The following commit has been merged into the core/rcu branch of tip:
Commit-ID: 5b14557b073c96a7cf79adc4d7b6c4a8c26b2a43
Gitweb: https://git.kernel.org/tip/5b14557b073c96a7cf79adc4d7b6c4a8c26b2a43
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate: Tue, 26 Nov 2019 18:05:45 -08:00
Committer: Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Fri, 24 Jan 2020 10:27:33 -08:00
rcu: Avoid tick_dep_set_cpu() misordering
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@xxxxxxxxxx>
---
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) {
|