releases/4.4.140/dm-bufio-don-t-take-the-lock-in-dm_bufio_shrink_count.patch

   1 From d12067f428c037b4575aaeb2be00847fc214c24a Mon Sep 17 00:00:00 2001
   2 From: Mikulas Patocka <mpatocka@redhat.com>
   3 Date: Wed, 23 Nov 2016 16:52:01 -0500
   4 Subject: dm bufio: don't take the lock in dm_bufio_shrink_count
   5
   6 From: Mikulas Patocka <mpatocka@redhat.com>
   7
   8 commit d12067f428c037b4575aaeb2be00847fc214c24a upstream.
   9
  10 dm_bufio_shrink_count() is called from do_shrink_slab to find out how many
  11 freeable objects are there. The reported value doesn't have to be precise,
  12 so we don't need to take the dm-bufio lock.
  13
  14 Suggested-by: David Rientjes <rientjes@google.com>
  15 Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
  16 Signed-off-by: Mike Snitzer <snitzer@redhat.com>
  17 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  18
  19 ---
  20  drivers/md/dm-bufio.c |   16 ++++------------
  21  1 file changed, 4 insertions(+), 12 deletions(-)
  22
  23 --- a/drivers/md/dm-bufio.c
  24 +++ b/drivers/md/dm-bufio.c
  25 @@ -1574,19 +1574,11 @@ dm_bufio_shrink_scan(struct shrinker *sh
  26  static unsigned long
  27  dm_bufio_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
  28  {
  29 -       struct dm_bufio_client *c;
  30 -       unsigned long count;
  31 -       unsigned long retain_target;
  32 +       struct dm_bufio_client *c = container_of(shrink, struct dm_bufio_client, shrinker);
  33 +       unsigned long count = READ_ONCE(c->n_buffers[LIST_CLEAN]) +
  34 +                             READ_ONCE(c->n_buffers[LIST_DIRTY]);
  35 +       unsigned long retain_target = get_retain_buffers(c);
  36
  37 -       c = container_of(shrink, struct dm_bufio_client, shrinker);
  38 -       if (sc->gfp_mask & __GFP_FS)
  39 -               dm_bufio_lock(c);
  40 -       else if (!dm_bufio_trylock(c))
  41 -               return 0;
  42 -
  43 -       count = c->n_buffers[LIST_CLEAN] + c->n_buffers[LIST_DIRTY];
  44 -       retain_target = get_retain_buffers(c);
  45 -       dm_bufio_unlock(c);
  46         return (count < retain_target) ? 0 : (count - retain_target);
  47  }
  48