[tip:smp/urgent] cpu/hotplug: Adjust misplaced smb() in cpuhp_thread_fun()

[tip-bot for Neeraj Upadhyay]

Commit-ID:  f8b7530aa0a1def79c93101216b5b17cf408a70a
Gitweb:     https://git.kernel.org/tip/f8b7530aa0a1def79c93101216b5b17cf408a70a
Author:     Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
AuthorDate: Wed, 5 Sep 2018 11:22:07 +0530
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxx>
Cc: josh@xxxxxxxxxxxxxxxx
Cc: peterz@xxxxxxxxxxxxx
Cc: jiangshanlai@xxxxxxxxx
Cc: dzickus@xxxxxxxxxx
Cc: brendan.jackman@xxxxxxx
Cc: malat@xxxxxxxxxx
Cc: mojha@xxxxxxxxxxxxxx
Cc: sramana@xxxxxxxxxxxxxx
Cc: linux-arm-msm@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/1536126727-11629-1-git-send-email-neeraju@xxxxxxxxxxxxxx

---
 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) {