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867 lines
25 KiB
867 lines
25 KiB
/* SPDX-License-Identifier: GPL-2.0+ */ |
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/* |
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* RCU expedited grace periods |
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* |
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* Copyright IBM Corporation, 2016 |
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* |
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* Authors: Paul E. McKenney <[email protected]> |
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*/ |
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#include <linux/lockdep.h> |
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static void rcu_exp_handler(void *unused); |
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static int rcu_print_task_exp_stall(struct rcu_node *rnp); |
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|
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/* |
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* Record the start of an expedited grace period. |
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*/ |
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static void rcu_exp_gp_seq_start(void) |
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{ |
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rcu_seq_start(&rcu_state.expedited_sequence); |
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} |
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/* |
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* Return the value that the expedited-grace-period counter will have |
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* at the end of the current grace period. |
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*/ |
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static __maybe_unused unsigned long rcu_exp_gp_seq_endval(void) |
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{ |
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return rcu_seq_endval(&rcu_state.expedited_sequence); |
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} |
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/* |
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* Record the end of an expedited grace period. |
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*/ |
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static void rcu_exp_gp_seq_end(void) |
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{ |
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rcu_seq_end(&rcu_state.expedited_sequence); |
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smp_mb(); /* Ensure that consecutive grace periods serialize. */ |
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} |
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/* |
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* Take a snapshot of the expedited-grace-period counter, which is the |
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* earliest value that will indicate that a full grace period has |
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* elapsed since the current time. |
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*/ |
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static unsigned long rcu_exp_gp_seq_snap(void) |
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{ |
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unsigned long s; |
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smp_mb(); /* Caller's modifications seen first by other CPUs. */ |
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s = rcu_seq_snap(&rcu_state.expedited_sequence); |
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trace_rcu_exp_grace_period(rcu_state.name, s, TPS("snap")); |
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return s; |
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} |
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/* |
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* Given a counter snapshot from rcu_exp_gp_seq_snap(), return true |
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* if a full expedited grace period has elapsed since that snapshot |
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* was taken. |
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*/ |
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static bool rcu_exp_gp_seq_done(unsigned long s) |
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{ |
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return rcu_seq_done(&rcu_state.expedited_sequence, s); |
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} |
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/* |
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* Reset the ->expmaskinit values in the rcu_node tree to reflect any |
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* recent CPU-online activity. Note that these masks are not cleared |
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* when CPUs go offline, so they reflect the union of all CPUs that have |
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* ever been online. This means that this function normally takes its |
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* no-work-to-do fastpath. |
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*/ |
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static void sync_exp_reset_tree_hotplug(void) |
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{ |
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bool done; |
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unsigned long flags; |
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unsigned long mask; |
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unsigned long oldmask; |
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int ncpus = smp_load_acquire(&rcu_state.ncpus); /* Order vs. locking. */ |
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struct rcu_node *rnp; |
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struct rcu_node *rnp_up; |
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/* If no new CPUs onlined since last time, nothing to do. */ |
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if (likely(ncpus == rcu_state.ncpus_snap)) |
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return; |
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rcu_state.ncpus_snap = ncpus; |
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/* |
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* Each pass through the following loop propagates newly onlined |
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* CPUs for the current rcu_node structure up the rcu_node tree. |
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*/ |
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rcu_for_each_leaf_node(rnp) { |
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raw_spin_lock_irqsave_rcu_node(rnp, flags); |
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if (rnp->expmaskinit == rnp->expmaskinitnext) { |
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
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continue; /* No new CPUs, nothing to do. */ |
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} |
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/* Update this node's mask, track old value for propagation. */ |
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oldmask = rnp->expmaskinit; |
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rnp->expmaskinit = rnp->expmaskinitnext; |
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
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/* If was already nonzero, nothing to propagate. */ |
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if (oldmask) |
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continue; |
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/* Propagate the new CPU up the tree. */ |
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mask = rnp->grpmask; |
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rnp_up = rnp->parent; |
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done = false; |
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while (rnp_up) { |
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raw_spin_lock_irqsave_rcu_node(rnp_up, flags); |
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if (rnp_up->expmaskinit) |
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done = true; |
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rnp_up->expmaskinit |= mask; |
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raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags); |
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if (done) |
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break; |
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mask = rnp_up->grpmask; |
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rnp_up = rnp_up->parent; |
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} |
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} |
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} |
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/* |
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* Reset the ->expmask values in the rcu_node tree in preparation for |
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* a new expedited grace period. |
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*/ |
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static void __maybe_unused sync_exp_reset_tree(void) |
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{ |
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unsigned long flags; |
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struct rcu_node *rnp; |
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sync_exp_reset_tree_hotplug(); |
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rcu_for_each_node_breadth_first(rnp) { |
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raw_spin_lock_irqsave_rcu_node(rnp, flags); |
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WARN_ON_ONCE(rnp->expmask); |
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WRITE_ONCE(rnp->expmask, rnp->expmaskinit); |
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
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} |
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} |
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/* |
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* Return non-zero if there is no RCU expedited grace period in progress |
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* for the specified rcu_node structure, in other words, if all CPUs and |
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* tasks covered by the specified rcu_node structure have done their bit |
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* for the current expedited grace period. |
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*/ |
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static bool sync_rcu_exp_done(struct rcu_node *rnp) |
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{ |
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raw_lockdep_assert_held_rcu_node(rnp); |
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return READ_ONCE(rnp->exp_tasks) == NULL && |
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READ_ONCE(rnp->expmask) == 0; |
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} |
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/* |
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* Like sync_rcu_exp_done(), but where the caller does not hold the |
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* rcu_node's ->lock. |
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*/ |
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static bool sync_rcu_exp_done_unlocked(struct rcu_node *rnp) |
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{ |
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unsigned long flags; |
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bool ret; |
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raw_spin_lock_irqsave_rcu_node(rnp, flags); |
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ret = sync_rcu_exp_done(rnp); |
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
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return ret; |
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} |
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/* |
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* Report the exit from RCU read-side critical section for the last task |
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* that queued itself during or before the current expedited preemptible-RCU |
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* grace period. This event is reported either to the rcu_node structure on |
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* which the task was queued or to one of that rcu_node structure's ancestors, |
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* recursively up the tree. (Calm down, calm down, we do the recursion |
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* iteratively!) |
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*/ |
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static void __rcu_report_exp_rnp(struct rcu_node *rnp, |
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bool wake, unsigned long flags) |
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__releases(rnp->lock) |
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{ |
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unsigned long mask; |
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raw_lockdep_assert_held_rcu_node(rnp); |
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for (;;) { |
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if (!sync_rcu_exp_done(rnp)) { |
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if (!rnp->expmask) |
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rcu_initiate_boost(rnp, flags); |
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else |
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
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break; |
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} |
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if (rnp->parent == NULL) { |
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
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if (wake) { |
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smp_mb(); /* EGP done before wake_up(). */ |
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swake_up_one(&rcu_state.expedited_wq); |
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} |
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break; |
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} |
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mask = rnp->grpmask; |
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raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */ |
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rnp = rnp->parent; |
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raw_spin_lock_rcu_node(rnp); /* irqs already disabled */ |
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WARN_ON_ONCE(!(rnp->expmask & mask)); |
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WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask); |
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} |
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} |
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/* |
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* Report expedited quiescent state for specified node. This is a |
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* lock-acquisition wrapper function for __rcu_report_exp_rnp(). |
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*/ |
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static void __maybe_unused rcu_report_exp_rnp(struct rcu_node *rnp, bool wake) |
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{ |
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unsigned long flags; |
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raw_spin_lock_irqsave_rcu_node(rnp, flags); |
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__rcu_report_exp_rnp(rnp, wake, flags); |
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} |
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/* |
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* Report expedited quiescent state for multiple CPUs, all covered by the |
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* specified leaf rcu_node structure. |
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*/ |
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static void rcu_report_exp_cpu_mult(struct rcu_node *rnp, |
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unsigned long mask, bool wake) |
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{ |
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int cpu; |
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unsigned long flags; |
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struct rcu_data *rdp; |
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raw_spin_lock_irqsave_rcu_node(rnp, flags); |
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if (!(rnp->expmask & mask)) { |
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
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return; |
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} |
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WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask); |
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for_each_leaf_node_cpu_mask(rnp, cpu, mask) { |
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rdp = per_cpu_ptr(&rcu_data, cpu); |
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if (!IS_ENABLED(CONFIG_NO_HZ_FULL) || !rdp->rcu_forced_tick_exp) |
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continue; |
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rdp->rcu_forced_tick_exp = false; |
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tick_dep_clear_cpu(cpu, TICK_DEP_BIT_RCU_EXP); |
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} |
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__rcu_report_exp_rnp(rnp, wake, flags); /* Releases rnp->lock. */ |
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} |
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/* |
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* Report expedited quiescent state for specified rcu_data (CPU). |
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*/ |
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static void rcu_report_exp_rdp(struct rcu_data *rdp) |
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{ |
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WRITE_ONCE(rdp->cpu_no_qs.b.exp, false); |
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rcu_report_exp_cpu_mult(rdp->mynode, rdp->grpmask, true); |
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} |
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/* Common code for work-done checking. */ |
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static bool sync_exp_work_done(unsigned long s) |
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{ |
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if (rcu_exp_gp_seq_done(s)) { |
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trace_rcu_exp_grace_period(rcu_state.name, s, TPS("done")); |
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smp_mb(); /* Ensure test happens before caller kfree(). */ |
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return true; |
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} |
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return false; |
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} |
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/* |
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* Funnel-lock acquisition for expedited grace periods. Returns true |
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* if some other task completed an expedited grace period that this task |
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* can piggy-back on, and with no mutex held. Otherwise, returns false |
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* with the mutex held, indicating that the caller must actually do the |
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* expedited grace period. |
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*/ |
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static bool exp_funnel_lock(unsigned long s) |
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{ |
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struct rcu_data *rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id()); |
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struct rcu_node *rnp = rdp->mynode; |
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struct rcu_node *rnp_root = rcu_get_root(); |
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/* Low-contention fastpath. */ |
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if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) && |
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(rnp == rnp_root || |
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ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) && |
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mutex_trylock(&rcu_state.exp_mutex)) |
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goto fastpath; |
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/* |
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* Each pass through the following loop works its way up |
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* the rcu_node tree, returning if others have done the work or |
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* otherwise falls through to acquire ->exp_mutex. The mapping |
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* from CPU to rcu_node structure can be inexact, as it is just |
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* promoting locality and is not strictly needed for correctness. |
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*/ |
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for (; rnp != NULL; rnp = rnp->parent) { |
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if (sync_exp_work_done(s)) |
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return true; |
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/* Work not done, either wait here or go up. */ |
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spin_lock(&rnp->exp_lock); |
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if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) { |
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/* Someone else doing GP, so wait for them. */ |
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spin_unlock(&rnp->exp_lock); |
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trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level, |
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rnp->grplo, rnp->grphi, |
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TPS("wait")); |
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wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3], |
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sync_exp_work_done(s)); |
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return true; |
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} |
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WRITE_ONCE(rnp->exp_seq_rq, s); /* Followers can wait on us. */ |
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spin_unlock(&rnp->exp_lock); |
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trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level, |
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rnp->grplo, rnp->grphi, TPS("nxtlvl")); |
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} |
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mutex_lock(&rcu_state.exp_mutex); |
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fastpath: |
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if (sync_exp_work_done(s)) { |
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mutex_unlock(&rcu_state.exp_mutex); |
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return true; |
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} |
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rcu_exp_gp_seq_start(); |
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trace_rcu_exp_grace_period(rcu_state.name, s, TPS("start")); |
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return false; |
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} |
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/* |
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* Select the CPUs within the specified rcu_node that the upcoming |
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* expedited grace period needs to wait for. |
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*/ |
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static void sync_rcu_exp_select_node_cpus(struct work_struct *wp) |
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{ |
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int cpu; |
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unsigned long flags; |
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unsigned long mask_ofl_test; |
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unsigned long mask_ofl_ipi; |
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int ret; |
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struct rcu_exp_work *rewp = |
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container_of(wp, struct rcu_exp_work, rew_work); |
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struct rcu_node *rnp = container_of(rewp, struct rcu_node, rew); |
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raw_spin_lock_irqsave_rcu_node(rnp, flags); |
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/* Each pass checks a CPU for identity, offline, and idle. */ |
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mask_ofl_test = 0; |
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for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) { |
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struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); |
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unsigned long mask = rdp->grpmask; |
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int snap; |
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if (raw_smp_processor_id() == cpu || |
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!(rnp->qsmaskinitnext & mask)) { |
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mask_ofl_test |= mask; |
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} else { |
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snap = rcu_dynticks_snap(rdp); |
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if (rcu_dynticks_in_eqs(snap)) |
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mask_ofl_test |= mask; |
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else |
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rdp->exp_dynticks_snap = snap; |
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} |
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} |
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mask_ofl_ipi = rnp->expmask & ~mask_ofl_test; |
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/* |
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* Need to wait for any blocked tasks as well. Note that |
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* additional blocking tasks will also block the expedited GP |
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* until such time as the ->expmask bits are cleared. |
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*/ |
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if (rcu_preempt_has_tasks(rnp)) |
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WRITE_ONCE(rnp->exp_tasks, rnp->blkd_tasks.next); |
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
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|
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/* IPI the remaining CPUs for expedited quiescent state. */ |
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for_each_leaf_node_cpu_mask(rnp, cpu, mask_ofl_ipi) { |
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struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); |
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unsigned long mask = rdp->grpmask; |
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retry_ipi: |
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if (rcu_dynticks_in_eqs_since(rdp, rdp->exp_dynticks_snap)) { |
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mask_ofl_test |= mask; |
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continue; |
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} |
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if (get_cpu() == cpu) { |
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mask_ofl_test |= mask; |
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put_cpu(); |
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continue; |
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} |
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ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0); |
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put_cpu(); |
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/* The CPU will report the QS in response to the IPI. */ |
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if (!ret) |
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continue; |
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/* Failed, raced with CPU hotplug operation. */ |
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raw_spin_lock_irqsave_rcu_node(rnp, flags); |
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if ((rnp->qsmaskinitnext & mask) && |
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(rnp->expmask & mask)) { |
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/* Online, so delay for a bit and try again. */ |
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
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trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("selectofl")); |
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schedule_timeout_idle(1); |
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goto retry_ipi; |
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} |
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/* CPU really is offline, so we must report its QS. */ |
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if (rnp->expmask & mask) |
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mask_ofl_test |= mask; |
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
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} |
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/* Report quiescent states for those that went offline. */ |
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if (mask_ofl_test) |
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rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false); |
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} |
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|
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/* |
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* Select the nodes that the upcoming expedited grace period needs |
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* to wait for. |
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*/ |
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static void sync_rcu_exp_select_cpus(void) |
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{ |
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int cpu; |
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struct rcu_node *rnp; |
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|
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trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("reset")); |
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sync_exp_reset_tree(); |
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trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("select")); |
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|
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/* Schedule work for each leaf rcu_node structure. */ |
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rcu_for_each_leaf_node(rnp) { |
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rnp->exp_need_flush = false; |
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if (!READ_ONCE(rnp->expmask)) |
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continue; /* Avoid early boot non-existent wq. */ |
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if (!READ_ONCE(rcu_par_gp_wq) || |
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rcu_scheduler_active != RCU_SCHEDULER_RUNNING || |
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rcu_is_last_leaf_node(rnp)) { |
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/* No workqueues yet or last leaf, do direct call. */ |
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sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work); |
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continue; |
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} |
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INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus); |
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cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1); |
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/* If all offline, queue the work on an unbound CPU. */ |
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if (unlikely(cpu > rnp->grphi - rnp->grplo)) |
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cpu = WORK_CPU_UNBOUND; |
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else |
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cpu += rnp->grplo; |
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queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work); |
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rnp->exp_need_flush = true; |
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} |
|
|
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/* Wait for workqueue jobs (if any) to complete. */ |
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rcu_for_each_leaf_node(rnp) |
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if (rnp->exp_need_flush) |
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flush_work(&rnp->rew.rew_work); |
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} |
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|
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/* |
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* Wait for the expedited grace period to elapse, within time limit. |
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* If the time limit is exceeded without the grace period elapsing, |
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* return false, otherwise return true. |
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*/ |
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static bool synchronize_rcu_expedited_wait_once(long tlimit) |
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{ |
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int t; |
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struct rcu_node *rnp_root = rcu_get_root(); |
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|
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t = swait_event_timeout_exclusive(rcu_state.expedited_wq, |
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sync_rcu_exp_done_unlocked(rnp_root), |
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tlimit); |
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// Workqueues should not be signaled. |
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if (t > 0 || sync_rcu_exp_done_unlocked(rnp_root)) |
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return true; |
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WARN_ON(t < 0); /* workqueues should not be signaled. */ |
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return false; |
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} |
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|
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/* |
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* Wait for the expedited grace period to elapse, issuing any needed |
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* RCU CPU stall warnings along the way. |
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*/ |
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static void synchronize_rcu_expedited_wait(void) |
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{ |
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int cpu; |
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unsigned long j; |
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unsigned long jiffies_stall; |
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unsigned long jiffies_start; |
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unsigned long mask; |
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int ndetected; |
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struct rcu_data *rdp; |
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struct rcu_node *rnp; |
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struct rcu_node *rnp_root = rcu_get_root(); |
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|
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trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait")); |
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jiffies_stall = rcu_jiffies_till_stall_check(); |
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jiffies_start = jiffies; |
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if (tick_nohz_full_enabled() && rcu_inkernel_boot_has_ended()) { |
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if (synchronize_rcu_expedited_wait_once(1)) |
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return; |
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rcu_for_each_leaf_node(rnp) { |
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mask = READ_ONCE(rnp->expmask); |
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for_each_leaf_node_cpu_mask(rnp, cpu, mask) { |
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rdp = per_cpu_ptr(&rcu_data, cpu); |
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if (rdp->rcu_forced_tick_exp) |
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continue; |
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rdp->rcu_forced_tick_exp = true; |
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preempt_disable(); |
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if (cpu_online(cpu)) |
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tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP); |
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preempt_enable(); |
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} |
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} |
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j = READ_ONCE(jiffies_till_first_fqs); |
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if (synchronize_rcu_expedited_wait_once(j + HZ)) |
|
return; |
|
} |
|
|
|
for (;;) { |
|
if (synchronize_rcu_expedited_wait_once(jiffies_stall)) |
|
return; |
|
if (rcu_stall_is_suppressed()) |
|
continue; |
|
panic_on_rcu_stall(); |
|
trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall")); |
|
pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {", |
|
rcu_state.name); |
|
ndetected = 0; |
|
rcu_for_each_leaf_node(rnp) { |
|
ndetected += rcu_print_task_exp_stall(rnp); |
|
for_each_leaf_node_possible_cpu(rnp, cpu) { |
|
struct rcu_data *rdp; |
|
|
|
mask = leaf_node_cpu_bit(rnp, cpu); |
|
if (!(READ_ONCE(rnp->expmask) & mask)) |
|
continue; |
|
ndetected++; |
|
rdp = per_cpu_ptr(&rcu_data, cpu); |
|
pr_cont(" %d-%c%c%c", cpu, |
|
"O."[!!cpu_online(cpu)], |
|
"o."[!!(rdp->grpmask & rnp->expmaskinit)], |
|
"N."[!!(rdp->grpmask & rnp->expmaskinitnext)]); |
|
} |
|
} |
|
pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n", |
|
jiffies - jiffies_start, rcu_state.expedited_sequence, |
|
data_race(rnp_root->expmask), |
|
".T"[!!data_race(rnp_root->exp_tasks)]); |
|
if (ndetected) { |
|
pr_err("blocking rcu_node structures (internal RCU debug):"); |
|
rcu_for_each_node_breadth_first(rnp) { |
|
if (rnp == rnp_root) |
|
continue; /* printed unconditionally */ |
|
if (sync_rcu_exp_done_unlocked(rnp)) |
|
continue; |
|
pr_cont(" l=%u:%d-%d:%#lx/%c", |
|
rnp->level, rnp->grplo, rnp->grphi, |
|
data_race(rnp->expmask), |
|
".T"[!!data_race(rnp->exp_tasks)]); |
|
} |
|
pr_cont("\n"); |
|
} |
|
rcu_for_each_leaf_node(rnp) { |
|
for_each_leaf_node_possible_cpu(rnp, cpu) { |
|
mask = leaf_node_cpu_bit(rnp, cpu); |
|
if (!(READ_ONCE(rnp->expmask) & mask)) |
|
continue; |
|
dump_cpu_task(cpu); |
|
} |
|
} |
|
jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3; |
|
} |
|
} |
|
|
|
/* |
|
* Wait for the current expedited grace period to complete, and then |
|
* wake up everyone who piggybacked on the just-completed expedited |
|
* grace period. Also update all the ->exp_seq_rq counters as needed |
|
* in order to avoid counter-wrap problems. |
|
*/ |
|
static void rcu_exp_wait_wake(unsigned long s) |
|
{ |
|
struct rcu_node *rnp; |
|
|
|
synchronize_rcu_expedited_wait(); |
|
|
|
// Switch over to wakeup mode, allowing the next GP to proceed. |
|
// End the previous grace period only after acquiring the mutex |
|
// to ensure that only one GP runs concurrently with wakeups. |
|
mutex_lock(&rcu_state.exp_wake_mutex); |
|
rcu_exp_gp_seq_end(); |
|
trace_rcu_exp_grace_period(rcu_state.name, s, TPS("end")); |
|
|
|
rcu_for_each_node_breadth_first(rnp) { |
|
if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) { |
|
spin_lock(&rnp->exp_lock); |
|
/* Recheck, avoid hang in case someone just arrived. */ |
|
if (ULONG_CMP_LT(rnp->exp_seq_rq, s)) |
|
WRITE_ONCE(rnp->exp_seq_rq, s); |
|
spin_unlock(&rnp->exp_lock); |
|
} |
|
smp_mb(); /* All above changes before wakeup. */ |
|
wake_up_all(&rnp->exp_wq[rcu_seq_ctr(s) & 0x3]); |
|
} |
|
trace_rcu_exp_grace_period(rcu_state.name, s, TPS("endwake")); |
|
mutex_unlock(&rcu_state.exp_wake_mutex); |
|
} |
|
|
|
/* |
|
* Common code to drive an expedited grace period forward, used by |
|
* workqueues and mid-boot-time tasks. |
|
*/ |
|
static void rcu_exp_sel_wait_wake(unsigned long s) |
|
{ |
|
/* Initialize the rcu_node tree in preparation for the wait. */ |
|
sync_rcu_exp_select_cpus(); |
|
|
|
/* Wait and clean up, including waking everyone. */ |
|
rcu_exp_wait_wake(s); |
|
} |
|
|
|
/* |
|
* Work-queue handler to drive an expedited grace period forward. |
|
*/ |
|
static void wait_rcu_exp_gp(struct work_struct *wp) |
|
{ |
|
struct rcu_exp_work *rewp; |
|
|
|
rewp = container_of(wp, struct rcu_exp_work, rew_work); |
|
rcu_exp_sel_wait_wake(rewp->rew_s); |
|
} |
|
|
|
#ifdef CONFIG_PREEMPT_RCU |
|
|
|
/* |
|
* Remote handler for smp_call_function_single(). If there is an |
|
* RCU read-side critical section in effect, request that the |
|
* next rcu_read_unlock() record the quiescent state up the |
|
* ->expmask fields in the rcu_node tree. Otherwise, immediately |
|
* report the quiescent state. |
|
*/ |
|
static void rcu_exp_handler(void *unused) |
|
{ |
|
int depth = rcu_preempt_depth(); |
|
unsigned long flags; |
|
struct rcu_data *rdp = this_cpu_ptr(&rcu_data); |
|
struct rcu_node *rnp = rdp->mynode; |
|
struct task_struct *t = current; |
|
|
|
/* |
|
* First, the common case of not being in an RCU read-side |
|
* critical section. If also enabled or idle, immediately |
|
* report the quiescent state, otherwise defer. |
|
*/ |
|
if (!depth) { |
|
if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) || |
|
rcu_is_cpu_rrupt_from_idle()) { |
|
rcu_report_exp_rdp(rdp); |
|
} else { |
|
WRITE_ONCE(rdp->cpu_no_qs.b.exp, true); |
|
set_tsk_need_resched(t); |
|
set_preempt_need_resched(); |
|
} |
|
return; |
|
} |
|
|
|
/* |
|
* Second, the less-common case of being in an RCU read-side |
|
* critical section. In this case we can count on a future |
|
* rcu_read_unlock(). However, this rcu_read_unlock() might |
|
* execute on some other CPU, but in that case there will be |
|
* a future context switch. Either way, if the expedited |
|
* grace period is still waiting on this CPU, set ->deferred_qs |
|
* so that the eventual quiescent state will be reported. |
|
* Note that there is a large group of race conditions that |
|
* can have caused this quiescent state to already have been |
|
* reported, so we really do need to check ->expmask. |
|
*/ |
|
if (depth > 0) { |
|
raw_spin_lock_irqsave_rcu_node(rnp, flags); |
|
if (rnp->expmask & rdp->grpmask) { |
|
WRITE_ONCE(rdp->cpu_no_qs.b.exp, true); |
|
t->rcu_read_unlock_special.b.exp_hint = true; |
|
} |
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
|
return; |
|
} |
|
|
|
// Finally, negative nesting depth should not happen. |
|
WARN_ON_ONCE(1); |
|
} |
|
|
|
/* PREEMPTION=y, so no PREEMPTION=n expedited grace period to clean up after. */ |
|
static void sync_sched_exp_online_cleanup(int cpu) |
|
{ |
|
} |
|
|
|
/* |
|
* Scan the current list of tasks blocked within RCU read-side critical |
|
* sections, printing out the tid of each that is blocking the current |
|
* expedited grace period. |
|
*/ |
|
static int rcu_print_task_exp_stall(struct rcu_node *rnp) |
|
{ |
|
unsigned long flags; |
|
int ndetected = 0; |
|
struct task_struct *t; |
|
|
|
if (!READ_ONCE(rnp->exp_tasks)) |
|
return 0; |
|
raw_spin_lock_irqsave_rcu_node(rnp, flags); |
|
t = list_entry(rnp->exp_tasks->prev, |
|
struct task_struct, rcu_node_entry); |
|
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { |
|
pr_cont(" P%d", t->pid); |
|
ndetected++; |
|
} |
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
|
return ndetected; |
|
} |
|
|
|
#else /* #ifdef CONFIG_PREEMPT_RCU */ |
|
|
|
/* Request an expedited quiescent state. */ |
|
static void rcu_exp_need_qs(void) |
|
{ |
|
__this_cpu_write(rcu_data.cpu_no_qs.b.exp, true); |
|
/* Store .exp before .rcu_urgent_qs. */ |
|
smp_store_release(this_cpu_ptr(&rcu_data.rcu_urgent_qs), true); |
|
set_tsk_need_resched(current); |
|
set_preempt_need_resched(); |
|
} |
|
|
|
/* Invoked on each online non-idle CPU for expedited quiescent state. */ |
|
static void rcu_exp_handler(void *unused) |
|
{ |
|
struct rcu_data *rdp = this_cpu_ptr(&rcu_data); |
|
struct rcu_node *rnp = rdp->mynode; |
|
|
|
if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) || |
|
__this_cpu_read(rcu_data.cpu_no_qs.b.exp)) |
|
return; |
|
if (rcu_is_cpu_rrupt_from_idle()) { |
|
rcu_report_exp_rdp(this_cpu_ptr(&rcu_data)); |
|
return; |
|
} |
|
rcu_exp_need_qs(); |
|
} |
|
|
|
/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */ |
|
static void sync_sched_exp_online_cleanup(int cpu) |
|
{ |
|
unsigned long flags; |
|
int my_cpu; |
|
struct rcu_data *rdp; |
|
int ret; |
|
struct rcu_node *rnp; |
|
|
|
rdp = per_cpu_ptr(&rcu_data, cpu); |
|
rnp = rdp->mynode; |
|
my_cpu = get_cpu(); |
|
/* Quiescent state either not needed or already requested, leave. */ |
|
if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) || |
|
READ_ONCE(rdp->cpu_no_qs.b.exp)) { |
|
put_cpu(); |
|
return; |
|
} |
|
/* Quiescent state needed on current CPU, so set it up locally. */ |
|
if (my_cpu == cpu) { |
|
local_irq_save(flags); |
|
rcu_exp_need_qs(); |
|
local_irq_restore(flags); |
|
put_cpu(); |
|
return; |
|
} |
|
/* Quiescent state needed on some other CPU, send IPI. */ |
|
ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0); |
|
put_cpu(); |
|
WARN_ON_ONCE(ret); |
|
} |
|
|
|
/* |
|
* Because preemptible RCU does not exist, we never have to check for |
|
* tasks blocked within RCU read-side critical sections that are |
|
* blocking the current expedited grace period. |
|
*/ |
|
static int rcu_print_task_exp_stall(struct rcu_node *rnp) |
|
{ |
|
return 0; |
|
} |
|
|
|
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
|
|
|
/** |
|
* synchronize_rcu_expedited - Brute-force RCU grace period |
|
* |
|
* Wait for an RCU grace period, but expedite it. The basic idea is to |
|
* IPI all non-idle non-nohz online CPUs. The IPI handler checks whether |
|
* the CPU is in an RCU critical section, and if so, it sets a flag that |
|
* causes the outermost rcu_read_unlock() to report the quiescent state |
|
* for RCU-preempt or asks the scheduler for help for RCU-sched. On the |
|
* other hand, if the CPU is not in an RCU read-side critical section, |
|
* the IPI handler reports the quiescent state immediately. |
|
* |
|
* Although this is a great improvement over previous expedited |
|
* implementations, it is still unfriendly to real-time workloads, so is |
|
* thus not recommended for any sort of common-case code. In fact, if |
|
* you are using synchronize_rcu_expedited() in a loop, please restructure |
|
* your code to batch your updates, and then use a single synchronize_rcu() |
|
* instead. |
|
* |
|
* This has the same semantics as (but is more brutal than) synchronize_rcu(). |
|
*/ |
|
void synchronize_rcu_expedited(void) |
|
{ |
|
bool boottime = (rcu_scheduler_active == RCU_SCHEDULER_INIT); |
|
struct rcu_exp_work rew; |
|
struct rcu_node *rnp; |
|
unsigned long s; |
|
|
|
RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || |
|
lock_is_held(&rcu_lock_map) || |
|
lock_is_held(&rcu_sched_lock_map), |
|
"Illegal synchronize_rcu_expedited() in RCU read-side critical section"); |
|
|
|
/* Is the state is such that the call is a grace period? */ |
|
if (rcu_blocking_is_gp()) |
|
return; |
|
|
|
/* If expedited grace periods are prohibited, fall back to normal. */ |
|
if (rcu_gp_is_normal()) { |
|
wait_rcu_gp(call_rcu); |
|
return; |
|
} |
|
|
|
/* Take a snapshot of the sequence number. */ |
|
s = rcu_exp_gp_seq_snap(); |
|
if (exp_funnel_lock(s)) |
|
return; /* Someone else did our work for us. */ |
|
|
|
/* Ensure that load happens before action based on it. */ |
|
if (unlikely(boottime)) { |
|
/* Direct call during scheduler init and early_initcalls(). */ |
|
rcu_exp_sel_wait_wake(s); |
|
} else { |
|
/* Marshall arguments & schedule the expedited grace period. */ |
|
rew.rew_s = s; |
|
INIT_WORK_ONSTACK(&rew.rew_work, wait_rcu_exp_gp); |
|
queue_work(rcu_gp_wq, &rew.rew_work); |
|
} |
|
|
|
/* Wait for expedited grace period to complete. */ |
|
rnp = rcu_get_root(); |
|
wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3], |
|
sync_exp_work_done(s)); |
|
smp_mb(); /* Workqueue actions happen before return. */ |
|
|
|
/* Let the next expedited grace period start. */ |
|
mutex_unlock(&rcu_state.exp_mutex); |
|
|
|
if (likely(!boottime)) |
|
destroy_work_on_stack(&rew.rew_work); |
|
} |
|
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
|
|
|