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authorPaul E. McKenney <paulmck@kernel.org>2019-11-26 18:05:45 -0800
committerPaul E. McKenney <paulmck@kernel.org>2020-01-24 10:27:33 -0800
commit5b14557b073c96a7cf79adc4d7b6c4a8c26b2a43 (patch)
tree4c4590af8b9c59b6408350d387c5aed3c4e76204 /kernel
parent77339e61aa309310a535bd01eb3388f7a27b36f9 (diff)
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@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/rcu/tree.c12
1 files changed, 9 insertions, 3 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 5445da2326a0..b0e0612392a9 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) {