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From: "Paul E. McKenney" <paulmck@kernel.org>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
rostedt@goodmis.org,
"Joel Fernandes (Google)" <joel@joelfernandes.org>,
Frederic Weisbecker <frederic@kernel.org>,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH rcu 4/8] rcu: Use READ_ONCE() for lockless read of rnp->qsmask
Date: Wed, 19 Oct 2022 15:46:55 -0700
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| Series |
Miscellaneous fixes for v6.2
|
|
Commit Message
Paul E. McKenney
Oct. 19, 2022, 10:46 p.m. UTC
From: "Joel Fernandes (Google)" <joel@joelfernandes.org> The rnp->qsmask is locklessly accessed from rcutree_dying_cpu(). This may help avoid load tearing due to concurrent access, KCSAN issues, and preserve sanity of people reading the mask in tracing. Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 0ca21ac0f0648..5ec97e3f7468f 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2106,7 +2106,7 @@ int rcutree_dying_cpu(unsigned int cpu) if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) return 0; - blkd = !!(rnp->qsmask & rdp->grpmask); + blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask); trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq), blkd ? TPS("cpuofl-bgp") : TPS("cpuofl")); return 0;