Re: [PATCH for-next] dm: fix missing bi_remaining accounting

From: Mikulas Patocka
Date: Mon Nov 04 2013 - 12:49:25 EST




On Mon, 4 Nov 2013, Mike Snitzer wrote:

> On Mon, Nov 04 2013 at 10:25am -0500,
> Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
>
> >
> >
> > On Mon, 4 Nov 2013, Mike Snitzer wrote:
> >
> > > On Mon, Nov 04 2013 at 10:06am -0500,
> > > Mikulas Patocka <mpatocka@xxxxxxxxxx> 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.

Mikulas
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