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 #include <linux/kvm_para.h>
  11
  12 //////////////////////////////////////////////////////////////////////////////
  13 //
  14 // Controlling CPU stall warnings, including delay calculation.
  15
  16 /* panic() on RCU Stall sysctl. */
  17 int sysctl_panic_on_rcu_stall __read_mostly;
  18
  19 #ifdef CONFIG_PROVE_RCU
  20 #define RCU_STALL_DELAY_DELTA          (5 * HZ)
  21 #else
  22 #define RCU_STALL_DELAY_DELTA          0
  23 #endif
  24
  25 /* Limit-check stall timeouts specified at boottime and runtime. */
  26 int rcu_jiffies_till_stall_check(void)
  27 {
  28         int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout);
  29
  30         /*
  31          * Limit check must be consistent with the Kconfig limits
  32          * for CONFIG_RCU_CPU_STALL_TIMEOUT.
  33          */
  34         if (till_stall_check < 3) {
  35                 WRITE_ONCE(rcu_cpu_stall_timeout, 3);
  36                 till_stall_check = 3;
  37         } else if (till_stall_check > 300) {
  38                 WRITE_ONCE(rcu_cpu_stall_timeout, 300);
  39                 till_stall_check = 300;
  40         }
  41         return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
  42 }
  43 EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check);
  44
  45 /* Don't do RCU CPU stall warnings during long sysrq printouts. */
  46 void rcu_sysrq_start(void)
  47 {
  48         if (!rcu_cpu_stall_suppress)
  49                 rcu_cpu_stall_suppress = 2;
  50 }
  51
  52 void rcu_sysrq_end(void)
  53 {
  54         if (rcu_cpu_stall_suppress == 2)
  55                 rcu_cpu_stall_suppress = 0;
  56 }
  57
  58 /* Don't print RCU CPU stall warnings during a kernel panic. */
  59 static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
  60 {
  61         rcu_cpu_stall_suppress = 1;
  62         return NOTIFY_DONE;
  63 }
  64
  65 static struct notifier_block rcu_panic_block = {
  66         .notifier_call = rcu_panic,
  67 };
  68
  69 static int __init check_cpu_stall_init(void)
  70 {
  71         atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
  72         return 0;
  73 }
  74 early_initcall(check_cpu_stall_init);
  75
  76 /* If so specified via sysctl, panic, yielding cleaner stall-warning output. */
  77 static void panic_on_rcu_stall(void)
  78 {
  79         if (sysctl_panic_on_rcu_stall)
  80                 panic("RCU Stall\n");
  81 }
  82
  83 /**
  84  * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
  85  *
  86  * Set the stall-warning timeout way off into the future, thus preventing
  87  * any RCU CPU stall-warning messages from appearing in the current set of
  88  * RCU grace periods.
  89  *
  90  * The caller must disable hard irqs.
  91  */
  92 void rcu_cpu_stall_reset(void)
  93 {
  94         WRITE_ONCE(rcu_state.jiffies_stall, jiffies + ULONG_MAX / 2);
  95 }
  96
  97 //////////////////////////////////////////////////////////////////////////////
  98 //
  99 // Interaction with RCU grace periods
 100
 101 /* Start of new grace period, so record stall time (and forcing times). */
 102 static void record_gp_stall_check_time(void)
 103 {
 104         unsigned long j = jiffies;
 105         unsigned long j1;
 106
 107         rcu_state.gp_start = j;
 108         j1 = rcu_jiffies_till_stall_check();
 109         /* Record ->gp_start before ->jiffies_stall. */
 110         smp_store_release(&rcu_state.jiffies_stall, j + j1); /* ^^^ */
 111         rcu_state.jiffies_resched = j + j1 / 2;
 112         rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs);
 113 }
 114
 115 /* Zero ->ticks_this_gp and snapshot the number of RCU softirq handlers. */
 116 static void zero_cpu_stall_ticks(struct rcu_data *rdp)
 117 {
 118         rdp->ticks_this_gp = 0;
 119         rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
 120         WRITE_ONCE(rdp->last_fqs_resched, jiffies);
 121 }
 122
 123 /*
 124  * If too much time has passed in the current grace period, and if
 125  * so configured, go kick the relevant kthreads.
 126  */
 127 static void rcu_stall_kick_kthreads(void)
 128 {
 129         unsigned long j;
 130
 131         if (!rcu_kick_kthreads)
 132                 return;
 133         j = READ_ONCE(rcu_state.jiffies_kick_kthreads);
 134         if (time_after(jiffies, j) && rcu_state.gp_kthread &&
 135             (rcu_gp_in_progress() || READ_ONCE(rcu_state.gp_flags))) {
 136                 WARN_ONCE(1, "Kicking %s grace-period kthread\n",
 137                           rcu_state.name);
 138                 rcu_ftrace_dump(DUMP_ALL);
 139                 wake_up_process(rcu_state.gp_kthread);
 140                 WRITE_ONCE(rcu_state.jiffies_kick_kthreads, j + HZ);
 141         }
 142 }
 143
 144 /*
 145  * Handler for the irq_work request posted about halfway into the RCU CPU
 146  * stall timeout, and used to detect excessive irq disabling.  Set state
 147  * appropriately, but just complain if there is unexpected state on entry.
 148  */
 149 static void rcu_iw_handler(struct irq_work *iwp)
 150 {
 151         struct rcu_data *rdp;
 152         struct rcu_node *rnp;
 153
 154         rdp = container_of(iwp, struct rcu_data, rcu_iw);
 155         rnp = rdp->mynode;
 156         raw_spin_lock_rcu_node(rnp);
 157         if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
 158                 rdp->rcu_iw_gp_seq = rnp->gp_seq;
 159                 rdp->rcu_iw_pending = false;
 160         }
 161         raw_spin_unlock_rcu_node(rnp);
 162 }
 163
 164 //////////////////////////////////////////////////////////////////////////////
 165 //
 166 // Printing RCU CPU stall warnings
 167
 168 #ifdef CONFIG_PREEMPTION
 169
 170 /*
 171  * Dump detailed information for all tasks blocking the current RCU
 172  * grace period on the specified rcu_node structure.
 173  */
 174 static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
 175 {
 176         unsigned long flags;
 177         struct task_struct *t;
 178
 179         raw_spin_lock_irqsave_rcu_node(rnp, flags);
 180         if (!rcu_preempt_blocked_readers_cgp(rnp)) {
 181                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 182                 return;
 183         }
 184         t = list_entry(rnp->gp_tasks->prev,
 185                        struct task_struct, rcu_node_entry);
 186         list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
 187                 /*
 188                  * We could be printing a lot while holding a spinlock.
 189                  * Avoid triggering hard lockup.
 190                  */
 191                 touch_nmi_watchdog();
 192                 sched_show_task(t);
 193         }
 194         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 195 }
 196
 197 /*
 198  * Scan the current list of tasks blocked within RCU read-side critical
 199  * sections, printing out the tid of each.
 200  */
 201 static int rcu_print_task_stall(struct rcu_node *rnp)
 202 {
 203         struct task_struct *t;
 204         int ndetected = 0;
 205
 206         if (!rcu_preempt_blocked_readers_cgp(rnp))
 207                 return 0;
 208         pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
 209                rnp->level, rnp->grplo, rnp->grphi);
 210         t = list_entry(rnp->gp_tasks->prev,
 211                        struct task_struct, rcu_node_entry);
 212         list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
 213                 pr_cont(" P%d", t->pid);
 214                 ndetected++;
 215         }
 216         pr_cont("\n");
 217         return ndetected;
 218 }
 219
 220 #else /* #ifdef CONFIG_PREEMPTION */
 221
 222 /*
 223  * Because preemptible RCU does not exist, we never have to check for
 224  * tasks blocked within RCU read-side critical sections.
 225  */
 226 static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
 227 {
 228 }
 229
 230 /*
 231  * Because preemptible RCU does not exist, we never have to check for
 232  * tasks blocked within RCU read-side critical sections.
 233  */
 234 static int rcu_print_task_stall(struct rcu_node *rnp)
 235 {
 236         return 0;
 237 }
 238 #endif /* #else #ifdef CONFIG_PREEMPTION */
 239
 240 /*
 241  * Dump stacks of all tasks running on stalled CPUs.  First try using
 242  * NMIs, but fall back to manual remote stack tracing on architectures
 243  * that don't support NMI-based stack dumps.  The NMI-triggered stack
 244  * traces are more accurate because they are printed by the target CPU.
 245  */
 246 static void rcu_dump_cpu_stacks(void)
 247 {
 248         int cpu;
 249         unsigned long flags;
 250         struct rcu_node *rnp;
 251
 252         rcu_for_each_leaf_node(rnp) {
 253                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
 254                 for_each_leaf_node_possible_cpu(rnp, cpu)
 255                         if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
 256                                 if (!trigger_single_cpu_backtrace(cpu))
 257                                         dump_cpu_task(cpu);
 258                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 259         }
 260 }
 261
 262 #ifdef CONFIG_RCU_FAST_NO_HZ
 263
 264 static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
 265 {
 266         struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
 267
 268         sprintf(cp, "last_accelerate: %04lx/%04lx, Nonlazy posted: %c%c%c",
 269                 rdp->last_accelerate & 0xffff, jiffies & 0xffff,
 270                 ".l"[rdp->all_lazy],
 271                 ".L"[!rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)],
 272                 ".D"[!!rdp->tick_nohz_enabled_snap]);
 273 }
 274
 275 #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
 276
 277 static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
 278 {
 279         *cp = '\0';
 280 }
 281
 282 #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
 283
 284 /*
 285  * Print out diagnostic information for the specified stalled CPU.
 286  *
 287  * If the specified CPU is aware of the current RCU grace period, then
 288  * print the number of scheduling clock interrupts the CPU has taken
 289  * during the time that it has been aware.  Otherwise, print the number
 290  * of RCU grace periods that this CPU is ignorant of, for example, "1"
 291  * if the CPU was aware of the previous grace period.
 292  *
 293  * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
 294  */
 295 static void print_cpu_stall_info(int cpu)
 296 {
 297         unsigned long delta;
 298         char fast_no_hz[72];
 299         struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
 300         char *ticks_title;
 301         unsigned long ticks_value;
 302
 303         /*
 304          * We could be printing a lot while holding a spinlock.  Avoid
 305          * triggering hard lockup.
 306          */
 307         touch_nmi_watchdog();
 308
 309         ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq);
 310         if (ticks_value) {
 311                 ticks_title = "GPs behind";
 312         } else {
 313                 ticks_title = "ticks this GP";
 314                 ticks_value = rdp->ticks_this_gp;
 315         }
 316         print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
 317         delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
 318         pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n",
 319                cpu,
 320                "O."[!!cpu_online(cpu)],
 321                "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
 322                "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
 323                !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
 324                         rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
 325                                 "!."[!delta],
 326                ticks_value, ticks_title,
 327                rcu_dynticks_snap(rdp) & 0xfff,
 328                rdp->dynticks_nesting, rdp->dynticks_nmi_nesting,
 329                rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
 330                READ_ONCE(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,
 331                fast_no_hz);
 332 }
 333
 334 /* Complain about starvation of grace-period kthread.  */
 335 static void rcu_check_gp_kthread_starvation(void)
 336 {
 337         struct task_struct *gpk = rcu_state.gp_kthread;
 338         unsigned long j;
 339
 340         j = jiffies - READ_ONCE(rcu_state.gp_activity);
 341         if (j > 2 * HZ) {
 342                 pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
 343                        rcu_state.name, j,
 344                        (long)rcu_seq_current(&rcu_state.gp_seq),
 345                        READ_ONCE(rcu_state.gp_flags),
 346                        gp_state_getname(rcu_state.gp_state), rcu_state.gp_state,
 347                        gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1);
 348                 if (gpk) {
 349                         pr_err("RCU grace-period kthread stack dump:\n");
 350                         sched_show_task(gpk);
 351                         wake_up_process(gpk);
 352                 }
 353         }
 354 }
 355
 356 static void print_other_cpu_stall(unsigned long gp_seq)
 357 {
 358         int cpu;
 359         unsigned long flags;
 360         unsigned long gpa;
 361         unsigned long j;
 362         int ndetected = 0;
 363         struct rcu_node *rnp;
 364         long totqlen = 0;
 365
 366         /* Kick and suppress, if so configured. */
 367         rcu_stall_kick_kthreads();
 368         if (rcu_cpu_stall_suppress)
 369                 return;
 370
 371         /*
 372          * OK, time to rat on our buddy...
 373          * See Documentation/RCU/stallwarn.txt for info on how to debug
 374          * RCU CPU stall warnings.
 375          */
 376         pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name);
 377         rcu_for_each_leaf_node(rnp) {
 378                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
 379                 ndetected += rcu_print_task_stall(rnp);
 380                 if (rnp->qsmask != 0) {
 381                         for_each_leaf_node_possible_cpu(rnp, cpu)
 382                                 if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
 383                                         print_cpu_stall_info(cpu);
 384                                         ndetected++;
 385                                 }
 386                 }
 387                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 388         }
 389
 390         for_each_possible_cpu(cpu)
 391                 totqlen += rcu_get_n_cbs_cpu(cpu);
 392         pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n",
 393                smp_processor_id(), (long)(jiffies - rcu_state.gp_start),
 394                (long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
 395         if (ndetected) {
 396                 rcu_dump_cpu_stacks();
 397
 398                 /* Complain about tasks blocking the grace period. */
 399                 rcu_for_each_leaf_node(rnp)
 400                         rcu_print_detail_task_stall_rnp(rnp);
 401         } else {
 402                 if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) {
 403                         pr_err("INFO: Stall ended before state dump start\n");
 404                 } else {
 405                         j = jiffies;
 406                         gpa = READ_ONCE(rcu_state.gp_activity);
 407                         pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
 408                                rcu_state.name, j - gpa, j, gpa,
 409                                READ_ONCE(jiffies_till_next_fqs),
 410                                rcu_get_root()->qsmask);
 411                         /* In this case, the current CPU might be at fault. */
 412                         sched_show_task(current);
 413                 }
 414         }
 415         /* Rewrite if needed in case of slow consoles. */
 416         if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
 417                 WRITE_ONCE(rcu_state.jiffies_stall,
 418                            jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
 419
 420         rcu_check_gp_kthread_starvation();
 421
 422         panic_on_rcu_stall();
 423
 424         rcu_force_quiescent_state();  /* Kick them all. */
 425 }
 426
 427 static void print_cpu_stall(void)
 428 {
 429         int cpu;
 430         unsigned long flags;
 431         struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 432         struct rcu_node *rnp = rcu_get_root();
 433         long totqlen = 0;
 434
 435         /* Kick and suppress, if so configured. */
 436         rcu_stall_kick_kthreads();
 437         if (rcu_cpu_stall_suppress)
 438                 return;
 439
 440         /*
 441          * OK, time to rat on ourselves...
 442          * See Documentation/RCU/stallwarn.txt for info on how to debug
 443          * RCU CPU stall warnings.
 444          */
 445         pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name);
 446         raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
 447         print_cpu_stall_info(smp_processor_id());
 448         raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
 449         for_each_possible_cpu(cpu)
 450                 totqlen += rcu_get_n_cbs_cpu(cpu);
 451         pr_cont("\t(t=%lu jiffies g=%ld q=%lu)\n",
 452                 jiffies - rcu_state.gp_start,
 453                 (long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
 454
 455         rcu_check_gp_kthread_starvation();
 456
 457         rcu_dump_cpu_stacks();
 458
 459         raw_spin_lock_irqsave_rcu_node(rnp, flags);
 460         /* Rewrite if needed in case of slow consoles. */
 461         if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
 462                 WRITE_ONCE(rcu_state.jiffies_stall,
 463                            jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
 464         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 465
 466         panic_on_rcu_stall();
 467
 468         /*
 469          * Attempt to revive the RCU machinery by forcing a context switch.
 470          *
 471          * A context switch would normally allow the RCU state machine to make
 472          * progress and it could be we're stuck in kernel space without context
 473          * switches for an entirely unreasonable amount of time.
 474          */
 475         set_tsk_need_resched(current);
 476         set_preempt_need_resched();
 477 }
 478
 479 static void check_cpu_stall(struct rcu_data *rdp)
 480 {
 481         unsigned long gs1;
 482         unsigned long gs2;
 483         unsigned long gps;
 484         unsigned long j;
 485         unsigned long jn;
 486         unsigned long js;
 487         struct rcu_node *rnp;
 488
 489         if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
 490             !rcu_gp_in_progress())
 491                 return;
 492         rcu_stall_kick_kthreads();
 493         j = jiffies;
 494
 495         /*
 496          * Lots of memory barriers to reject false positives.
 497          *
 498          * The idea is to pick up rcu_state.gp_seq, then
 499          * rcu_state.jiffies_stall, then rcu_state.gp_start, and finally
 500          * another copy of rcu_state.gp_seq.  These values are updated in
 501          * the opposite order with memory barriers (or equivalent) during
 502          * grace-period initialization and cleanup.  Now, a false positive
 503          * can occur if we get an new value of rcu_state.gp_start and a old
 504          * value of rcu_state.jiffies_stall.  But given the memory barriers,
 505          * the only way that this can happen is if one grace period ends
 506          * and another starts between these two fetches.  This is detected
 507          * by comparing the second fetch of rcu_state.gp_seq with the
 508          * previous fetch from rcu_state.gp_seq.
 509          *
 510          * Given this check, comparisons of jiffies, rcu_state.jiffies_stall,
 511          * and rcu_state.gp_start suffice to forestall false positives.
 512          */
 513         gs1 = READ_ONCE(rcu_state.gp_seq);
 514         smp_rmb(); /* Pick up ->gp_seq first... */
 515         js = READ_ONCE(rcu_state.jiffies_stall);
 516         smp_rmb(); /* ...then ->jiffies_stall before the rest... */
 517         gps = READ_ONCE(rcu_state.gp_start);
 518         smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */
 519         gs2 = READ_ONCE(rcu_state.gp_seq);
 520         if (gs1 != gs2 ||
 521             ULONG_CMP_LT(j, js) ||
 522             ULONG_CMP_GE(gps, js))
 523                 return; /* No stall or GP completed since entering function. */
 524         rnp = rdp->mynode;
 525         jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
 526         if (rcu_gp_in_progress() &&
 527             (READ_ONCE(rnp->qsmask) & rdp->grpmask) &&
 528             cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
 529
 530                 /*
 531                  * If a virtual machine is stopped by the host it can look to
 532                  * the watchdog like an RCU stall. Check to see if the host
 533                  * stopped the vm.
 534                  */
 535                 if (kvm_check_and_clear_guest_paused())
 536                         return;
 537
 538                 /* We haven't checked in, so go dump stack. */
 539                 print_cpu_stall();
 540                 if (rcu_cpu_stall_ftrace_dump)
 541                         rcu_ftrace_dump(DUMP_ALL);
 542
 543         } else if (rcu_gp_in_progress() &&
 544                    ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) &&
 545                    cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
 546
 547                 /*
 548                  * If a virtual machine is stopped by the host it can look to
 549                  * the watchdog like an RCU stall. Check to see if the host
 550                  * stopped the vm.
 551                  */
 552                 if (kvm_check_and_clear_guest_paused())
 553                         return;
 554
 555                 /* They had a few time units to dump stack, so complain. */
 556                 print_other_cpu_stall(gs2);
 557                 if (rcu_cpu_stall_ftrace_dump)
 558                         rcu_ftrace_dump(DUMP_ALL);
 559         }
 560 }
 561
 562 //////////////////////////////////////////////////////////////////////////////
 563 //
 564 // RCU forward-progress mechanisms, including of callback invocation.
 565
 566
 567 /*
 568  * Show the state of the grace-period kthreads.
 569  */
 570 void show_rcu_gp_kthreads(void)
 571 {
 572         int cpu;
 573         unsigned long j;
 574         unsigned long ja;
 575         unsigned long jr;
 576         unsigned long jw;
 577         struct rcu_data *rdp;
 578         struct rcu_node *rnp;
 579
 580         j = jiffies;
 581         ja = j - READ_ONCE(rcu_state.gp_activity);
 582         jr = j - READ_ONCE(rcu_state.gp_req_activity);
 583         jw = j - READ_ONCE(rcu_state.gp_wake_time);
 584         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",
 585                 rcu_state.name, gp_state_getname(rcu_state.gp_state),
 586                 rcu_state.gp_state,
 587                 rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL,
 588                 ja, jr, jw, (long)READ_ONCE(rcu_state.gp_wake_seq),
 589                 (long)READ_ONCE(rcu_state.gp_seq),
 590                 (long)READ_ONCE(rcu_get_root()->gp_seq_needed),
 591                 READ_ONCE(rcu_state.gp_flags));
 592         rcu_for_each_node_breadth_first(rnp) {
 593                 if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed))
 594                         continue;
 595                 pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n",
 596                         rnp->grplo, rnp->grphi, (long)rnp->gp_seq,
 597                         (long)rnp->gp_seq_needed);
 598                 if (!rcu_is_leaf_node(rnp))
 599                         continue;
 600                 for_each_leaf_node_possible_cpu(rnp, cpu) {
 601                         rdp = per_cpu_ptr(&rcu_data, cpu);
 602                         if (rdp->gpwrap ||
 603                             ULONG_CMP_GE(rcu_state.gp_seq,
 604                                          rdp->gp_seq_needed))
 605                                 continue;
 606                         pr_info("\tcpu %d ->gp_seq_needed %ld\n",
 607                                 cpu, (long)rdp->gp_seq_needed);
 608                 }
 609         }
 610         for_each_possible_cpu(cpu) {
 611                 rdp = per_cpu_ptr(&rcu_data, cpu);
 612                 if (rcu_segcblist_is_offloaded(&rdp->cblist))
 613                         show_rcu_nocb_state(rdp);
 614         }
 615         /* sched_show_task(rcu_state.gp_kthread); */
 616 }
 617 EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
 618
 619 /*
 620  * This function checks for grace-period requests that fail to motivate
 621  * RCU to come out of its idle mode.
 622  */
 623 static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
 624                                      const unsigned long gpssdelay)
 625 {
 626         unsigned long flags;
 627         unsigned long j;
 628         struct rcu_node *rnp_root = rcu_get_root();
 629         static atomic_t warned = ATOMIC_INIT(0);
 630
 631         if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||
 632             ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed))
 633                 return;
 634         j = jiffies; /* Expensive access, and in common case don't get here. */
 635         if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
 636             time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
 637             atomic_read(&warned))
 638                 return;
 639
 640         raw_spin_lock_irqsave_rcu_node(rnp, flags);
 641         j = jiffies;
 642         if (rcu_gp_in_progress() ||
 643             ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
 644             time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
 645             time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
 646             atomic_read(&warned)) {
 647                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 648                 return;
 649         }
 650         /* Hold onto the leaf lock to make others see warned==1. */
 651
 652         if (rnp_root != rnp)
 653                 raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
 654         j = jiffies;
 655         if (rcu_gp_in_progress() ||
 656             ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
 657             time_before(j, rcu_state.gp_req_activity + gpssdelay) ||
 658             time_before(j, rcu_state.gp_activity + gpssdelay) ||
 659             atomic_xchg(&warned, 1)) {
 660                 if (rnp_root != rnp)
 661                         /* irqs remain disabled. */
 662                         raw_spin_unlock_rcu_node(rnp_root);
 663                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 664                 return;
 665         }
 666         WARN_ON(1);
 667         if (rnp_root != rnp)
 668                 raw_spin_unlock_rcu_node(rnp_root);
 669         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 670         show_rcu_gp_kthreads();
 671 }
 672
 673 /*
 674  * Do a forward-progress check for rcutorture.  This is normally invoked
 675  * due to an OOM event.  The argument "j" gives the time period during
 676  * which rcutorture would like progress to have been made.
 677  */
 678 void rcu_fwd_progress_check(unsigned long j)
 679 {
 680         unsigned long cbs;
 681         int cpu;
 682         unsigned long max_cbs = 0;
 683         int max_cpu = -1;
 684         struct rcu_data *rdp;
 685
 686         if (rcu_gp_in_progress()) {
 687                 pr_info("%s: GP age %lu jiffies\n",
 688                         __func__, jiffies - rcu_state.gp_start);
 689                 show_rcu_gp_kthreads();
 690         } else {
 691                 pr_info("%s: Last GP end %lu jiffies ago\n",
 692                         __func__, jiffies - rcu_state.gp_end);
 693                 preempt_disable();
 694                 rdp = this_cpu_ptr(&rcu_data);
 695                 rcu_check_gp_start_stall(rdp->mynode, rdp, j);
 696                 preempt_enable();
 697         }
 698         for_each_possible_cpu(cpu) {
 699                 cbs = rcu_get_n_cbs_cpu(cpu);
 700                 if (!cbs)
 701                         continue;
 702                 if (max_cpu < 0)
 703                         pr_info("%s: callbacks", __func__);
 704                 pr_cont(" %d: %lu", cpu, cbs);
 705                 if (cbs <= max_cbs)
 706                         continue;
 707                 max_cbs = cbs;
 708                 max_cpu = cpu;
 709         }
 710         if (max_cpu >= 0)
 711                 pr_cont("\n");
 712 }
 713 EXPORT_SYMBOL_GPL(rcu_fwd_progress_check);
 714
 715 /* Commandeer a sysrq key to dump RCU's tree. */
 716 static bool sysrq_rcu;
 717 module_param(sysrq_rcu, bool, 0444);
 718
 719 /* Dump grace-period-request information due to commandeered sysrq. */
 720 static void sysrq_show_rcu(int key)
 721 {
 722         show_rcu_gp_kthreads();
 723 }
 724
 725 static struct sysrq_key_op sysrq_rcudump_op = {
 726         .handler = sysrq_show_rcu,
 727         .help_msg = "show-rcu(y)",
 728         .action_msg = "Show RCU tree",
 729         .enable_mask = SYSRQ_ENABLE_DUMP,
 730 };
 731
 732 static int __init rcu_sysrq_init(void)
 733 {
 734         if (sysrq_rcu)
 735                 return register_sysrq_key('y', &sysrq_rcudump_op);
 736         return 0;
 737 }
 738 early_initcall(rcu_sysrq_init);