From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 11/11] rcu: Avoid tick_dep_set_cpu() misordering
Date: Mon, 9 Dec 2019 20:26:29 -0800 [thread overview]
Message-ID: <20191210042629.3808-11-paulmck@kernel.org> (raw)
In-Reply-To: <20191210042606.GA3624@paulmck-ThinkPad-P72>
From: "Paul E. McKenney" <paulmck@kernel.org>
In the current code, rcu_nmi_enter_common() might decide to turn on
the tick using tick_dep_set_cpu(), but be delayed just before doing so.
Then the grace-period kthread might notice that the CPU in question had
in fact gone through a quiescent state, thus turning off the tick using
tick_dep_clear_cpu(). The later invocation of tick_dep_set_cpu() would
then incorrectly leave the tick on.
This commit therefore enlists the aid of the leaf rcu_node structure's
->lock to ensure that decisions to enable or disable the tick are
carried out before they can be reversed.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 5445da2..b0e0612 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -800,8 +800,8 @@ void rcu_user_exit(void)
*/
static __always_inline void rcu_nmi_enter_common(bool irq)
{
- struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
long incby = 2;
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
/* Complain about underflow. */
WARN_ON_ONCE(rdp->dynticks_nmi_nesting < 0);
@@ -828,8 +828,13 @@ static __always_inline void rcu_nmi_enter_common(bool irq)
} else if (tick_nohz_full_cpu(rdp->cpu) &&
rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE &&
READ_ONCE(rdp->rcu_urgent_qs) && !rdp->rcu_forced_tick) {
- rdp->rcu_forced_tick = true;
- tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
+ raw_spin_lock_rcu_node(rdp->mynode);
+ // Recheck under lock.
+ if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
+ rdp->rcu_forced_tick = true;
+ tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
+ }
+ raw_spin_unlock_rcu_node(rdp->mynode);
}
trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
rdp->dynticks_nmi_nesting,
@@ -898,6 +903,7 @@ void rcu_irq_enter_irqson(void)
*/
static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp)
{
+ raw_lockdep_assert_held_rcu_node(rdp->mynode);
WRITE_ONCE(rdp->rcu_urgent_qs, false);
WRITE_ONCE(rdp->rcu_need_heavy_qs, false);
if (tick_nohz_full_cpu(rdp->cpu) && rdp->rcu_forced_tick) {
--
2.9.5
prev parent reply other threads:[~2019-12-10 4:26 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-10 4:26 [PATCH tip/core/rcu 0/11] Preemptible-RCU updates for v5.6 Paul E. McKenney
2019-12-10 4:26 ` [PATCH tip/core/rcu 01/11] rcu/nocb: Fix dump_tree hierarchy print always active paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 02/11] rcu: Avoid data-race in rcu_gp_fqs_check_wake() paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 03/11] rcu: Use lockdep rather than comment to enforce lock held paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 04/11] rcu: Make PREEMPT_RCU be a modifier to TREE_RCU paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 05/11] rcu: Use CONFIG_PREEMPTION where appropriate paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 06/11] rcu: Rename some instance of CONFIG_PREEMPTION to CONFIG_PREEMPT_RCU paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 07/11] rcu: Clear .exp_hint only when deferred quiescent state has been reported paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 08/11] rcu: Clear ->rcu_read_unlock_special only once paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 09/11] rcu: Use READ_ONCE() for ->expmask in rcu_read_unlock_special() paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 10/11] rcu: Provide wrappers for uses of ->rcu_read_lock_nesting paulmck
2019-12-10 4:26 ` paulmck [this message]
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