Commit 24bb9ecc authored Dec 22, 2019 by Paul E. McKenney

rcu: Fix exp_funnel_lock()/rcu_exp_wait_wake() datarace



The rcu_node structure's ->exp_seq_rq field is accessed locklessly, so
updates must use WRITE_ONCE().  This commit therefore adds the needed
WRITE_ONCE() invocation where it was missed.

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>

parent 82dd8419

kernel/rcu/tree_exp.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -589,7 +589,7 @@ static void rcu_exp_wait_wake(unsigned long s)
		spin_lock(&rnp->exp_lock);
		/* Recheck, avoid hang in case someone just arrived. */
		if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
		rnp->exp_seq_rq = s;
		WRITE_ONCE(rnp->exp_seq_rq, s);
		spin_unlock(&rnp->exp_lock);
		}
		smp_mb(); /* All above changes before wakeup. */

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