From: Darren Hart <dvhart@infradead.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: tglx@linutronix.de, mingo@kernel.org, juri.lelli@arm.com,
rostedt@goodmis.org, xlpang@redhat.com, bigeasy@linutronix.de,
linux-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com,
jdesfossez@efficios.com, bristot@redhat.com
Subject: Re: [PATCH -v6 02/13] futex: Use smp_store_release() in mark_wake_futex()
Date: Fri, 24 Mar 2017 14:16:22 -0700 [thread overview]
Message-ID: <20170324211622.GB18290@fury> (raw)
In-Reply-To: <20170322104151.604296452@infradead.org>
On Wed, Mar 22, 2017 at 11:35:49AM +0100, Peter Zijlstra wrote:
> 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>
I reviewed this carefully in the previous thread, confirming that despite the
move to wake queues, spurious wakeups can still lead to the situration Peter
describes. As such:
Reviewed-by: Darren Hart (VMware) <dvhart@infradead.org>
My only suggestion would be to clarify the language in the preceding comment to
make that obvious, as well as clarify which plist_del it is referring to since
it has been moved under the __unqueue_futex. I can do that as a follow-on though.
> ---
> kernel/futex.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -1288,8 +1288,7 @@ static void mark_wake_futex(struct wake_
> * 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,
>
>
>
--
Darren Hart
VMware Open Source Technology Center
next prev parent reply other threads:[~2017-03-24 21:16 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-22 10:35 [PATCH -v6 00/13] The arduous story of FUTEX_UNLOCK_PI Peter Zijlstra
2017-03-22 10:35 ` [PATCH -v6 01/13] futex: Cleanup variable names for futex_top_waiter() Peter Zijlstra
2017-03-23 18:19 ` [tip:locking/core] " tip-bot for Peter Zijlstra
2017-03-24 21:11 ` [PATCH -v6 01/13] " Darren Hart
2017-03-22 10:35 ` [PATCH -v6 02/13] futex: Use smp_store_release() in mark_wake_futex() Peter Zijlstra
2017-03-23 18:19 ` [tip:locking/core] " tip-bot for Peter Zijlstra
2017-03-24 21:16 ` Darren Hart [this message]
2017-03-22 10:35 ` [PATCH -v6 03/13] futex: Remove rt_mutex_deadlock_account_*() Peter Zijlstra
2017-03-23 18:20 ` [tip:locking/core] " tip-bot for Peter Zijlstra
2017-03-24 21:29 ` [PATCH -v6 03/13] " Darren Hart
2017-03-24 21:31 ` Darren Hart
2017-03-22 10:35 ` [PATCH -v6 04/13] futex,rt_mutex: Provide futex specific rt_mutex API Peter Zijlstra
2017-03-23 18:20 ` [tip:locking/core] " tip-bot for Peter Zijlstra
2017-03-25 0:37 ` [PATCH -v6 04/13] " Darren Hart
2017-04-06 12:15 ` Peter Zijlstra
2017-04-06 17:02 ` Darren Hart
2017-04-05 15:02 ` Darren Hart
2017-04-06 12:17 ` Peter Zijlstra
2017-04-06 17:08 ` Darren Hart
2017-03-22 10:35 ` [PATCH -v6 05/13] futex: Change locking rules Peter Zijlstra
2017-03-23 18:21 ` [tip:locking/core] " tip-bot for Peter Zijlstra
2017-04-05 21:18 ` [PATCH -v6 05/13] " Darren Hart
2017-04-06 12:28 ` Peter Zijlstra
2017-04-06 15:58 ` Joe Perches
2017-04-06 17:21 ` Darren Hart
2017-03-22 10:35 ` [PATCH -v6 06/13] futex: Cleanup refcounting Peter Zijlstra
2017-03-23 18:21 ` [tip:locking/core] " tip-bot for Peter Zijlstra
2017-04-05 21:29 ` [PATCH -v6 06/13] " Darren Hart
2017-03-22 10:35 ` [PATCH -v6 07/13] futex: Rework inconsistent rt_mutex/futex_q state Peter Zijlstra
2017-03-23 18:22 ` [tip:locking/core] " tip-bot for Peter Zijlstra
2017-04-05 21:58 ` [PATCH -v6 07/13] " Darren Hart
2017-03-22 10:35 ` [PATCH -v6 08/13] futex: Pull rt_mutex_futex_unlock() out from under hb->lock Peter Zijlstra
2017-03-23 18:22 ` [tip:locking/core] " tip-bot for Peter Zijlstra
2017-04-05 23:52 ` [PATCH -v6 08/13] " Darren Hart
2017-04-06 12:42 ` Peter Zijlstra
2017-04-06 17:42 ` Darren Hart
2017-03-22 10:35 ` [PATCH -v6 09/13] futex,rt_mutex: Introduce rt_mutex_init_waiter() Peter Zijlstra
2017-03-23 18:23 ` [tip:locking/core] " tip-bot for Peter Zijlstra
2017-04-05 23:57 ` [PATCH -v6 09/13] " Darren Hart
2017-03-22 10:35 ` [PATCH -v6 10/13] futex,rt_mutex: Restructure rt_mutex_finish_proxy_lock() Peter Zijlstra
2017-03-23 18:23 ` [tip:locking/core] " tip-bot for Peter Zijlstra
2017-04-07 23:30 ` [PATCH -v6 10/13] " Darren Hart
2017-04-07 23:35 ` Darren Hart
2017-03-22 10:35 ` [PATCH -v6 11/13] futex: Rework futex_lock_pi() to use rt_mutex_*_proxy_lock() Peter Zijlstra
2017-03-23 18:24 ` [tip:locking/core] " tip-bot for Peter Zijlstra
2017-04-08 0:55 ` [PATCH -v6 11/13] " Darren Hart
2017-04-10 15:51 ` alexander.levin
2017-04-10 16:03 ` Thomas Gleixner
2017-04-14 9:30 ` [tip:locking/core] futex: Avoid freeing an active timer tip-bot for Thomas Gleixner
2017-03-22 10:35 ` [PATCH -v6 12/13] futex: futex_unlock_pi() determinism Peter Zijlstra
2017-03-23 18:24 ` [tip:locking/core] futex: Futex_unlock_pi() determinism tip-bot for Peter Zijlstra
2017-04-08 1:27 ` [PATCH -v6 12/13] futex: futex_unlock_pi() determinism Darren Hart
2017-03-22 10:36 ` [PATCH -v6 13/13] futex: futex_lock_pi() vs PREEMPT_RT_FULL Peter Zijlstra
2017-03-23 18:25 ` [tip:locking/core] futex: Drop hb->lock before enqueueing on the rtmutex tip-bot for Peter Zijlstra
2017-04-08 2:26 ` [PATCH -v6 13/13] futex: futex_lock_pi() vs PREEMPT_RT_FULL Darren Hart
2017-04-08 5:22 ` Mike Galbraith
2017-04-10 8:43 ` Sebastian Andrzej Siewior
2017-04-10 9:08 ` Peter Zijlstra
2017-04-10 16:05 ` Darren Hart
2017-03-24 1:45 ` [PATCH -v6 00/13] The arduous story of FUTEX_UNLOCK_PI Darren Hart
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