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Re: [dm-devel] [PATCH 1/2] block: fix leaks associated with discard request payload



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


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