From: Asias He <asias@redhat.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: Tejun Heo <tj@kernel.org>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V2] block: Avoid missed wakeup in request waitqueue
Date: Wed, 06 Jun 2012 10:14:42 +0800 [thread overview]
Message-ID: <4FCEBD12.4030706@redhat.com> (raw)
In-Reply-To: <20120529012115.GE20954@dhcp-172-17-108-109.mtv.corp.google.com>
Hello, Jens
On 05/29/2012 09:21 AM, Tejun Heo wrote:
> On Tue, May 29, 2012 at 09:15:00AM +0800, Asias He wrote:
>> After hot-unplug a stressed disk, I found that rl->wait[] is not empty
>> while rl->count[] is empty and there are theads still sleeping on
>> get_request after the queue cleanup. With simple debug code, I found
>> there are exactly nr_sleep - nr_wakeup of theads in D state. So there
>> are missed wakeup.
>>
>> $ dmesg | grep nr_sleep
>> [ 52.917115] ---> nr_sleep=1046, nr_wakeup=873, delta=173
>> $ vmstat 1
>> 1 173 0 712640 24292 96172 0 0 0 0 419 757 0 0 0 100 0
>>
>> To quote Tejun:
>>
>> Ah, okay, freed_request() wakes up single waiter with the assumption
>> that after the wakeup there will at least be one successful allocation
>> which in turn will continue the wakeup chain until the wait list is
>> empty - ie. waiter wakeup is dependent on successful request
>> allocation happening after each wakeup. With queue marked dead, any
>> woken up waiter fails the allocation path, so the wakeup chaining is
>> lost and we're left with hung waiters. What we need is wake_up_all()
>> after drain completion.
>>
>> This patch fixes the missed wakeup by waking up all the theads which
>> are sleeping on wait queue after queue drain.
>>
>> Changes in v2: Drop waitqueue_active() optimization
>>
>> Signed-off-by: Asias He<asias@redhat.com>
>
> Acked-by: Tejun Heo<tj@kernel.org>
>
> Jens, this one wants Cc: stable.
Ping.
--
Asias
next prev parent reply other threads:[~2012-06-06 2:13 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-28 4:19 [PATCH] block: Avoid missed wakeup in request waitqueue Asias He
2012-05-28 10:26 ` Tejun Heo
2012-05-29 1:15 ` [PATCH V2] " Asias He
2012-05-29 1:21 ` Tejun Heo
2012-06-06 2:14 ` Asias He [this message]
2012-05-29 1:16 ` [PATCH] " Asias He
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