From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, rushikesh.s.kadam@intel.com,
urezki@gmail.com, neeraj.iitr10@gmail.com, frederic@kernel.org,
paulmck@kernel.org, rostedt@goodmis.org,
"Joel Fernandes (Google)" <joel@joelfernandes.org>
Subject: [PATCH rcu/next 1/3] rcu/tree: Use READ_ONCE() for lockless read of rnp->qsmask
Date: Sat, 17 Sep 2022 16:41:58 +0000 [thread overview]
Message-ID: <20220917164200.511783-2-joel@joelfernandes.org> (raw)
In-Reply-To: <20220917164200.511783-1-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>
---
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 0ca21ac0f064..5ec97e3f7468 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;
--
2.37.3.968.ga6b4b080e4-goog
next prev parent reply other threads:[~2022-09-17 16:42 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-17 16:41 [PATCH rcu/next 0/3] Preparatory patches borrowed from lazy rcu v5 Joel Fernandes (Google)
2022-09-17 16:41 ` Joel Fernandes (Google) [this message]
2022-09-17 16:41 ` [PATCH rcu/next 2/3] rcu: Fix late wakeup when flush of bypass cblist happens (v6) Joel Fernandes (Google)
2022-09-21 14:54 ` Paul E. McKenney
2022-09-17 16:42 ` [PATCH rcu/next 3/3] rcu: Call trace_rcu_callback() also for bypass queuing (v2) Joel Fernandes (Google)
2022-09-17 19:58 ` Frederic Weisbecker
2022-09-17 21:43 ` Joel Fernandes
2022-09-17 22:21 ` Frederic Weisbecker
2022-09-17 22:42 ` Joel Fernandes
-- strict thread matches above, loose matches on Subject: below --
2022-09-15 0:14 [PATCH rcu/next 0/3] Preparatory patches borrowed from lazy rcu v5 Joel Fernandes (Google)
2022-09-15 0:14 ` [PATCH rcu/next 1/3] rcu/tree: Use READ_ONCE() for lockless read of rnp->qsmask Joel Fernandes (Google)
2022-09-16 10:55 ` Frederic Weisbecker
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