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

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

On Mon, 28 Jun 2010 17:25:36 +0200
Christoph Hellwig <hch lst de> wrote:

> On Mon, Jun 28, 2010 at 05:14:28PM +0900, FUJITA Tomonori wrote:
> > > 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?
> 
> Actually the SSDs don't fully hang, they just causes lots of I/O errors
> and hit the error handler hard.  The hard hang is when running under
> qemu.  Apply the patch below, then create an if=scsi drive that resides
> on an XFS filesystem, and you'll have scsi TP support in the guest:

Ok, I figured out what's wrong.

As I suspected, it's due to the partial completion.

qemu scsi driver tells that the WRITE_SAME command was successful but
somehow the command has resid. So we retry it again and again (and
leak some memory).

I don't know yet why qemu scsi driver is broken. Maybe there is a bug
in it or converting discard to FS sends broken commands to the driver.

I'll try to figure out it tomorrow.

I've put a patch to complete discard command in the all-or-nothing
manner:

git://git.kernel.org/pub/scm/linux/kernel/git/tomo/linux-2.6-misc.git discard


At least, the guest kernel doesn't hang for me.