rcu-tasks: *_ONCE() for rcu_tasks_cbs_head (fcb73812) · Commits · 戴 / test

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@kernel.org>

kernel/rcu/update.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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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