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

[FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>]

On Mon, 28 Jun 2010 10:18:48 +0200
Jens Axboe <axboe@kernel.dk> wrote:

> 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.

Probably, that's would be fine (we need to fix memory leak in that
path). I guess that requeue with the partial completion commands might
cause problems.