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Date: Mon, 4 Nov 2013 19:56:54 -0500
From: Mike Snitzer <snitzer@redhat.com>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: axboe@kernel.dk, kmo@daterainc.com, dm-devel@redhat.com, agk@redhat.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH for-next] dm: fix missing bi_remaining accounting
Message-ID: <20131105005654.GA22356@redhat.com>
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On Mon, Nov 04 2013 at 12:49pm -0500,
Mikulas Patocka <mpatocka@redhat.com> wrote:

> 
> 
> On Mon, 4 Nov 2013, Mike Snitzer wrote:
> 
> > On Mon, Nov 04 2013 at 10:25am -0500,
> > Mikulas Patocka <mpatocka@redhat.com> wrote:
> > 
> > > 
> > > 
> > > On Mon, 4 Nov 2013, Mike Snitzer wrote:
> > > 
> > > > On Mon, Nov 04 2013 at 10:06am -0500,
> > > > Mikulas Patocka <mpatocka@redhat.com> wrote:
> > > > > 
> > > > > The code uses atomic_inc for restoration of bi_remaining. This patch
> > > > > changes it to atomic_set(1) to avoid an interlocked instruction. In the
> > > > > target's bi_endio routine we are sure that bi_remaining is zero
> > > > > (otherwise, the bi_endio routine wouldn't be called) and there are no
> > > > > concurrent users of the bio, so we can replace atomic_inc with
> > > > > atomic_set(1).
> > > > 
> > > > This isn't DM-specific.  Shouldn't the other places in the tree that use
> > > > atomic_inc on bi_remaining should really be converted at the same time?
> > > 
> > > There is no 'atomic_inc.*bi_remaining' in other drivers.
> > 
> > Wrong.  I know btrfs has at least one.  As does bcache afaik.
> 
> grep -r 'atomic_inc.*bi_remaining' * yilds no hits in btrfs or bcache (on 
> git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git , 
> branch remotes/origin/for-next). It only finds 
> drivers/md/dm-cache-target.c, drivers/md/dm-verity.c, 
> drivers/md/dm-snap.c, drivers/md/dm-thin.c. Maybe in other git trees there 
> are more cases of this.

Here is the btrfs one I was thinking of from Chris:
https://patchwork.kernel.org/patch/3123121/

Should probably make its way into linux-block.git, Jens?