Re: [PATCH 1/2] block: fix leaks associated with discard requestpayload

From: FUJITA Tomonori
Date: Mon Jun 28 2010 - 04:15:20 EST

On Mon, 28 Jun 2010 09:57:38 +0200
Christoph Hellwig <hch@xxxxxx> 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@xxxxxx> 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.

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

Any way to reproduce the hang without ssd drives?
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