linux-kernel - Re: [PATCH] virtio_blk: fix race between start and stop queue

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CACVXFVP8ZT-eSHMmHnZ2Trx63HW+X2qtekpkLW35NWGXWsJ0GQ@mail.gmail.com>
Date:	Fri, 16 May 2014 23:15:34 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH] virtio_blk: fix race between start and stop queue

On Fri, May 16, 2014 at 10:57 PM, Jens Axboe <axboe@...nel.dk> wrote:
> On 2014-05-16 08:53, Jens Axboe wrote:
>>
>> On 2014-05-15 06:33, Ming Lei wrote:
>>>
>>> When there isn't enough vring descriptor for adding to vq,
>>> blk-mq will be put as stopped state until some of pending
>>> descriptors are completed & freed.
>>>
>>> Unfortunately, the vq's interrupt may come just before
>>> blk-mq's BLK_MQ_S_STOPPED flag is set, so the blk-mq will
>>> still be kept as stopped even though lots of descriptors
>>> are completed and freed in the interrupt handler. The worst
>>> case is that all pending descriptors are freed in the
>>> interrupt handler, and the queue is kept as stopped forever.
>>>
>>> This patch fixes the problem by starting/stopping blk-mq
>>> with holding vq_lock.
>>
>>
>> Why not just use blk_mq_start_hw_queues()?
>
>
> Or, if you want to maintain current heuristics, just move the start and stop
> under the vq_lock. That should prevent the race, as far as I can tell. Not
> sure what that extra queue_stopped would buy you, seems a lot cleaner to
> just maintain this state exclusively in the queue.

Yes.

But the flag can avoid to call blk_mq_start_stopped_hw_queues()
unnecessarily, which needn't at most of times.  Considered that
the interrupt may happen with very high frequency, I suggest to
introduce the extra flag.


Thanks,
-- 
Ming Lei
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/