The following commit has been merged into the core/rcu branch of tip: Commit-ID: fcb7381265e6cceb1d54283878d145db52b9d9d7 Gitweb: https://git.kernel.org/tip/fcb7381265e6cceb1d54283878d145db52b9d9d7 Author: Paul E. McKenney <paulmck@xxxxxxxxxx> AuthorDate: Mon, 06 Jan 2020 11:59:58 -08:00 Committer: Paul E. McKenney <paulmck@xxxxxxxxxx> CommitterDate: Thu, 20 Feb 2020 16:00:45 -08:00 rcu-tasks: *_ONCE() for rcu_tasks_cbs_head The RCU tasks list of callbacks, rcu_tasks_cbs_head, is sampled locklessly by rcu_tasks_kthread() when waiting for work to do. This commit therefore applies READ_ONCE() to that lockless sampling and WRITE_ONCE() to the single potential store outside of rcu_tasks_kthread. This data race was reported by KCSAN. Not appropriate for backporting due to failure being unlikely. Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> --- kernel/rcu/update.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index 6c4b862..a27df76 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -528,7 +528,7 @@ void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func) rhp->func = func; raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags); needwake = !rcu_tasks_cbs_head; - *rcu_tasks_cbs_tail = rhp; + WRITE_ONCE(*rcu_tasks_cbs_tail, rhp); rcu_tasks_cbs_tail = &rhp->next; raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags); /* We can't create the thread unless interrupts are enabled. */ @@ -658,7 +658,7 @@ static int __noreturn rcu_tasks_kthread(void *arg) /* If there were none, wait a bit and start over. */ if (!list) { wait_event_interruptible(rcu_tasks_cbs_wq, - rcu_tasks_cbs_head); + READ_ONCE(rcu_tasks_cbs_head)); if (!rcu_tasks_cbs_head) { WARN_ON(signal_pending(current)); schedule_timeout_interruptible(HZ/10);
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