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Subject[PATCH tip/core/rcu 15/30] rcu: Add *_ONCE() to rcu_data ->rcu_forced_tick
Date
From: "Paul E. McKenney" <paulmck@kernel.org>

The rcu_data structure's ->rcu_forced_tick field is read locklessly, so
this commit adds WRITE_ONCE() to all updates and READ_ONCE() to all
lockless reads.

This data race was reported by KCSAN. Not appropriate for backporting
due to failure being unlikely.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e851a12..be59a5d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -818,11 +818,12 @@ static __always_inline void rcu_nmi_enter_common(bool irq)
incby = 1;
} 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) {
+ READ_ONCE(rdp->rcu_urgent_qs) &&
+ !READ_ONCE(rdp->rcu_forced_tick)) {
raw_spin_lock_rcu_node(rdp->mynode);
// Recheck under lock.
if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
- rdp->rcu_forced_tick = true;
+ WRITE_ONCE(rdp->rcu_forced_tick, true);
tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
}
raw_spin_unlock_rcu_node(rdp->mynode);
@@ -899,7 +900,7 @@ static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp)
WRITE_ONCE(rdp->rcu_need_heavy_qs, false);
if (tick_nohz_full_cpu(rdp->cpu) && rdp->rcu_forced_tick) {
tick_dep_clear_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
- rdp->rcu_forced_tick = false;
+ WRITE_ONCE(rdp->rcu_forced_tick, false);
}
}

--
2.9.5
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