linux-kernel - [PATCH] cpu/hotplug: Fix acquire of st->should_run in cpuhp_thread

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Date:   Wed,  5 Sep 2018 11:22:07 +0530
From:   Neeraj Upadhyay <neeraju@...eaurora.org>
To:     tglx@...utronix.de, josh@...htriplett.org, peterz@...radead.org,
        mingo@...nel.org, jiangshanlai@...il.com, dzickus@...hat.com,
        brendan.jackman@....com, malat@...ian.org, mojha@...eaurora.org
Cc:     linux-kernel@...r.kernel.org, sramana@...eaurora.org,
        linux-arm-msm@...r.kernel.org,
        Neeraj Upadhyay <neeraju@...eaurora.org>
Subject: [PATCH] cpu/hotplug: Fix acquire of st->should_run in cpuhp_thread_fun()

The smp_mb() in cpuhp_thread_fun() appears to be misplaced, and
need to be after the load of st->should_run, to prevent
reordering of the later load/stores w.r.t. the load of
st->should_run.

Signed-off-by: Neeraj Upadhyay <neeraju@...eaurora.org>
---
 kernel/cpu.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index aa7fe85..eb4041f 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -607,15 +607,15 @@ static void cpuhp_thread_fun(unsigned int cpu)
 	bool bringup = st->bringup;
 	enum cpuhp_state state;
 
+	if (WARN_ON_ONCE(!st->should_run))
+		return;
+
 	/*
 	 * ACQUIRE for the cpuhp_should_run() load of ->should_run. Ensures
 	 * that if we see ->should_run we also see the rest of the state.
 	 */
 	smp_mb();
 
-	if (WARN_ON_ONCE(!st->should_run))
-		return;
-
 	cpuhp_lock_acquire(bringup);
 
 	if (st->single) {
-- 
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