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

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Message-ID: <20100628075738.GA26606@lst.de>
Date:	Mon, 28 Jun 2010 09:57:38 +0200
From:	Christoph Hellwig <hch@....de>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	hch@....de, snitzer@...hat.com, axboe@...nel.dk,
	dm-devel@...hat.com, James.Bottomley@...e.de,
	linux-kernel@...r.kernel.org, martin.petersen@...cle.com,
	akpm@...ux-foundation.org, linux-scsi@...r.kernel.org
Subject: Re: [PATCH 1/2] block: fix leaks associated with discard request payload

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@....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.
While I see the problems with leaking ressources in that case I still
can't quite explain the hang I see.

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