block: fix non-atomic access to genhd inflight structures

After the stack plugging introduction, these are called lockless.
Ensure that the counters are updated atomically.

Signed-off-by: Shaohua Li<shaohua.li@intel.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 88820704a191..0cf68b478878 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -477,7 +477,8 @@ static void start_io_acct(struct dm_io *io)
         cpu = part_stat_lock();
         part_round_stats(cpu, &dm_disk(md)->part0);
         part_stat_unlock();
-        dm_disk(md)->part0.in_flight[rw] = atomic_inc_return(&md->pending[rw]);
+        atomic_set(&dm_disk(md)->part0.in_flight[rw],
+                atomic_inc_return(&md->pending[rw]));
 }
 
 static void end_io_acct(struct dm_io *io)
@@ -497,8 +498,8 @@ static void end_io_acct(struct dm_io *io)
          * After this is decremented the bio must not be touched if it is
          * a flush.
          */
-        dm_disk(md)->part0.in_flight[rw] = pending =
-                atomic_dec_return(&md->pending[rw]);
+        pending = atomic_dec_return(&md->pending[rw]);
+        atomic_set(&dm_disk(md)->part0.in_flight[rw], pending);
         pending += atomic_read(&md->pending[rw^0x1]);
 
         /* nudge anyone waiting on suspend queue */