Message-ID: <4C285AE8.9090702@kernel.dk>
Date: Mon, 28 Jun 2010 10:18:48 +0200
From: Jens Axboe <axboe@kernel.dk>
MIME-Version: 1.0
To: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
CC: hch@lst.de, snitzer@redhat.com, dm-devel@redhat.com,
       James.Bottomley@suse.de, linux-kernel@vger.kernel.org,
       martin.petersen@oracle.com, akpm@linux-foundation.org,
       linux-scsi@vger.kernel.org
Subject: Re: [PATCH 1/2] block: fix leaks associated with discard request
  payload
References: <20100627110712.GA14511@lst.de>	<20100627212952D.fujita.tomonori@lab.ntt.co.jp>	<20100628075738.GA26606@lst.de> <20100628171218Q.fujita.tomonori@lab.ntt.co.jp>
In-Reply-To: <20100628171218Q.fujita.tomonori@lab.ntt.co.jp>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1509
Lines: 39

On 2010-06-28 10:14, FUJITA Tomonori wrote:
> On Mon, 28 Jun 2010 09:57:38 +0200
> Christoph Hellwig <hch@lst.de> wrote:
> 
>> On Sun, Jun 27, 2010 at 09:32:07PM +0900, FUJITA Tomonori wrote:
>>> On Sun, 27 Jun 2010 13:07:12 +0200
>>> Christoph Hellwig <hch@lst.de> wrote:
>>>
>>>>> How about this?
>>>>
>>>> As I tried to explain before this utterly confuses the I/O completion
>>>> path.  With the patch applied even a simple mkfs.xfs that issues discard
>>>> just hangs.
>>>
>>> Wired. I just tried mkfs.xfs against scsi_debug with my block patches
>>> (I saw one discard command). Seemed that it worked fine.
>>
>> I've tracked it down to the call to scsi_requeue_command in scsi_end_request.
>> When the command is marked BLOCK_PC we'll just get it back as such in
>> ->prep_fn next time, but now it's reverting to the previous state.
> 
> If scsi_end_request() calls scsi_requeue_command(), the command has a
> left over (i.e. hasn't finished all the data), right? You hit such
> condition with discard commands?
> 
> BLOCK_PC requests don't hit this case since blk_end_request() always
> return false for PC.

You can get requeues on the ->queuecommand() path as well, for a
variety of reasons, and that would be what Christoph is hitting.

-- 
Jens Axboe

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