From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>, Al Viro <viro@ZenIV.linux.org.uk>,
Bart Van Assche <bvanassche@acm.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Neil Brown <neilb@suse.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] sched/wait: avoid abort_exclusive_wait() in __wait_on_bit_lock()
Date: Fri, 2 Sep 2016 00:17:43 +0200 [thread overview]
Message-ID: <20160901221743.GJ10168@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20160901190141.GJ10138@twins.programming.kicks-ass.net>
On Thu, Sep 01, 2016 at 09:01:41PM +0200, Peter Zijlstra wrote:
> On Fri, Aug 26, 2016 at 02:45:52PM +0200, Oleg Nesterov wrote:
>
> > We do not need anything tricky to avoid the race,
>
> The race being:
>
> CPU0 CPU1 CPU2
>
> __wait_on_bit_lock()
> bit_wait_io()
> io_schedule()
>
> clear_bit_unlock()
> __wake_up_common(.nr_exclusive=1)
> list_for_each_entry()
> if (curr->func() && --nr_exclusive)
> break
>
> signal()
>
> if (signal_pending_state()) == TRUE
> return -EINTR
>
> And no progress because CPU1 exits without acquiring the lock and CPU0
> thinks its done because it woke someone.
FWIW, the way the mutex code avoids this issue is by doing the
signal_pending test while holding the q->lock, that way its exclusive
with wakeup.
next prev parent reply other threads:[~2016-09-01 22:17 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-26 12:44 [PATCH 0/2] sched/wait: abort_exclusive_wait() should pass TASK_NORMAL to wake_up() Oleg Nesterov
2016-08-26 12:45 ` [PATCH 1/2] " Oleg Nesterov
2016-09-01 11:39 ` Peter Zijlstra
2016-09-01 17:26 ` Oleg Nesterov
2016-09-01 18:09 ` Peter Zijlstra
2016-08-26 12:45 ` [PATCH 2/2] sched/wait: avoid abort_exclusive_wait() in __wait_on_bit_lock() Oleg Nesterov
2016-08-26 12:47 ` Oleg Nesterov
2016-09-01 19:01 ` Peter Zijlstra
2016-09-01 19:08 ` Peter Zijlstra
2016-09-02 12:06 ` Oleg Nesterov
2016-09-01 22:17 ` Peter Zijlstra [this message]
2016-09-02 12:06 ` Oleg Nesterov
2016-09-02 13:20 ` Peter Zijlstra
2016-09-02 12:06 ` Oleg Nesterov
2016-09-01 11:03 ` [PATCH 0/2] sched/wait: abort_exclusive_wait() should pass TASK_NORMAL to wake_up() Peter Zijlstra
[not found] <00e501d201cf$7bfecd40$73fc67c0$@alibaba-inc.com>
2016-08-29 8:41 ` [PATCH 2/2] sched/wait: avoid abort_exclusive_wait() in __wait_on_bit_lock() Hillf Danton
2016-08-29 13:48 ` Oleg Nesterov
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