linux-kernel - [tip:smp/urgent] cpu/hotplug: Adjust misplaced smb() in cpuhp_thread

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Date:   Thu, 6 Sep 2018 06:51:51 -0700
From:   tip-bot for Neeraj Upadhyay <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     tglx@...utronix.de, hpa@...or.com, linux-kernel@...r.kernel.org,
        peterz@...raded.org, mingo@...nel.org, neeraju@...eaurora.org
Subject: [tip:smp/urgent] cpu/hotplug: Adjust misplaced smb() in
 cpuhp_thread_fun()

Commit-ID:  f8b7530aa0a1def79c93101216b5b17cf408a70a
Gitweb:     https://git.kernel.org/tip/f8b7530aa0a1def79c93101216b5b17cf408a70a
Author:     Neeraj Upadhyay <neeraju@...eaurora.org>
AuthorDate: Wed, 5 Sep 2018 11:22:07 +0530
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Thu, 6 Sep 2018 15:21:37 +0200

cpu/hotplug: Adjust misplaced smb() in cpuhp_thread_fun()

The smp_mb() in cpuhp_thread_fun() is misplaced. It needs 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.

Fixes: 4dddfb5faa61 ("smp/hotplug: Rewrite AP state machine core")
Signed-off-by: Neeraj Upadhyay <neeraju@...eaurora.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@...raded.org>
Cc: josh@...htriplett.org
Cc: peterz@...radead.org
Cc: jiangshanlai@...il.com
Cc: dzickus@...hat.com
Cc: brendan.jackman@....com
Cc: malat@...ian.org
Cc: mojha@...eaurora.org
Cc: sramana@...eaurora.org
Cc: linux-arm-msm@...r.kernel.org
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/1536126727-11629-1-git-send-email-neeraju@codeaurora.org

---
 kernel/cpu.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index aa7fe85ad62e..eb4041f78073 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) {