812 lines
25 KiB
C
812 lines
25 KiB
C
/*
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* RCU expedited grace periods
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, you can access it online at
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* http://www.gnu.org/licenses/gpl-2.0.html.
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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.vnet.ibm.com>
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*/
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#include <linux/lockdep.h>
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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(struct rcu_state *rsp)
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{
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rcu_seq_start(&rsp->expedited_sequence);
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}
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/*
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* Return then value that 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(struct rcu_state *rsp)
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{
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return rcu_seq_endval(&rsp->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(struct rcu_state *rsp)
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{
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rcu_seq_end(&rsp->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.
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*/
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static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp)
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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(&rsp->expedited_sequence);
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trace_rcu_exp_grace_period(rsp->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(struct rcu_state *rsp, unsigned long s)
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{
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return rcu_seq_done(&rsp->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(struct rcu_state *rsp)
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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(&rsp->ncpus); /* Order against 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 == rsp->ncpus_snap))
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return;
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rsp->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(rsp, 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(struct rcu_state *rsp)
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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(rsp);
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rcu_for_each_node_breadth_first(rsp, 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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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. Works only for preemptible
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* RCU -- other RCU implementation use other means.
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*
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* Caller must hold the specificed rcu_node structure's ->lock
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*/
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static bool sync_rcu_preempt_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 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_preempt_exp_done(), but this function assumes the caller
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* doesn't hold the rcu_node's ->lock, and will acquire and release the lock
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* itself
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*/
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static bool sync_rcu_preempt_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_preempt_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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* Caller must hold the specified rcu_node structure's ->lock.
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*/
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static void __rcu_report_exp_rnp(struct rcu_state *rsp, 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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for (;;) {
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if (!sync_rcu_preempt_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(&rsp->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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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_state *rsp,
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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(rsp, 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_state *rsp, struct rcu_node *rnp,
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unsigned long mask, 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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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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rnp->expmask &= ~mask;
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__rcu_report_exp_rnp(rsp, 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_state *rsp, struct rcu_data *rdp,
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bool wake)
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{
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rcu_report_exp_cpu_mult(rsp, rdp->mynode, rdp->grpmask, wake);
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}
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/* Common code for synchronize_{rcu,sched}_expedited() work-done checking. */
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static bool sync_exp_work_done(struct rcu_state *rsp, unsigned long s)
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{
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if (rcu_exp_gp_seq_done(rsp, s)) {
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trace_rcu_exp_grace_period(rsp->name, s, TPS("done"));
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/* Ensure test happens before caller kfree(). */
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smp_mb__before_atomic(); /* ^^^ */
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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(struct rcu_state *rsp, unsigned long s)
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{
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struct rcu_data *rdp = per_cpu_ptr(rsp->rda, 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(rsp);
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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(&rsp->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 rsp->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(rsp, 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(rsp->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(rsp, s));
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return true;
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}
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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(rsp->name, rnp->level, rnp->grplo,
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rnp->grphi, TPS("nxtlvl"));
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}
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mutex_lock(&rsp->exp_mutex);
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fastpath:
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if (sync_exp_work_done(rsp, s)) {
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mutex_unlock(&rsp->exp_mutex);
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return true;
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}
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rcu_exp_gp_seq_start(rsp);
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trace_rcu_exp_grace_period(rsp->name, s, TPS("start"));
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return false;
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}
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/* Invoked on each online non-idle CPU for expedited quiescent state. */
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static void sync_sched_exp_handler(void *data)
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{
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struct rcu_data *rdp;
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struct rcu_node *rnp;
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struct rcu_state *rsp = data;
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rdp = this_cpu_ptr(rsp->rda);
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rnp = rdp->mynode;
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if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
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__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
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return;
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if (rcu_is_cpu_rrupt_from_idle()) {
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rcu_report_exp_rdp(&rcu_sched_state,
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this_cpu_ptr(&rcu_sched_data), true);
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return;
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}
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__this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true);
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/* Store .exp before .rcu_urgent_qs. */
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smp_store_release(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs), true);
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resched_cpu(smp_processor_id());
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}
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/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
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static void sync_sched_exp_online_cleanup(int cpu)
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{
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struct rcu_data *rdp;
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int ret;
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struct rcu_node *rnp;
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struct rcu_state *rsp = &rcu_sched_state;
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rdp = per_cpu_ptr(rsp->rda, cpu);
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rnp = rdp->mynode;
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if (!(READ_ONCE(rnp->expmask) & rdp->grpmask))
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return;
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ret = smp_call_function_single(cpu, sync_sched_exp_handler, rsp, 0);
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WARN_ON_ONCE(ret);
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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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smp_call_func_t func;
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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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struct rcu_state *rsp = rewp->rew_rsp;
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func = rewp->rew_func;
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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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unsigned long mask = leaf_node_cpu_bit(rnp, cpu);
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struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
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struct rcu_dynticks *rdtp = per_cpu_ptr(&rcu_dynticks, cpu);
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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(rdtp);
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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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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, rnp->expmask) {
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unsigned long mask = leaf_node_cpu_bit(rnp, cpu);
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struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
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if (!(mask_ofl_ipi & mask))
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continue;
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retry_ipi:
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if (rcu_dynticks_in_eqs_since(rdp->dynticks,
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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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ret = smp_call_function_single(cpu, func, rsp, 0);
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if (!ret) {
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mask_ofl_ipi &= ~mask;
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continue;
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}
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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(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("selectofl"));
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schedule_timeout_uninterruptible(1);
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goto retry_ipi;
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}
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/* CPU really is offline, so we can ignore it. */
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if (!(rnp->expmask & mask))
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mask_ofl_ipi &= ~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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mask_ofl_test |= mask_ofl_ipi;
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if (mask_ofl_test)
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rcu_report_exp_cpu_mult(rsp, rnp, mask_ofl_test, false);
|
|
}
|
|
|
|
/*
|
|
* Select the nodes that the upcoming expedited grace period needs
|
|
* to wait for.
|
|
*/
|
|
static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
|
|
smp_call_func_t func)
|
|
{
|
|
int cpu;
|
|
struct rcu_node *rnp;
|
|
|
|
trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("reset"));
|
|
sync_exp_reset_tree(rsp);
|
|
trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("select"));
|
|
|
|
/* Schedule work for each leaf rcu_node structure. */
|
|
rcu_for_each_leaf_node(rsp, rnp) {
|
|
rnp->exp_need_flush = false;
|
|
if (!READ_ONCE(rnp->expmask))
|
|
continue; /* Avoid early boot non-existent wq. */
|
|
rnp->rew.rew_func = func;
|
|
rnp->rew.rew_rsp = rsp;
|
|
if (!READ_ONCE(rcu_par_gp_wq) ||
|
|
rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
|
|
rcu_is_last_leaf_node(rsp, rnp)) {
|
|
/* No workqueues yet or last leaf, do direct call. */
|
|
sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work);
|
|
continue;
|
|
}
|
|
INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
|
|
preempt_disable();
|
|
cpu = cpumask_next(rnp->grplo - 1, cpu_online_mask);
|
|
/* If all offline, queue the work on an unbound CPU. */
|
|
if (unlikely(cpu > rnp->grphi))
|
|
cpu = WORK_CPU_UNBOUND;
|
|
queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
|
|
preempt_enable();
|
|
rnp->exp_need_flush = true;
|
|
}
|
|
|
|
/* Wait for workqueue jobs (if any) to complete. */
|
|
rcu_for_each_leaf_node(rsp, rnp)
|
|
if (rnp->exp_need_flush)
|
|
flush_work(&rnp->rew.rew_work);
|
|
}
|
|
|
|
static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
|
|
{
|
|
int cpu;
|
|
unsigned long jiffies_stall;
|
|
unsigned long jiffies_start;
|
|
unsigned long mask;
|
|
int ndetected;
|
|
struct rcu_node *rnp;
|
|
struct rcu_node *rnp_root = rcu_get_root(rsp);
|
|
int ret;
|
|
|
|
trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("startwait"));
|
|
jiffies_stall = rcu_jiffies_till_stall_check();
|
|
jiffies_start = jiffies;
|
|
|
|
for (;;) {
|
|
ret = swait_event_timeout_exclusive(
|
|
rsp->expedited_wq,
|
|
sync_rcu_preempt_exp_done_unlocked(rnp_root),
|
|
jiffies_stall);
|
|
if (ret > 0 || sync_rcu_preempt_exp_done_unlocked(rnp_root))
|
|
return;
|
|
WARN_ON(ret < 0); /* workqueues should not be signaled. */
|
|
if (rcu_cpu_stall_suppress)
|
|
continue;
|
|
panic_on_rcu_stall();
|
|
pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
|
|
rsp->name);
|
|
ndetected = 0;
|
|
rcu_for_each_leaf_node(rsp, 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 (!(rnp->expmask & mask))
|
|
continue;
|
|
ndetected++;
|
|
rdp = per_cpu_ptr(rsp->rda, 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, rsp->expedited_sequence,
|
|
rnp_root->expmask, ".T"[!!rnp_root->exp_tasks]);
|
|
if (ndetected) {
|
|
pr_err("blocking rcu_node structures:");
|
|
rcu_for_each_node_breadth_first(rsp, rnp) {
|
|
if (rnp == rnp_root)
|
|
continue; /* printed unconditionally */
|
|
if (sync_rcu_preempt_exp_done_unlocked(rnp))
|
|
continue;
|
|
pr_cont(" l=%u:%d-%d:%#lx/%c",
|
|
rnp->level, rnp->grplo, rnp->grphi,
|
|
rnp->expmask,
|
|
".T"[!!rnp->exp_tasks]);
|
|
}
|
|
pr_cont("\n");
|
|
}
|
|
rcu_for_each_leaf_node(rsp, rnp) {
|
|
for_each_leaf_node_possible_cpu(rnp, cpu) {
|
|
mask = leaf_node_cpu_bit(rnp, cpu);
|
|
if (!(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(struct rcu_state *rsp, unsigned long s)
|
|
{
|
|
struct rcu_node *rnp;
|
|
|
|
synchronize_sched_expedited_wait(rsp);
|
|
rcu_exp_gp_seq_end(rsp);
|
|
trace_rcu_exp_grace_period(rsp->name, s, TPS("end"));
|
|
|
|
/*
|
|
* Switch over to wakeup mode, allowing the next GP, but -only- the
|
|
* next GP, to proceed.
|
|
*/
|
|
mutex_lock(&rsp->exp_wake_mutex);
|
|
|
|
rcu_for_each_node_breadth_first(rsp, 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))
|
|
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(rsp->expedited_sequence) & 0x3]);
|
|
}
|
|
trace_rcu_exp_grace_period(rsp->name, s, TPS("endwake"));
|
|
mutex_unlock(&rsp->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(struct rcu_state *rsp,
|
|
smp_call_func_t func, unsigned long s)
|
|
{
|
|
/* Initialize the rcu_node tree in preparation for the wait. */
|
|
sync_rcu_exp_select_cpus(rsp, func);
|
|
|
|
/* Wait and clean up, including waking everyone. */
|
|
rcu_exp_wait_wake(rsp, 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_rsp, rewp->rew_func, rewp->rew_s);
|
|
}
|
|
|
|
/*
|
|
* Given an rcu_state pointer and a smp_call_function() handler, kick
|
|
* off the specified flavor of expedited grace period.
|
|
*/
|
|
static void _synchronize_rcu_expedited(struct rcu_state *rsp,
|
|
smp_call_func_t func)
|
|
{
|
|
struct rcu_data *rdp;
|
|
struct rcu_exp_work rew;
|
|
struct rcu_node *rnp;
|
|
unsigned long s;
|
|
|
|
/* If expedited grace periods are prohibited, fall back to normal. */
|
|
if (rcu_gp_is_normal()) {
|
|
wait_rcu_gp(rsp->call);
|
|
return;
|
|
}
|
|
|
|
/* Take a snapshot of the sequence number. */
|
|
s = rcu_exp_gp_seq_snap(rsp);
|
|
if (exp_funnel_lock(rsp, s))
|
|
return; /* Someone else did our work for us. */
|
|
|
|
/* Ensure that load happens before action based on it. */
|
|
if (unlikely(rcu_scheduler_active == RCU_SCHEDULER_INIT)) {
|
|
/* Direct call during scheduler init and early_initcalls(). */
|
|
rcu_exp_sel_wait_wake(rsp, func, s);
|
|
} else {
|
|
/* Marshall arguments & schedule the expedited grace period. */
|
|
rew.rew_func = func;
|
|
rew.rew_rsp = rsp;
|
|
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. */
|
|
rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());
|
|
rnp = rcu_get_root(rsp);
|
|
wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
|
|
sync_exp_work_done(rsp, s));
|
|
smp_mb(); /* Workqueue actions happen before return. */
|
|
|
|
/* Let the next expedited grace period start. */
|
|
mutex_unlock(&rsp->exp_mutex);
|
|
}
|
|
|
|
/**
|
|
* synchronize_sched_expedited - Brute-force RCU-sched grace period
|
|
*
|
|
* Wait for an RCU-sched grace period to elapse, but use a "big hammer"
|
|
* approach to force the grace period to end quickly. This consumes
|
|
* significant time on all CPUs and is unfriendly to real-time workloads,
|
|
* so is thus not recommended for any sort of common-case code. In fact,
|
|
* if you are using synchronize_sched_expedited() in a loop, please
|
|
* restructure your code to batch your updates, and then use a single
|
|
* synchronize_sched() instead.
|
|
*
|
|
* This implementation can be thought of as an application of sequence
|
|
* locking to expedited grace periods, but using the sequence counter to
|
|
* determine when someone else has already done the work instead of for
|
|
* retrying readers.
|
|
*/
|
|
void synchronize_sched_expedited(void)
|
|
{
|
|
struct rcu_state *rsp = &rcu_sched_state;
|
|
|
|
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_sched_expedited() in RCU read-side critical section");
|
|
|
|
/* If only one CPU, this is automatically a grace period. */
|
|
if (rcu_blocking_is_gp())
|
|
return;
|
|
|
|
_synchronize_rcu_expedited(rsp, sync_sched_exp_handler);
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
|
|
|
|
#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 sync_rcu_exp_handler(void *info)
|
|
{
|
|
struct rcu_data *rdp;
|
|
struct rcu_state *rsp = info;
|
|
struct task_struct *t = current;
|
|
|
|
/*
|
|
* Within an RCU read-side critical section, request that the next
|
|
* rcu_read_unlock() report. Unless this RCU read-side critical
|
|
* section has already blocked, in which case it is already set
|
|
* up for the expedited grace period to wait on it.
|
|
*/
|
|
if (t->rcu_read_lock_nesting > 0 &&
|
|
!t->rcu_read_unlock_special.b.blocked) {
|
|
t->rcu_read_unlock_special.b.exp_need_qs = true;
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* We are either exiting an RCU read-side critical section (negative
|
|
* values of t->rcu_read_lock_nesting) or are not in one at all
|
|
* (zero value of t->rcu_read_lock_nesting). Or we are in an RCU
|
|
* read-side critical section that blocked before this expedited
|
|
* grace period started. Either way, we can immediately report
|
|
* the quiescent state.
|
|
*/
|
|
rdp = this_cpu_ptr(rsp->rda);
|
|
rcu_report_exp_rdp(rsp, rdp, true);
|
|
}
|
|
|
|
/**
|
|
* synchronize_rcu_expedited - Brute-force RCU grace period
|
|
*
|
|
* Wait for an RCU-preempt 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-preempt critical section, and
|
|
* if so, it sets a flag that causes the outermost rcu_read_unlock()
|
|
* to report the quiescent state. 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 greate 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.
|
|
*/
|
|
void synchronize_rcu_expedited(void)
|
|
{
|
|
struct rcu_state *rsp = rcu_state_p;
|
|
|
|
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");
|
|
|
|
if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
|
|
return;
|
|
_synchronize_rcu_expedited(rsp, sync_rcu_exp_handler);
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
|
|
|
|
#else /* #ifdef CONFIG_PREEMPT_RCU */
|
|
|
|
/*
|
|
* Wait for an rcu-preempt grace period, but make it happen quickly.
|
|
* But because preemptible RCU does not exist, map to rcu-sched.
|
|
*/
|
|
void synchronize_rcu_expedited(void)
|
|
{
|
|
synchronize_sched_expedited();
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
|
|
|
|
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
|