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[tip:locking/core] futex: Use smp_store_release() in mark_wake_futex()

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Commit-ID:  1b367ece0d7e696cab1c8501bab282cc6a538b3f
Gitweb:     http://git.kernel.org/tip/1b367ece0d7e696cab1c8501bab282cc6a538b3f
Author:     Peter Zijlstra <peterz@infradead.org>
AuthorDate: Wed, 22 Mar 2017 11:35:49 +0100
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 23 Mar 2017 19:10:06 +0100

futex: Use smp_store_release() in mark_wake_futex()

Since the futex_q can dissapear the instruction after assigning NULL,
this really should be a RELEASE barrier. That stops loads from hitting
dead memory too.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104151.604296452@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 kernel/futex.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 1531cc4..cc10340 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1290,8 +1290,7 @@ static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
 	 * memory barrier is required here to prevent the following
 	 * store to lock_ptr from getting ahead of the plist_del.
 	 */
-	smp_wmb();
-	q->lock_ptr = NULL;
+	smp_store_release(&q->lock_ptr, NULL);
 }
 
 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *top_waiter,

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[PATCH -v6 00/13] The arduous story of FUTEX_UNLOCK_PI Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
  [PATCH -v6 10/13] futex,rt_mutex: Restructure rt_mutex_finish_proxy_lock() Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex,rt_mutex: Restructure  rt_mutex_finish_proxy_lock() tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 07/13] futex: Rework inconsistent rt_mutex/futex_q state Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Rework inconsistent rt_mutex/futex_q  state tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 09/13] futex,rt_mutex: Introduce rt_mutex_init_waiter() Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex,rt_mutex: Introduce rt_mutex_init_waiter() tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 05/13] futex: Change locking rules Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Change locking rules tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 11/13] futex: Rework futex_lock_pi() to use rt_mutex_*_proxy_lock() Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Rework futex_lock_pi() to use  rt_mutex_*_proxy_lock() tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 13/13] futex: futex_lock_pi() vs PREEMPT_RT_FULL Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Drop hb->lock before enqueueing on the  rtmutex tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 03/13] futex: Remove rt_mutex_deadlock_account_*() Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Remove rt_mutex_deadlock_account_*() tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
    Re: [PATCH -v6 03/13] futex: Remove rt_mutex_deadlock_account_*() Darren Hart <dvhart@infradead.org> - 2017-03-24 22:30 +0100
      Re: [PATCH -v6 03/13] futex: Remove rt_mutex_deadlock_account_*() Darren Hart <dvhart@infradead.org> - 2017-03-24 22:40 +0100
  [PATCH -v6 12/13] futex: futex_unlock_pi() determinism Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Futex_unlock_pi() determinism tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 06/13] futex: Cleanup refcounting Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Cleanup refcounting tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
  [PATCH -v6 04/13] futex,rt_mutex: Provide futex specific rt_mutex API Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex,rt_mutex: Provide futex specific rt_mutex  API tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
    Re: [PATCH -v6 04/13] futex,rt_mutex: Provide futex specific  rt_mutex API Darren Hart <dvhart@infradead.org> - 2017-03-25 01:40 +0100
  [PATCH -v6 02/13] futex: Use smp_store_release() in mark_wake_futex() Peter Zijlstra <peterz@infradead.org> - 2017-03-22 11:50 +0100
    [tip:locking/core] futex: Use smp_store_release() in  mark_wake_futex() tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-03-23 19:30 +0100
    Re: [PATCH -v6 02/13] futex: Use smp_store_release() in  mark_wake_futex() Darren Hart <dvhart@infradead.org> - 2017-03-24 22:20 +0100
  Re: [PATCH -v6 00/13] The arduous story of FUTEX_UNLOCK_PI Darren Hart <dvhart@infradead.org> - 2017-03-24 02:50 +0100

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