         }
 258 }
 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 static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
 274 {
 275         *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 static const char *gp_state_getname(short gs)
 296 {
 297         if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
 298                 return "???";
 299         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 static void print_cpu_stall_info(int cpu)
 314 {
 315         unsigned long delta;
 316         char fast_no_hz[72];
 317         struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
 318         char *ticks_title;
 319         unsigned long ticks_value;
 320
 321         /*
 322          * We could be printing a lot while holding a spinlock.  Avoid
 323          * triggering hard lockup.
 324          */
 325         touch_nmi_watchdog();
 326
 327         ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq);
 328         if (ticks_value) {
 329                 ticks_title = "GPs behind";
 330         } else {
 331                 ticks_title = "ticks this GP";
 332                 ticks_value = rdp->ticks_this_gp;
 333         }
 334         print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
 335         delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
 336         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 }
 351
 352 /* Complain about starvation of grace-period kthread.  */
 353 static void rcu_check_gp_kthread_starvation(void)
 354 {
 355         struct task_struct *gpk = rcu_state.gp_kthread;
 356         unsigned long j;
 357
 358         j = jiffies - READ_ONCE(rcu_state.gp_activity);
 359         if (j > 2 * HZ) {
 360                 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                 if (gpk) {
 367                         pr_err("RCU grace-period kthread stack dump:\n");
 368                         sched_show_task(gpk);
 369                         wake_up_process(gpk);
 370                 }
 371         }
 372 }
 373
 374 static void print_other_cpu_stall(unsigned long gp_seq)
 375 {
 376         int cpu;
 377         unsigned long flags;
 378         unsigned long gpa;
 379         unsigned long j;
 380         int ndetected = 0;
 381         struct rcu_node *rnp;
 382         long totqlen = 0;
 383
 384         /* Kick and suppress, if so configured. */
 385         rcu_stall_kick_kthreads();
 386         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         pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name);
 395         rcu_for_each_leaf_node(rnp) {
 396                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
 397                 ndetected += rcu_print_task_stall(rnp);
 398                 if (rnp->qsmask != 0) {
 399                         for_each_leaf_node_possible_cpu(rnp, cpu)
 400                                 if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
 401                                         print_cpu_stall_info(cpu);
 402                                         ndetected++;
 403                                 }
 404                 }
 405                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 406         }
 407
 408         for_each_possible_cpu(cpu)
 409                 totqlen += rcu_get_n_cbs_cpu(cpu);
 410         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         if (ndetected) {
 414                 rcu_dump_cpu_stacks();
 415
 416                 /* Complain about tasks blocking the grace period. */
 417                 rcu_for_each_leaf_node(rnp)
 418                         rcu_print_detail_task_stall_rnp(rnp);
 419         } else {
 420                 if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) {
 421                         pr_err("INFO: Stall ended before state dump start\n");
 422                 } else {
 423                         j = jiffies;
 424                         gpa = READ_ONCE(rcu_state.gp_activity);
 425                         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                         sched_show_task(current);
 431                 }
 432         }
 433         /* Rewrite if needed in case of slow consoles. */
 434         if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
 435                 WRITE_ONCE(rcu_state.jiffies_stall,
 436                            jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
 437
 438         rcu_check_gp_kthread_starvation();
 439
 440         panic_on_rcu_stall();
 441
 442         rcu_force_quiescent_state();  /* Kick them all. */
 443 }
 444
 445 static void print_cpu_stall(void)
 446 {
 447         int cpu;
 448         unsigned long flags;
 449         struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 450         struct rcu_node *rnp = rcu_get_root();
 451         long totqlen = 0;
 452
 453         /* Kick and suppress, if so configured. */
 454         rcu_stall_kick_kthreads();
 455         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         pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name);
 464         raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
 465         print_cpu_stall_info(smp_processor_id());
 466         raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
 467         for_each_possible_cpu(cpu)
 468                 totqlen += rcu_get_n_cbs_cpu(cpu);
 469         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         rcu_check_gp_kthread_starvation();
 474
 475         rcu_dump_cpu_stacks();
 476
 477         raw_spin_lock_irqsave_rcu_node(rnp, flags);
 478         /* Rewrite if needed in case of slow consoles. */
 479         if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
 480                 WRITE_ONCE(rcu_state.jiffies_stall,
 481                            jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
 482         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 483
 484         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         set_tsk_need_resched(current);
 494         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 void show_rcu_gp_kthreads(void)
 573 {
 574         int cpu;
 575         unsigned long j;
 576         unsigned long ja;
 577         unsigned long jr;
 578         unsigned long jw;
 579         struct rcu_data *rdp;
 580         struct rcu_node *rnp;
 581
 582         j = jiffies;
 583         ja = j - READ_ONCE(rcu_state.gp_activity);
 584         jr = j - READ_ONCE(rcu_state.gp_req_activity);
 585         jw = j - READ_ONCE(rcu_state.gp_wake_time);
 586         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         rcu_for_each_node_breadth_first(rnp) {
 595                 if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed))
 596                         continue;
 597                 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                 if (!rcu_is_leaf_node(rnp))
 601                         continue;
 602                 for_each_leaf_node_possible_cpu(rnp, cpu) {
 603                         rdp = per_cpu_ptr(&rcu_data, cpu);
 604                         if (rdp->gpwrap ||
 605                             ULONG_CMP_GE(rcu_state.gp_seq,
 606                                          rdp->gp_seq_needed))
 607                                 continue;
 608                         pr_info("\tcpu %d ->gp_seq_needed %ld\n",
 609                                 cpu, (long)rdp->gp_seq_needed);
 610                 }
 611         }
 612         for_each_possible_cpu(cpu) {
 613                 rdp = per_cpu_ptr(&rcu_data, cpu);
 614                 if (rcu_segcblist_is_offloaded(&rdp->cblist))
 615                         show_rcu_nocb_state(rdp);
 616         }
 617         /* sched_show_task(rcu_state.gp_kthread); */
 618 }
 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 static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
 626                                      const unsigned long gpssdelay)
 627 {
 628         unsigned long flags;
 629         unsigned long j;
 630         struct rcu_node *rnp_root = rcu_get_root();
 631         static atomic_t warned = ATOMIC_INIT(0);
 632
 633         if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||
 634             ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed))
 635                 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 void rcu_fwd_progress_check(unsigned long j)
 681 {
 682         unsigned long cbs;
 683         int cpu;
 684         unsigned long max_cbs = 0;
 685         int max_cpu = -1;
 686         struct rcu_data *rdp;
 687
 688         if (rcu_gp_in_progress()) {
 689                 pr_info("%s: GP age %lu jiffies\n",
 690                         __func__, jiffies - rcu_state.gp_start);
 691                 show_rcu_gp_kthreads();
 692         } else {
 693                 pr_info("%s: Last GP end %lu jiffies ago\n",
 694                         __func__, jiffies - rcu_state.gp_end);
 695                 preempt_disable();
 696                 rdp = this_cpu_ptr(&rcu_data);
 697                 rcu_check_gp_start_stall(rdp->mynode, rdp, j);
 698                 preempt_enable();
 699         }
 700         for_each_possible_cpu(cpu) {
 701                 cbs = rcu_get_n_cbs_cpu(cpu);
 702                 if (!cbs)
 703                         continue;
 704                 if (max_cpu < 0)
 705                         pr_info("%s: callbacks", __func__);
 706                 pr_cont(" %d: %lu", cpu, cbs);
 707                 if (cbs <= max_cbs)
 708                         continue;
 709                 max_cbs = cbs;
 710                 max_cpu = cpu;
 711         }
 712         if (max_cpu >= 0)
 713                 pr_cont("\n");
 714 }
 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 static void sysrq_show_rcu(int key)
 723 {
 724         show_rcu_gp_kthreads();
 725 }
 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 static int __init rcu_sysrq_init(void)
 735 {
 736         if (sysrq_rcu)
 737                 return register_sysrq_key('y', &sysrq_rcudump_op);
 738         return 0;
 739 }
 740 early_initcall(rcu_sysrq_init);