dm-verity: fix prefetch-vs-suspend race

There's a possible race condition in dm-verity - the prefetch work item
may race with suspend and it is possible that prefetch continues to run
while the device is suspended. Fix this by calling flush_workqueue and
dm_bufio_client_reset in the postsuspend hook.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org

Author: Mikulas Patocka

drivers/md/dm-verity-target.c

@@ -836,6 +836,13 @@ static int verity_map(struct dm_target *ti, struct bio *bio)
 	return DM_MAPIO_SUBMITTED;
 }
 
+static void verity_postsuspend(struct dm_target *ti)
+{
+	struct dm_verity *v = ti->private;
+	flush_workqueue(v->verify_wq);
+	dm_bufio_client_reset(v->bufio);
+}
+
 /*
  * Status: V (valid) or C (corruption found)
  */
@@ -1806,6 +1813,7 @@ static struct target_type verity_target = {
 	.ctr		= verity_ctr,
 	.dtr		= verity_dtr,
 	.map		= verity_map,
+	.postsuspend	= verity_postsuspend,
 	.status		= verity_status,
 	.prepare_ioctl	= verity_prepare_ioctl,
 	.iterate_devices = verity_iterate_devices,