/* 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 <paulmck@linux.ibm.com>
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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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* 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->exp_deferred_qs, 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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/* 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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* 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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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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/* 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))
|
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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}
|
|
/* Wait for workqueue jobs (if any) to complete. */
|
rcu_for_each_leaf_node(rnp)
|
if (rnp->exp_need_flush)
|
flush_work(&rnp->rew.rew_work);
|
}
|
|
/*
|
* Wait for the expedited grace period to elapse, within time limit.
|
* If the time limit is exceeded without the grace period elapsing,
|
* return false, otherwise return true.
|
*/
|
static bool synchronize_rcu_expedited_wait_once(long tlimit)
|
{
|
int t;
|
struct rcu_node *rnp_root = rcu_get_root();
|
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t = swait_event_timeout_exclusive(rcu_state.expedited_wq,
|
sync_rcu_exp_done_unlocked(rnp_root),
|
tlimit);
|
// Workqueues should not be signaled.
|
if (t > 0 || sync_rcu_exp_done_unlocked(rnp_root))
|
return true;
|
WARN_ON(t < 0); /* workqueues should not be signaled. */
|
return false;
|
}
|
|
/*
|
* Wait for the expedited grace period to elapse, issuing any needed
|
* RCU CPU stall warnings along the way.
|
*/
|
static void synchronize_rcu_expedited_wait(void)
|
{
|
int cpu;
|
unsigned long j;
|
unsigned long jiffies_stall;
|
unsigned long jiffies_start;
|
unsigned long mask;
|
int ndetected;
|
struct rcu_data *rdp;
|
struct rcu_node *rnp;
|
struct rcu_node *rnp_root = rcu_get_root();
|
|
trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait"));
|
jiffies_stall = rcu_jiffies_till_stall_check();
|
jiffies_start = jiffies;
|
if (tick_nohz_full_enabled() && rcu_inkernel_boot_has_ended()) {
|
if (synchronize_rcu_expedited_wait_once(1))
|
return;
|
rcu_for_each_leaf_node(rnp) {
|
for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) {
|
rdp = per_cpu_ptr(&rcu_data, cpu);
|
if (rdp->rcu_forced_tick_exp)
|
continue;
|
rdp->rcu_forced_tick_exp = true;
|
tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
|
}
|
}
|
j = READ_ONCE(jiffies_till_first_fqs);
|
if (synchronize_rcu_expedited_wait_once(j + HZ))
|
return;
|
WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT));
|
}
|
|
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:");
|
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_dynticks_curr_cpu_in_eqs()) {
|
rcu_report_exp_rdp(rdp);
|
} else {
|
rdp->exp_deferred_qs = 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) {
|
rdp->exp_deferred_qs = 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) ||
|
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 no_wq;
|
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. */
|
|
/* Don't use workqueue during boot or from an incoming CPU. */
|
preempt_disable();
|
no_wq = rcu_scheduler_active == RCU_SCHEDULER_INIT ||
|
!cpumask_test_cpu(smp_processor_id(), cpu_active_mask);
|
preempt_enable();
|
|
/* Ensure that load happens before action based on it. */
|
if (unlikely(no_wq)) {
|
/* Direct call for scheduler init, early_initcall()s, and incoming CPUs. */
|
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(!no_wq))
|
destroy_work_on_stack(&rew.rew_work);
|
}
|
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
|
