[tip/core/rcu,03/30] rcu: Fix exp_funnel_lock()/rcu_exp_wait_wake() datarace
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Message ID 20200214235607.13749-3-paulmck@kernel.org
State In Next
Commit a1ba95e1ce7c87ac18948616cefc25140ccd9e7b
Headers show
  • Miscellaneous fixes for v5.7
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Commit Message

Paul E. McKenney Feb. 14, 2020, 11:55 p.m. UTC
From: "Paul E. McKenney" <paulmck@kernel.org>

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>
 kernel/rcu/tree_exp.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index dcbd757..d7e0484 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -589,7 +589,7 @@  static void rcu_exp_wait_wake(unsigned long s)
 			/* 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);
 		smp_mb(); /* All above changes before wakeup. */