LCOV - code coverage report
Current view: top level - kernel/rcu - tree_exp.h (source / functions) Hit Total Coverage
Test: combined.info Lines: 8 364 2.2 %
Date: 2022-03-28 13:20:08 Functions: 1 19 5.3 %
Branches: 1 194 0.5 %

           Branch data     Line data    Source code
       1                 :            : /* SPDX-License-Identifier: GPL-2.0+ */
       2                 :            : /*
       3                 :            :  * RCU expedited grace periods
       4                 :            :  *
       5                 :            :  * Copyright IBM Corporation, 2016
       6                 :            :  *
       7                 :            :  * Authors: Paul E. McKenney <paulmck@linux.ibm.com>
       8                 :            :  */
       9                 :            : 
      10                 :            : #include <linux/lockdep.h>
      11                 :            : 
      12                 :            : static void rcu_exp_handler(void *unused);
      13                 :            : static int rcu_print_task_exp_stall(struct rcu_node *rnp);
      14                 :            : 
      15                 :            : /*
      16                 :            :  * Record the start of an expedited grace period.
      17                 :            :  */
      18                 :          0 : static void rcu_exp_gp_seq_start(void)
      19                 :            : {
      20                 :          0 :         rcu_seq_start(&rcu_state.expedited_sequence);
      21                 :            : }
      22                 :            : 
      23                 :            : /*
      24                 :            :  * Return the value that the expedited-grace-period counter will have
      25                 :            :  * at the end of the current grace period.
      26                 :            :  */
      27                 :          0 : static __maybe_unused unsigned long rcu_exp_gp_seq_endval(void)
      28                 :            : {
      29                 :          0 :         return rcu_seq_endval(&rcu_state.expedited_sequence);
      30                 :            : }
      31                 :            : 
      32                 :            : /*
      33                 :            :  * Record the end of an expedited grace period.
      34                 :            :  */
      35                 :          0 : static void rcu_exp_gp_seq_end(void)
      36                 :            : {
      37                 :          0 :         rcu_seq_end(&rcu_state.expedited_sequence);
      38                 :          0 :         smp_mb(); /* Ensure that consecutive grace periods serialize. */
      39                 :          0 : }
      40                 :            : 
      41                 :            : /*
      42                 :            :  * Take a snapshot of the expedited-grace-period counter, which is the
      43                 :            :  * earliest value that will indicate that a full grace period has
      44                 :            :  * elapsed since the current time.
      45                 :            :  */
      46                 :          0 : static unsigned long rcu_exp_gp_seq_snap(void)
      47                 :            : {
      48                 :          0 :         unsigned long s;
      49                 :            : 
      50                 :          0 :         smp_mb(); /* Caller's modifications seen first by other CPUs. */
      51                 :          0 :         s = rcu_seq_snap(&rcu_state.expedited_sequence);
      52                 :          0 :         trace_rcu_exp_grace_period(rcu_state.name, s, TPS("snap"));
      53                 :          0 :         return s;
      54                 :            : }
      55                 :            : 
      56                 :            : /*
      57                 :            :  * Given a counter snapshot from rcu_exp_gp_seq_snap(), return true
      58                 :            :  * if a full expedited grace period has elapsed since that snapshot
      59                 :            :  * was taken.
      60                 :            :  */
      61                 :          0 : static bool rcu_exp_gp_seq_done(unsigned long s)
      62                 :            : {
      63                 :          0 :         return rcu_seq_done(&rcu_state.expedited_sequence, s);
      64                 :            : }
      65                 :            : 
      66                 :            : /*
      67                 :            :  * Reset the ->expmaskinit values in the rcu_node tree to reflect any
      68                 :            :  * recent CPU-online activity.  Note that these masks are not cleared
      69                 :            :  * when CPUs go offline, so they reflect the union of all CPUs that have
      70                 :            :  * ever been online.  This means that this function normally takes its
      71                 :            :  * no-work-to-do fastpath.
      72                 :            :  */
      73                 :          0 : static void sync_exp_reset_tree_hotplug(void)
      74                 :            : {
      75                 :          0 :         bool done;
      76                 :          0 :         unsigned long flags;
      77                 :          0 :         unsigned long mask;
      78                 :          0 :         unsigned long oldmask;
      79                 :          0 :         int ncpus = smp_load_acquire(&rcu_state.ncpus); /* Order vs. locking. */
      80                 :          0 :         struct rcu_node *rnp;
      81                 :          0 :         struct rcu_node *rnp_up;
      82                 :            : 
      83                 :            :         /* If no new CPUs onlined since last time, nothing to do. */
      84         [ #  # ]:          0 :         if (likely(ncpus == rcu_state.ncpus_snap))
      85                 :            :                 return;
      86                 :          0 :         rcu_state.ncpus_snap = ncpus;
      87                 :            : 
      88                 :            :         /*
      89                 :            :          * Each pass through the following loop propagates newly onlined
      90                 :            :          * CPUs for the current rcu_node structure up the rcu_node tree.
      91                 :            :          */
      92         [ #  # ]:          0 :         rcu_for_each_leaf_node(rnp) {
      93                 :          0 :                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
      94         [ #  # ]:          0 :                 if (rnp->expmaskinit == rnp->expmaskinitnext) {
      95                 :          0 :                         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
      96                 :          0 :                         continue;  /* No new CPUs, nothing to do. */
      97                 :            :                 }
      98                 :            : 
      99                 :            :                 /* Update this node's mask, track old value for propagation. */
     100                 :          0 :                 oldmask = rnp->expmaskinit;
     101                 :          0 :                 rnp->expmaskinit = rnp->expmaskinitnext;
     102                 :          0 :                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     103                 :            : 
     104                 :            :                 /* If was already nonzero, nothing to propagate. */
     105         [ #  # ]:          0 :                 if (oldmask)
     106                 :          0 :                         continue;
     107                 :            : 
     108                 :            :                 /* Propagate the new CPU up the tree. */
     109                 :          0 :                 mask = rnp->grpmask;
     110                 :          0 :                 rnp_up = rnp->parent;
     111                 :          0 :                 done = false;
     112         [ #  # ]:          0 :                 while (rnp_up) {
     113                 :          0 :                         raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
     114         [ #  # ]:          0 :                         if (rnp_up->expmaskinit)
     115                 :          0 :                                 done = true;
     116                 :          0 :                         rnp_up->expmaskinit |= mask;
     117                 :          0 :                         raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
     118         [ #  # ]:          0 :                         if (done)
     119                 :            :                                 break;
     120                 :          0 :                         mask = rnp_up->grpmask;
     121                 :          0 :                         rnp_up = rnp_up->parent;
     122                 :            :                 }
     123                 :            :         }
     124                 :            : }
     125                 :            : 
     126                 :            : /*
     127                 :            :  * Reset the ->expmask values in the rcu_node tree in preparation for
     128                 :            :  * a new expedited grace period.
     129                 :            :  */
     130                 :          0 : static void __maybe_unused sync_exp_reset_tree(void)
     131                 :            : {
     132                 :          0 :         unsigned long flags;
     133                 :          0 :         struct rcu_node *rnp;
     134                 :            : 
     135                 :          0 :         sync_exp_reset_tree_hotplug();
     136         [ #  # ]:          0 :         rcu_for_each_node_breadth_first(rnp) {
     137                 :          0 :                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
     138         [ #  # ]:          0 :                 WARN_ON_ONCE(rnp->expmask);
     139                 :          0 :                 WRITE_ONCE(rnp->expmask, rnp->expmaskinit);
     140                 :          0 :                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     141                 :            :         }
     142                 :          0 : }
     143                 :            : 
     144                 :            : /*
     145                 :            :  * Return non-zero if there is no RCU expedited grace period in progress
     146                 :            :  * for the specified rcu_node structure, in other words, if all CPUs and
     147                 :            :  * tasks covered by the specified rcu_node structure have done their bit
     148                 :            :  * for the current expedited grace period.
     149                 :            :  */
     150                 :          0 : static bool sync_rcu_exp_done(struct rcu_node *rnp)
     151                 :            : {
     152                 :          0 :         raw_lockdep_assert_held_rcu_node(rnp);
     153   [ #  #  #  # ]:          0 :         return rnp->exp_tasks == NULL &&
     154   [ #  #  #  # ]:          0 :                READ_ONCE(rnp->expmask) == 0;
     155                 :            : }
     156                 :            : 
     157                 :            : /*
     158                 :            :  * Like sync_rcu_exp_done(), but where the caller does not hold the
     159                 :            :  * rcu_node's ->lock.
     160                 :            :  */
     161                 :          0 : static bool sync_rcu_exp_done_unlocked(struct rcu_node *rnp)
     162                 :            : {
     163                 :          0 :         unsigned long flags;
     164                 :          0 :         bool ret;
     165                 :            : 
     166                 :          0 :         raw_spin_lock_irqsave_rcu_node(rnp, flags);
     167         [ #  # ]:          0 :         ret = sync_rcu_exp_done(rnp);
     168                 :          0 :         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     169                 :            : 
     170                 :          0 :         return ret;
     171                 :            : }
     172                 :            : 
     173                 :            : 
     174                 :            : /*
     175                 :            :  * Report the exit from RCU read-side critical section for the last task
     176                 :            :  * that queued itself during or before the current expedited preemptible-RCU
     177                 :            :  * grace period.  This event is reported either to the rcu_node structure on
     178                 :            :  * which the task was queued or to one of that rcu_node structure's ancestors,
     179                 :            :  * recursively up the tree.  (Calm down, calm down, we do the recursion
     180                 :            :  * iteratively!)
     181                 :            :  */
     182                 :          0 : static void __rcu_report_exp_rnp(struct rcu_node *rnp,
     183                 :            :                                  bool wake, unsigned long flags)
     184                 :            :         __releases(rnp->lock)
     185                 :            : {
     186                 :          0 :         unsigned long mask;
     187                 :            : 
     188                 :          0 :         raw_lockdep_assert_held_rcu_node(rnp);
     189                 :          0 :         for (;;) {
     190   [ #  #  #  # ]:          0 :                 if (!sync_rcu_exp_done(rnp)) {
     191         [ #  # ]:          0 :                         if (!rnp->expmask)
     192                 :          0 :                                 rcu_initiate_boost(rnp, flags);
     193                 :            :                         else
     194                 :          0 :                                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     195                 :            :                         break;
     196                 :            :                 }
     197         [ #  # ]:          0 :                 if (rnp->parent == NULL) {
     198                 :          0 :                         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     199         [ #  # ]:          0 :                         if (wake) {
     200                 :          0 :                                 smp_mb(); /* EGP done before wake_up(). */
     201                 :          0 :                                 swake_up_one(&rcu_state.expedited_wq);
     202                 :            :                         }
     203                 :            :                         break;
     204                 :            :                 }
     205                 :          0 :                 mask = rnp->grpmask;
     206                 :          0 :                 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
     207                 :          0 :                 rnp = rnp->parent;
     208                 :          0 :                 raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
     209         [ #  # ]:          0 :                 WARN_ON_ONCE(!(rnp->expmask & mask));
     210                 :          0 :                 WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
     211                 :            :         }
     212                 :          0 : }
     213                 :            : 
     214                 :            : /*
     215                 :            :  * Report expedited quiescent state for specified node.  This is a
     216                 :            :  * lock-acquisition wrapper function for __rcu_report_exp_rnp().
     217                 :            :  */
     218                 :            : static void __maybe_unused rcu_report_exp_rnp(struct rcu_node *rnp, bool wake)
     219                 :            : {
     220                 :            :         unsigned long flags;
     221                 :            : 
     222                 :            :         raw_spin_lock_irqsave_rcu_node(rnp, flags);
     223                 :            :         __rcu_report_exp_rnp(rnp, wake, flags);
     224                 :            : }
     225                 :            : 
     226                 :            : /*
     227                 :            :  * Report expedited quiescent state for multiple CPUs, all covered by the
     228                 :            :  * specified leaf rcu_node structure.
     229                 :            :  */
     230                 :          0 : static void rcu_report_exp_cpu_mult(struct rcu_node *rnp,
     231                 :            :                                     unsigned long mask, bool wake)
     232                 :            : {
     233                 :          0 :         int cpu;
     234                 :          0 :         unsigned long flags;
     235                 :          0 :         struct rcu_data *rdp;
     236                 :            : 
     237                 :          0 :         raw_spin_lock_irqsave_rcu_node(rnp, flags);
     238         [ #  # ]:          0 :         if (!(rnp->expmask & mask)) {
     239                 :          0 :                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     240                 :          0 :                 return;
     241                 :            :         }
     242                 :          0 :         WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
     243         [ #  # ]:          0 :         for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
     244                 :          0 :                 rdp = per_cpu_ptr(&rcu_data, cpu);
     245                 :          0 :                 if (!IS_ENABLED(CONFIG_NO_HZ_FULL) || !rdp->rcu_forced_tick_exp)
     246                 :          0 :                         continue;
     247                 :            :                 rdp->rcu_forced_tick_exp = false;
     248                 :            :                 tick_dep_clear_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
     249                 :            :         }
     250                 :          0 :         __rcu_report_exp_rnp(rnp, wake, flags); /* Releases rnp->lock. */
     251                 :            : }
     252                 :            : 
     253                 :            : /*
     254                 :            :  * Report expedited quiescent state for specified rcu_data (CPU).
     255                 :            :  */
     256                 :          0 : static void rcu_report_exp_rdp(struct rcu_data *rdp)
     257                 :            : {
     258                 :          0 :         WRITE_ONCE(rdp->exp_deferred_qs, false);
     259                 :          0 :         rcu_report_exp_cpu_mult(rdp->mynode, rdp->grpmask, true);
     260                 :          0 : }
     261                 :            : 
     262                 :            : /* Common code for work-done checking. */
     263                 :          0 : static bool sync_exp_work_done(unsigned long s)
     264                 :            : {
     265         [ #  # ]:          0 :         if (rcu_exp_gp_seq_done(s)) {
     266                 :          0 :                 trace_rcu_exp_grace_period(rcu_state.name, s, TPS("done"));
     267                 :          0 :                 smp_mb(); /* Ensure test happens before caller kfree(). */
     268                 :          0 :                 return true;
     269                 :            :         }
     270                 :            :         return false;
     271                 :            : }
     272                 :            : 
     273                 :            : /*
     274                 :            :  * Funnel-lock acquisition for expedited grace periods.  Returns true
     275                 :            :  * if some other task completed an expedited grace period that this task
     276                 :            :  * can piggy-back on, and with no mutex held.  Otherwise, returns false
     277                 :            :  * with the mutex held, indicating that the caller must actually do the
     278                 :            :  * expedited grace period.
     279                 :            :  */
     280                 :          0 : static bool exp_funnel_lock(unsigned long s)
     281                 :            : {
     282                 :          0 :         struct rcu_data *rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
     283                 :          0 :         struct rcu_node *rnp = rdp->mynode;
     284         [ #  # ]:          0 :         struct rcu_node *rnp_root = rcu_get_root();
     285                 :            : 
     286                 :            :         /* Low-contention fastpath. */
     287   [ #  #  #  # ]:          0 :         if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&
     288         [ #  # ]:          0 :             (rnp == rnp_root ||
     289   [ #  #  #  # ]:          0 :              ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&
     290                 :          0 :             mutex_trylock(&rcu_state.exp_mutex))
     291                 :          0 :                 goto fastpath;
     292                 :            : 
     293                 :            :         /*
     294                 :            :          * Each pass through the following loop works its way up
     295                 :            :          * the rcu_node tree, returning if others have done the work or
     296                 :            :          * otherwise falls through to acquire ->exp_mutex.  The mapping
     297                 :            :          * from CPU to rcu_node structure can be inexact, as it is just
     298                 :            :          * promoting locality and is not strictly needed for correctness.
     299                 :            :          */
     300         [ #  # ]:          0 :         for (; rnp != NULL; rnp = rnp->parent) {
     301         [ #  # ]:          0 :                 if (sync_exp_work_done(s))
     302                 :            :                         return true;
     303                 :            : 
     304                 :            :                 /* Work not done, either wait here or go up. */
     305                 :          0 :                 spin_lock(&rnp->exp_lock);
     306         [ #  # ]:          0 :                 if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {
     307                 :            : 
     308                 :            :                         /* Someone else doing GP, so wait for them. */
     309                 :          0 :                         spin_unlock(&rnp->exp_lock);
     310                 :          0 :                         trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
     311                 :            :                                                   rnp->grplo, rnp->grphi,
     312                 :          0 :                                                   TPS("wait"));
     313   [ #  #  #  # ]:          0 :                         wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
     314                 :            :                                    sync_exp_work_done(s));
     315                 :          0 :                         return true;
     316                 :            :                 }
     317                 :          0 :                 rnp->exp_seq_rq = s; /* Followers can wait on us. */
     318                 :          0 :                 spin_unlock(&rnp->exp_lock);
     319                 :          0 :                 trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
     320                 :          0 :                                           rnp->grplo, rnp->grphi, TPS("nxtlvl"));
     321                 :            :         }
     322                 :          0 :         mutex_lock(&rcu_state.exp_mutex);
     323                 :          0 : fastpath:
     324         [ #  # ]:          0 :         if (sync_exp_work_done(s)) {
     325                 :          0 :                 mutex_unlock(&rcu_state.exp_mutex);
     326                 :          0 :                 return true;
     327                 :            :         }
     328                 :          0 :         rcu_exp_gp_seq_start();
     329                 :          0 :         trace_rcu_exp_grace_period(rcu_state.name, s, TPS("start"));
     330                 :          0 :         return false;
     331                 :            : }
     332                 :            : 
     333                 :            : /*
     334                 :            :  * Select the CPUs within the specified rcu_node that the upcoming
     335                 :            :  * expedited grace period needs to wait for.
     336                 :            :  */
     337                 :          0 : static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
     338                 :            : {
     339                 :          0 :         int cpu;
     340                 :          0 :         unsigned long flags;
     341                 :          0 :         unsigned long mask_ofl_test;
     342                 :          0 :         unsigned long mask_ofl_ipi;
     343                 :          0 :         int ret;
     344                 :          0 :         struct rcu_exp_work *rewp =
     345                 :          0 :                 container_of(wp, struct rcu_exp_work, rew_work);
     346                 :          0 :         struct rcu_node *rnp = container_of(rewp, struct rcu_node, rew);
     347                 :            : 
     348                 :          0 :         raw_spin_lock_irqsave_rcu_node(rnp, flags);
     349                 :            : 
     350                 :            :         /* Each pass checks a CPU for identity, offline, and idle. */
     351                 :          0 :         mask_ofl_test = 0;
     352         [ #  # ]:          0 :         for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) {
     353                 :          0 :                 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
     354                 :          0 :                 unsigned long mask = rdp->grpmask;
     355                 :          0 :                 int snap;
     356                 :            : 
     357         [ #  # ]:          0 :                 if (raw_smp_processor_id() == cpu ||
     358         [ #  # ]:          0 :                     !(rnp->qsmaskinitnext & mask)) {
     359                 :          0 :                         mask_ofl_test |= mask;
     360                 :            :                 } else {
     361                 :          0 :                         snap = rcu_dynticks_snap(rdp);
     362         [ #  # ]:          0 :                         if (rcu_dynticks_in_eqs(snap))
     363                 :          0 :                                 mask_ofl_test |= mask;
     364                 :            :                         else
     365                 :          0 :                                 rdp->exp_dynticks_snap = snap;
     366                 :            :                 }
     367                 :            :         }
     368                 :          0 :         mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
     369                 :            : 
     370                 :            :         /*
     371                 :            :          * Need to wait for any blocked tasks as well.  Note that
     372                 :            :          * additional blocking tasks will also block the expedited GP
     373                 :            :          * until such time as the ->expmask bits are cleared.
     374                 :            :          */
     375                 :          0 :         if (rcu_preempt_has_tasks(rnp))
     376                 :            :                 rnp->exp_tasks = rnp->blkd_tasks.next;
     377                 :          0 :         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     378                 :            : 
     379                 :            :         /* IPI the remaining CPUs for expedited quiescent state. */
     380         [ #  # ]:          0 :         for_each_leaf_node_cpu_mask(rnp, cpu, mask_ofl_ipi) {
     381                 :          0 :                 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
     382                 :          0 :                 unsigned long mask = rdp->grpmask;
     383                 :            : 
     384                 :          0 : retry_ipi:
     385         [ #  # ]:          0 :                 if (rcu_dynticks_in_eqs_since(rdp, rdp->exp_dynticks_snap)) {
     386                 :          0 :                         mask_ofl_test |= mask;
     387                 :          0 :                         continue;
     388                 :            :                 }
     389         [ #  # ]:          0 :                 if (get_cpu() == cpu) {
     390                 :          0 :                         put_cpu();
     391                 :          0 :                         continue;
     392                 :            :                 }
     393                 :          0 :                 ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
     394                 :          0 :                 put_cpu();
     395                 :            :                 /* The CPU will report the QS in response to the IPI. */
     396         [ #  # ]:          0 :                 if (!ret)
     397                 :          0 :                         continue;
     398                 :            : 
     399                 :            :                 /* Failed, raced with CPU hotplug operation. */
     400                 :          0 :                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
     401         [ #  # ]:          0 :                 if ((rnp->qsmaskinitnext & mask) &&
     402         [ #  # ]:          0 :                     (rnp->expmask & mask)) {
     403                 :            :                         /* Online, so delay for a bit and try again. */
     404                 :          0 :                         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     405                 :          0 :                         trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("selectofl"));
     406                 :          0 :                         schedule_timeout_uninterruptible(1);
     407                 :          0 :                         goto retry_ipi;
     408                 :            :                 }
     409                 :            :                 /* CPU really is offline, so we must report its QS. */
     410         [ #  # ]:          0 :                 if (rnp->expmask & mask)
     411                 :          0 :                         mask_ofl_test |= mask;
     412                 :          0 :                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     413                 :            :         }
     414                 :            :         /* Report quiescent states for those that went offline. */
     415         [ #  # ]:          0 :         if (mask_ofl_test)
     416                 :          0 :                 rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false);
     417                 :          0 : }
     418                 :            : 
     419                 :            : /*
     420                 :            :  * Select the nodes that the upcoming expedited grace period needs
     421                 :            :  * to wait for.
     422                 :            :  */
     423                 :          0 : static void sync_rcu_exp_select_cpus(void)
     424                 :            : {
     425                 :          0 :         int cpu;
     426                 :          0 :         struct rcu_node *rnp;
     427                 :            : 
     428                 :          0 :         trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("reset"));
     429                 :          0 :         sync_exp_reset_tree();
     430                 :          0 :         trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("select"));
     431                 :            : 
     432                 :            :         /* Schedule work for each leaf rcu_node structure. */
     433         [ #  # ]:          0 :         rcu_for_each_leaf_node(rnp) {
     434                 :          0 :                 rnp->exp_need_flush = false;
     435         [ #  # ]:          0 :                 if (!READ_ONCE(rnp->expmask))
     436                 :          0 :                         continue; /* Avoid early boot non-existent wq. */
     437         [ #  # ]:          0 :                 if (!READ_ONCE(rcu_par_gp_wq) ||
     438         [ #  # ]:          0 :                     rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
     439         [ #  # ]:          0 :                     rcu_is_last_leaf_node(rnp)) {
     440                 :            :                         /* No workqueues yet or last leaf, do direct call. */
     441                 :          0 :                         sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work);
     442                 :          0 :                         continue;
     443                 :            :                 }
     444                 :          0 :                 INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
     445                 :          0 :                 cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
     446                 :            :                 /* If all offline, queue the work on an unbound CPU. */
     447         [ #  # ]:          0 :                 if (unlikely(cpu > rnp->grphi - rnp->grplo))
     448                 :            :                         cpu = WORK_CPU_UNBOUND;
     449                 :            :                 else
     450                 :          0 :                         cpu += rnp->grplo;
     451                 :          0 :                 queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
     452                 :          0 :                 rnp->exp_need_flush = true;
     453                 :            :         }
     454                 :            : 
     455                 :            :         /* Wait for workqueue jobs (if any) to complete. */
     456         [ #  # ]:          0 :         rcu_for_each_leaf_node(rnp)
     457         [ #  # ]:          0 :                 if (rnp->exp_need_flush)
     458                 :          0 :                         flush_work(&rnp->rew.rew_work);
     459                 :          0 : }
     460                 :            : 
     461                 :            : /*
     462                 :            :  * Wait for the expedited grace period to elapse, within time limit.
     463                 :            :  * If the time limit is exceeded without the grace period elapsing,
     464                 :            :  * return false, otherwise return true.
     465                 :            :  */
     466                 :          0 : static bool synchronize_rcu_expedited_wait_once(long tlimit)
     467                 :            : {
     468                 :          0 :         int t;
     469                 :          0 :         struct rcu_node *rnp_root = rcu_get_root();
     470                 :            : 
     471   [ #  #  #  #  :          0 :         t = swait_event_timeout_exclusive(rcu_state.expedited_wq,
             #  #  #  # ]
     472                 :            :                                           sync_rcu_exp_done_unlocked(rnp_root),
     473                 :            :                                           tlimit);
     474                 :            :         // Workqueues should not be signaled.
     475   [ #  #  #  # ]:          0 :         if (t > 0 || sync_rcu_exp_done_unlocked(rnp_root))
     476                 :          0 :                 return true;
     477         [ #  # ]:          0 :         WARN_ON(t < 0);  /* workqueues should not be signaled. */
     478                 :            :         return false;
     479                 :            : }
     480                 :            : 
     481                 :            : /*
     482                 :            :  * Wait for the expedited grace period to elapse, issuing any needed
     483                 :            :  * RCU CPU stall warnings along the way.
     484                 :            :  */
     485                 :          0 : static void synchronize_rcu_expedited_wait(void)
     486                 :            : {
     487                 :          0 :         int cpu;
     488                 :          0 :         unsigned long jiffies_stall;
     489                 :          0 :         unsigned long jiffies_start;
     490                 :          0 :         unsigned long mask;
     491                 :          0 :         int ndetected;
     492                 :          0 :         struct rcu_data *rdp;
     493                 :          0 :         struct rcu_node *rnp;
     494                 :          0 :         struct rcu_node *rnp_root = rcu_get_root();
     495                 :            : 
     496                 :          0 :         trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait"));
     497         [ #  # ]:          0 :         jiffies_stall = rcu_jiffies_till_stall_check();
     498                 :          0 :         jiffies_start = jiffies;
     499                 :          0 :         if (IS_ENABLED(CONFIG_NO_HZ_FULL)) {
     500                 :            :                 if (synchronize_rcu_expedited_wait_once(1))
     501                 :            :                         return;
     502                 :            :                 rcu_for_each_leaf_node(rnp) {
     503                 :            :                         for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) {
     504                 :            :                                 rdp = per_cpu_ptr(&rcu_data, cpu);
     505                 :            :                                 if (rdp->rcu_forced_tick_exp)
     506                 :            :                                         continue;
     507                 :            :                                 rdp->rcu_forced_tick_exp = true;
     508                 :            :                                 tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
     509                 :            :                         }
     510                 :            :                 }
     511                 :            :         }
     512                 :            : 
     513                 :          0 :         for (;;) {
     514         [ #  # ]:          0 :                 if (synchronize_rcu_expedited_wait_once(jiffies_stall))
     515                 :          0 :                         return;
     516         [ #  # ]:          0 :                 if (rcu_cpu_stall_suppress)
     517                 :          0 :                         continue;
     518         [ #  # ]:          0 :                 panic_on_rcu_stall();
     519                 :          0 :                 pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
     520                 :            :                        rcu_state.name);
     521                 :          0 :                 ndetected = 0;
     522         [ #  # ]:          0 :                 rcu_for_each_leaf_node(rnp) {
     523                 :          0 :                         ndetected += rcu_print_task_exp_stall(rnp);
     524         [ #  # ]:          0 :                         for_each_leaf_node_possible_cpu(rnp, cpu) {
     525                 :          0 :                                 struct rcu_data *rdp;
     526                 :            : 
     527                 :          0 :                                 mask = leaf_node_cpu_bit(rnp, cpu);
     528         [ #  # ]:          0 :                                 if (!(READ_ONCE(rnp->expmask) & mask))
     529                 :          0 :                                         continue;
     530                 :          0 :                                 ndetected++;
     531                 :          0 :                                 rdp = per_cpu_ptr(&rcu_data, cpu);
     532                 :          0 :                                 pr_cont(" %d-%c%c%c", cpu,
     533                 :            :                                         "O."[!!cpu_online(cpu)],
     534                 :            :                                         "o."[!!(rdp->grpmask & rnp->expmaskinit)],
     535                 :            :                                         "N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
     536                 :            :                         }
     537                 :            :                 }
     538                 :          0 :                 pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
     539                 :            :                         jiffies - jiffies_start, rcu_state.expedited_sequence,
     540                 :            :                         READ_ONCE(rnp_root->expmask),
     541                 :            :                         ".T"[!!rnp_root->exp_tasks]);
     542         [ #  # ]:          0 :                 if (ndetected) {
     543                 :          0 :                         pr_err("blocking rcu_node structures:");
     544         [ #  # ]:          0 :                         rcu_for_each_node_breadth_first(rnp) {
     545         [ #  # ]:          0 :                                 if (rnp == rnp_root)
     546                 :          0 :                                         continue; /* printed unconditionally */
     547         [ #  # ]:          0 :                                 if (sync_rcu_exp_done_unlocked(rnp))
     548                 :          0 :                                         continue;
     549                 :          0 :                                 pr_cont(" l=%u:%d-%d:%#lx/%c",
     550                 :            :                                         rnp->level, rnp->grplo, rnp->grphi,
     551                 :            :                                         READ_ONCE(rnp->expmask),
     552                 :            :                                         ".T"[!!rnp->exp_tasks]);
     553                 :            :                         }
     554                 :          0 :                         pr_cont("\n");
     555                 :            :                 }
     556         [ #  # ]:          0 :                 rcu_for_each_leaf_node(rnp) {
     557         [ #  # ]:          0 :                         for_each_leaf_node_possible_cpu(rnp, cpu) {
     558                 :          0 :                                 mask = leaf_node_cpu_bit(rnp, cpu);
     559         [ #  # ]:          0 :                                 if (!(READ_ONCE(rnp->expmask) & mask))
     560                 :          0 :                                         continue;
     561                 :          0 :                                 dump_cpu_task(cpu);
     562                 :            :                         }
     563                 :            :                 }
     564         [ #  # ]:          0 :                 jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;
     565                 :            :         }
     566                 :            : }
     567                 :            : 
     568                 :            : /*
     569                 :            :  * Wait for the current expedited grace period to complete, and then
     570                 :            :  * wake up everyone who piggybacked on the just-completed expedited
     571                 :            :  * grace period.  Also update all the ->exp_seq_rq counters as needed
     572                 :            :  * in order to avoid counter-wrap problems.
     573                 :            :  */
     574                 :          0 : static void rcu_exp_wait_wake(unsigned long s)
     575                 :            : {
     576                 :          0 :         struct rcu_node *rnp;
     577                 :            : 
     578                 :          0 :         synchronize_rcu_expedited_wait();
     579                 :            : 
     580                 :            :         // Switch over to wakeup mode, allowing the next GP to proceed.
     581                 :            :         // End the previous grace period only after acquiring the mutex
     582                 :            :         // to ensure that only one GP runs concurrently with wakeups.
     583                 :          0 :         mutex_lock(&rcu_state.exp_wake_mutex);
     584                 :          0 :         rcu_exp_gp_seq_end();
     585                 :          0 :         trace_rcu_exp_grace_period(rcu_state.name, s, TPS("end"));
     586                 :            : 
     587         [ #  # ]:          0 :         rcu_for_each_node_breadth_first(rnp) {
     588         [ #  # ]:          0 :                 if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {
     589                 :          0 :                         spin_lock(&rnp->exp_lock);
     590                 :            :                         /* Recheck, avoid hang in case someone just arrived. */
     591         [ #  # ]:          0 :                         if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
     592                 :          0 :                                 rnp->exp_seq_rq = s;
     593                 :          0 :                         spin_unlock(&rnp->exp_lock);
     594                 :            :                 }
     595                 :          0 :                 smp_mb(); /* All above changes before wakeup. */
     596                 :          0 :                 wake_up_all(&rnp->exp_wq[rcu_seq_ctr(s) & 0x3]);
     597                 :            :         }
     598                 :          0 :         trace_rcu_exp_grace_period(rcu_state.name, s, TPS("endwake"));
     599                 :          0 :         mutex_unlock(&rcu_state.exp_wake_mutex);
     600                 :          0 : }
     601                 :            : 
     602                 :            : /*
     603                 :            :  * Common code to drive an expedited grace period forward, used by
     604                 :            :  * workqueues and mid-boot-time tasks.
     605                 :            :  */
     606                 :          0 : static void rcu_exp_sel_wait_wake(unsigned long s)
     607                 :            : {
     608                 :            :         /* Initialize the rcu_node tree in preparation for the wait. */
     609                 :          0 :         sync_rcu_exp_select_cpus();
     610                 :            : 
     611                 :            :         /* Wait and clean up, including waking everyone. */
     612                 :          0 :         rcu_exp_wait_wake(s);
     613                 :          0 : }
     614                 :            : 
     615                 :            : /*
     616                 :            :  * Work-queue handler to drive an expedited grace period forward.
     617                 :            :  */
     618                 :          0 : static void wait_rcu_exp_gp(struct work_struct *wp)
     619                 :            : {
     620                 :          0 :         struct rcu_exp_work *rewp;
     621                 :            : 
     622                 :          0 :         rewp = container_of(wp, struct rcu_exp_work, rew_work);
     623                 :          0 :         rcu_exp_sel_wait_wake(rewp->rew_s);
     624                 :          0 : }
     625                 :            : 
     626                 :            : #ifdef CONFIG_PREEMPT_RCU
     627                 :            : 
     628                 :            : /*
     629                 :            :  * Remote handler for smp_call_function_single().  If there is an
     630                 :            :  * RCU read-side critical section in effect, request that the
     631                 :            :  * next rcu_read_unlock() record the quiescent state up the
     632                 :            :  * ->expmask fields in the rcu_node tree.  Otherwise, immediately
     633                 :            :  * report the quiescent state.
     634                 :            :  */
     635                 :            : static void rcu_exp_handler(void *unused)
     636                 :            : {
     637                 :            :         unsigned long flags;
     638                 :            :         struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
     639                 :            :         struct rcu_node *rnp = rdp->mynode;
     640                 :            :         struct task_struct *t = current;
     641                 :            : 
     642                 :            :         /*
     643                 :            :          * First, the common case of not being in an RCU read-side
     644                 :            :          * critical section.  If also enabled or idle, immediately
     645                 :            :          * report the quiescent state, otherwise defer.
     646                 :            :          */
     647                 :            :         if (!rcu_preempt_depth()) {
     648                 :            :                 if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) ||
     649                 :            :                     rcu_dynticks_curr_cpu_in_eqs()) {
     650                 :            :                         rcu_report_exp_rdp(rdp);
     651                 :            :                 } else {
     652                 :            :                         rdp->exp_deferred_qs = true;
     653                 :            :                         set_tsk_need_resched(t);
     654                 :            :                         set_preempt_need_resched();
     655                 :            :                 }
     656                 :            :                 return;
     657                 :            :         }
     658                 :            : 
     659                 :            :         /*
     660                 :            :          * Second, the less-common case of being in an RCU read-side
     661                 :            :          * critical section.  In this case we can count on a future
     662                 :            :          * rcu_read_unlock().  However, this rcu_read_unlock() might
     663                 :            :          * execute on some other CPU, but in that case there will be
     664                 :            :          * a future context switch.  Either way, if the expedited
     665                 :            :          * grace period is still waiting on this CPU, set ->deferred_qs
     666                 :            :          * so that the eventual quiescent state will be reported.
     667                 :            :          * Note that there is a large group of race conditions that
     668                 :            :          * can have caused this quiescent state to already have been
     669                 :            :          * reported, so we really do need to check ->expmask.
     670                 :            :          */
     671                 :            :         if (rcu_preempt_depth() > 0) {
     672                 :            :                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
     673                 :            :                 if (rnp->expmask & rdp->grpmask) {
     674                 :            :                         rdp->exp_deferred_qs = true;
     675                 :            :                         t->rcu_read_unlock_special.b.exp_hint = true;
     676                 :            :                 }
     677                 :            :                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
     678                 :            :                 return;
     679                 :            :         }
     680                 :            : 
     681                 :            :         /*
     682                 :            :          * The final and least likely case is where the interrupted
     683                 :            :          * code was just about to or just finished exiting the RCU-preempt
     684                 :            :          * read-side critical section, and no, we can't tell which.
     685                 :            :          * So either way, set ->deferred_qs to flag later code that
     686                 :            :          * a quiescent state is required.
     687                 :            :          *
     688                 :            :          * If the CPU is fully enabled (or if some buggy RCU-preempt
     689                 :            :          * read-side critical section is being used from idle), just
     690                 :            :          * invoke rcu_preempt_deferred_qs() to immediately report the
     691                 :            :          * quiescent state.  We cannot use rcu_read_unlock_special()
     692                 :            :          * because we are in an interrupt handler, which will cause that
     693                 :            :          * function to take an early exit without doing anything.
     694                 :            :          *
     695                 :            :          * Otherwise, force a context switch after the CPU enables everything.
     696                 :            :          */
     697                 :            :         rdp->exp_deferred_qs = true;
     698                 :            :         if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) ||
     699                 :            :             WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs())) {
     700                 :            :                 rcu_preempt_deferred_qs(t);
     701                 :            :         } else {
     702                 :            :                 set_tsk_need_resched(t);
     703                 :            :                 set_preempt_need_resched();
     704                 :            :         }
     705                 :            : }
     706                 :            : 
     707                 :            : /* PREEMPTION=y, so no PREEMPTION=n expedited grace period to clean up after. */
     708                 :            : static void sync_sched_exp_online_cleanup(int cpu)
     709                 :            : {
     710                 :            : }
     711                 :            : 
     712                 :            : /*
     713                 :            :  * Scan the current list of tasks blocked within RCU read-side critical
     714                 :            :  * sections, printing out the tid of each that is blocking the current
     715                 :            :  * expedited grace period.
     716                 :            :  */
     717                 :            : static int rcu_print_task_exp_stall(struct rcu_node *rnp)
     718                 :            : {
     719                 :            :         struct task_struct *t;
     720                 :            :         int ndetected = 0;
     721                 :            : 
     722                 :            :         if (!rnp->exp_tasks)
     723                 :            :                 return 0;
     724                 :            :         t = list_entry(rnp->exp_tasks->prev,
     725                 :            :                        struct task_struct, rcu_node_entry);
     726                 :            :         list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
     727                 :            :                 pr_cont(" P%d", t->pid);
     728                 :            :                 ndetected++;
     729                 :            :         }
     730                 :            :         return ndetected;
     731                 :            : }
     732                 :            : 
     733                 :            : #else /* #ifdef CONFIG_PREEMPT_RCU */
     734                 :            : 
     735                 :            : /* Request an expedited quiescent state. */
     736                 :          0 : static void rcu_exp_need_qs(void)
     737                 :            : {
     738                 :          0 :         __this_cpu_write(rcu_data.cpu_no_qs.b.exp, true);
     739                 :            :         /* Store .exp before .rcu_urgent_qs. */
     740                 :          0 :         smp_store_release(this_cpu_ptr(&rcu_data.rcu_urgent_qs), true);
     741                 :          0 :         set_tsk_need_resched(current);
     742                 :          0 :         set_preempt_need_resched();
     743                 :          0 : }
     744                 :            : 
     745                 :            : /* Invoked on each online non-idle CPU for expedited quiescent state. */
     746                 :          0 : static void rcu_exp_handler(void *unused)
     747                 :            : {
     748                 :          0 :         struct rcu_data *rdp;
     749                 :          0 :         struct rcu_node *rnp;
     750                 :            : 
     751                 :          0 :         rdp = this_cpu_ptr(&rcu_data);
     752                 :          0 :         rnp = rdp->mynode;
     753   [ #  #  #  # ]:          0 :         if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
     754         [ #  # ]:          0 :             __this_cpu_read(rcu_data.cpu_no_qs.b.exp))
     755                 :            :                 return;
     756   [ #  #  #  # ]:          0 :         if (rcu_is_cpu_rrupt_from_idle()) {
     757                 :          0 :                 rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
     758                 :          0 :                 return;
     759                 :            :         }
     760                 :          0 :         rcu_exp_need_qs();
     761                 :            : }
     762                 :            : 
     763                 :            : /* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
     764                 :          0 : static void sync_sched_exp_online_cleanup(int cpu)
     765                 :            : {
     766                 :          0 :         unsigned long flags;
     767                 :          0 :         int my_cpu;
     768                 :          0 :         struct rcu_data *rdp;
     769                 :          0 :         int ret;
     770                 :          0 :         struct rcu_node *rnp;
     771                 :            : 
     772                 :          0 :         rdp = per_cpu_ptr(&rcu_data, cpu);
     773                 :          0 :         rnp = rdp->mynode;
     774         [ #  # ]:          0 :         my_cpu = get_cpu();
     775                 :            :         /* Quiescent state either not needed or already requested, leave. */
     776   [ #  #  #  # ]:          0 :         if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
     777         [ #  # ]:          0 :             __this_cpu_read(rcu_data.cpu_no_qs.b.exp)) {
     778                 :          0 :                 put_cpu();
     779                 :          0 :                 return;
     780                 :            :         }
     781                 :            :         /* Quiescent state needed on current CPU, so set it up locally. */
     782         [ #  # ]:          0 :         if (my_cpu == cpu) {
     783                 :          0 :                 local_irq_save(flags);
     784                 :          0 :                 rcu_exp_need_qs();
     785                 :          0 :                 local_irq_restore(flags);
     786                 :          0 :                 put_cpu();
     787                 :          0 :                 return;
     788                 :            :         }
     789                 :            :         /* Quiescent state needed on some other CPU, send IPI. */
     790                 :          0 :         ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
     791                 :          0 :         put_cpu();
     792         [ #  # ]:          0 :         WARN_ON_ONCE(ret);
     793                 :            : }
     794                 :            : 
     795                 :            : /*
     796                 :            :  * Because preemptible RCU does not exist, we never have to check for
     797                 :            :  * tasks blocked within RCU read-side critical sections that are
     798                 :            :  * blocking the current expedited grace period.
     799                 :            :  */
     800                 :          0 : static int rcu_print_task_exp_stall(struct rcu_node *rnp)
     801                 :            : {
     802                 :          0 :         return 0;
     803                 :            : }
     804                 :            : 
     805                 :            : #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
     806                 :            : 
     807                 :            : /**
     808                 :            :  * synchronize_rcu_expedited - Brute-force RCU grace period
     809                 :            :  *
     810                 :            :  * Wait for an RCU grace period, but expedite it.  The basic idea is to
     811                 :            :  * IPI all non-idle non-nohz online CPUs.  The IPI handler checks whether
     812                 :            :  * the CPU is in an RCU critical section, and if so, it sets a flag that
     813                 :            :  * causes the outermost rcu_read_unlock() to report the quiescent state
     814                 :            :  * for RCU-preempt or asks the scheduler for help for RCU-sched.  On the
     815                 :            :  * other hand, if the CPU is not in an RCU read-side critical section,
     816                 :            :  * the IPI handler reports the quiescent state immediately.
     817                 :            :  *
     818                 :            :  * Although this is a great improvement over previous expedited
     819                 :            :  * implementations, it is still unfriendly to real-time workloads, so is
     820                 :            :  * thus not recommended for any sort of common-case code.  In fact, if
     821                 :            :  * you are using synchronize_rcu_expedited() in a loop, please restructure
     822                 :            :  * your code to batch your updates, and then use a single synchronize_rcu()
     823                 :            :  * instead.
     824                 :            :  *
     825                 :            :  * This has the same semantics as (but is more brutal than) synchronize_rcu().
     826                 :            :  */
     827                 :        155 : void synchronize_rcu_expedited(void)
     828                 :            : {
     829                 :        155 :         bool boottime = (rcu_scheduler_active == RCU_SCHEDULER_INIT);
     830                 :        155 :         struct rcu_exp_work rew;
     831                 :        155 :         struct rcu_node *rnp;
     832                 :        155 :         unsigned long s;
     833                 :            : 
     834                 :        155 :         RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
     835                 :            :                          lock_is_held(&rcu_lock_map) ||
     836                 :            :                          lock_is_held(&rcu_sched_lock_map),
     837                 :            :                          "Illegal synchronize_rcu_expedited() in RCU read-side critical section");
     838                 :            : 
     839                 :            :         /* Is the state is such that the call is a grace period? */
     840         [ -  + ]:        155 :         if (rcu_blocking_is_gp())
     841                 :        155 :                 return;
     842                 :            : 
     843                 :            :         /* If expedited grace periods are prohibited, fall back to normal. */
     844         [ #  # ]:          0 :         if (rcu_gp_is_normal()) {
     845                 :          0 :                 wait_rcu_gp(call_rcu);
     846                 :          0 :                 return;
     847                 :            :         }
     848                 :            : 
     849                 :            :         /* Take a snapshot of the sequence number.  */
     850                 :          0 :         s = rcu_exp_gp_seq_snap();
     851         [ #  # ]:          0 :         if (exp_funnel_lock(s))
     852                 :            :                 return;  /* Someone else did our work for us. */
     853                 :            : 
     854                 :            :         /* Ensure that load happens before action based on it. */
     855         [ #  # ]:          0 :         if (unlikely(boottime)) {
     856                 :            :                 /* Direct call during scheduler init and early_initcalls(). */
     857                 :          0 :                 rcu_exp_sel_wait_wake(s);
     858                 :            :         } else {
     859                 :            :                 /* Marshall arguments & schedule the expedited grace period. */
     860                 :          0 :                 rew.rew_s = s;
     861                 :          0 :                 INIT_WORK_ONSTACK(&rew.rew_work, wait_rcu_exp_gp);
     862                 :          0 :                 queue_work(rcu_gp_wq, &rew.rew_work);
     863                 :            :         }
     864                 :            : 
     865                 :            :         /* Wait for expedited grace period to complete. */
     866                 :          0 :         rnp = rcu_get_root();
     867   [ #  #  #  # ]:          0 :         wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
     868                 :            :                    sync_exp_work_done(s));
     869                 :          0 :         smp_mb(); /* Workqueue actions happen before return. */
     870                 :            : 
     871                 :            :         /* Let the next expedited grace period start. */
     872                 :          0 :         mutex_unlock(&rcu_state.exp_mutex);
     873                 :            : 
     874                 :          0 :         if (likely(!boottime))
     875                 :            :                 destroy_work_on_stack(&rew.rew_work);
     876                 :            : }
     877                 :            : EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

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