From: Paul E. McKenney <paulmck@kernel.org>
Date: Fri, 3 Jan 2020 20:12:06 +0000 (-0800)
Subject: rcu: Add WRITE_ONCE to rcu_node ->exp_seq_rq store
X-Git-Url: http://git.osdn.net/view?a=commitdiff_plain;h=b0c18c87730a4de6da0303fa99aea43e814233f9;p=uclinux-h8%2Flinux.git

rcu: Add WRITE_ONCE to rcu_node ->exp_seq_rq store

The rcu_node structure's ->exp_seq_rq field is read locklessly, so
this commit adds the WRITE_ONCE() to a load in order to provide proper
documentation and READ_ONCE()/WRITE_ONCE() pairing.

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>
---

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index d7e04849c7ab..85b009e05637 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -314,7 +314,7 @@ static bool exp_funnel_lock(unsigned long s)
 				   sync_exp_work_done(s));
 			return true;
 		}
-		rnp->exp_seq_rq = s; /* Followers can wait on us. */
+		WRITE_ONCE(rnp->exp_seq_rq, s); /* Followers can wait on us. */
 		spin_unlock(&rnp->exp_lock);
 		trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
 					  rnp->grplo, rnp->grphi, TPS("nxtlvl"));