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

[Christoph Hellwig <hch lst de>]

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