From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: 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,
dvhart@infradead.org
Subject: Re: [PATCH -v5 09/14] futex: Rework inconsistent rt_mutex/futex_q state
Date: Tue, 7 Mar 2017 14:26:37 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.20.1703071424250.3584@nanos> (raw)
In-Reply-To: <20170304093559.349677973@infradead.org>
On Sat, 4 Mar 2017, Peter Zijlstra wrote:
> @@ -1402,12 +1402,18 @@ static int wake_futex_pi(u32 __user *uad
> new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
>
> /*
> - * It is possible that the next waiter (the one that brought
> - * top_waiter owner to the kernel) timed out and is no longer
> - * waiting on the lock.
> + * When we interleave with futex_lock_pi() where it does
> + * rt_mutex_timed_futex_lock(), we might observe @this futex_q waiter,
> + * but the rt_mutex's wait_list can be empty (either still, or again,
> + * depending on which side we land).
> + *
> + * When this happens, give up our locks and try again, giving the
> + * futex_lock_pi() instance time to complete and unqueue_me().
time to complete, either by waiting on the rtmutex or removing itself
from the futex queue.
Or something like that.
Thanks,
tglx
next prev parent reply other threads:[~2017-03-07 14:46 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-04 9:27 [PATCH -v5 00/14] the saga of FUTEX_UNLOCK_PI wobbles continues Peter Zijlstra
2017-03-04 9:27 ` [PATCH -v5 01/14] futex: Fix potential use-after-free in FUTEX_REQUEUE_PI Peter Zijlstra
2017-03-14 20:48 ` [tip:locking/urgent] " tip-bot for Peter Zijlstra
2017-03-04 9:27 ` [PATCH -v5 02/14] futex: Add missing error handling to FUTEX_REQUEUE_PI Peter Zijlstra
2017-03-14 20:49 ` [tip:locking/urgent] " tip-bot for Peter Zijlstra
2017-03-04 9:27 ` [PATCH -v5 03/14] futex: Cleanup variable names for futex_top_waiter() Peter Zijlstra
2017-03-04 9:27 ` [PATCH -v5 04/14] futex: Use smp_store_release() in mark_wake_futex() Peter Zijlstra
2017-03-04 9:27 ` [PATCH -v5 05/14] futex: Remove rt_mutex_deadlock_account_*() Peter Zijlstra
2017-03-04 9:27 ` [PATCH -v5 06/14] futex,rt_mutex: Provide futex specific rt_mutex API Peter Zijlstra
2017-03-04 9:27 ` [PATCH -v5 07/14] futex: Change locking rules Peter Zijlstra
2017-03-07 13:22 ` Thomas Gleixner
2017-03-07 16:47 ` Sebastian Andrzej Siewior
2017-03-07 18:01 ` Peter Zijlstra
2017-03-04 9:27 ` [PATCH -v5 08/14] futex: Cleanup refcounting Peter Zijlstra
2017-03-04 9:27 ` [PATCH -v5 09/14] futex: Rework inconsistent rt_mutex/futex_q state Peter Zijlstra
2017-03-07 13:26 ` Thomas Gleixner [this message]
2017-03-04 9:27 ` [PATCH -v5 10/14] futex: Pull rt_mutex_futex_unlock() out from under hb->lock Peter Zijlstra
2017-03-07 14:08 ` Thomas Gleixner
2017-03-07 18:01 ` Peter Zijlstra
2017-03-04 9:27 ` [PATCH -v5 11/14] futex,rt_mutex: Introduce rt_mutex_init_waiter() Peter Zijlstra
2017-03-04 9:27 ` [PATCH -v5 12/14] futex,rt_mutex: Restructure rt_mutex_finish_proxy_lock() Peter Zijlstra
2017-03-07 14:18 ` Thomas Gleixner
2017-03-07 17:57 ` Peter Zijlstra
2017-03-07 17:59 ` Thomas Gleixner
2017-03-08 15:29 ` [PATCH] futex: move debug_rt_mutex_free_waiter() further down Sebastian Andrzej Siewior
2017-03-08 15:37 ` Sebastian Andrzej Siewior
2017-03-08 16:21 ` Steven Rostedt
2017-03-08 16:20 ` Steven Rostedt
2017-03-13 9:16 ` Peter Zijlstra
2017-03-04 9:27 ` [PATCH -v5 13/14] futex: Rework futex_lock_pi() to use rt_mutex_*_proxy_lock() Peter Zijlstra
2017-03-04 9:27 ` [PATCH -v5 14/14] futex: futex_unlock_pi() determinism Peter Zijlstra
2017-03-07 14:31 ` Thomas Gleixner
2017-03-07 17:59 ` Peter Zijlstra
2017-03-13 9:25 ` Peter Zijlstra
2017-03-13 14:25 ` Thomas Gleixner
2017-03-13 15:11 ` Peter Zijlstra
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