dm: send empty barriers to targets in dm_flush

Pass empty barrier flushes to the targets in dm_flush().

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index edf9f246769..36142e947ff 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -164,6 +164,9 @@ struct mapped_device {
 
         /* sysfs handle */
         struct kobject kobj;
+
+        /* zero-length barrier that will be cloned and submitted to targets */
+        struct bio barrier_bio;
 };
 
 #define MIN_IOS 256
@@ -1477,6 +1480,13 @@ static int dm_wait_for_completion(struct mapped_device *md, int interruptible)
 static void dm_flush(struct mapped_device *md)
 {
         dm_wait_for_completion(md, TASK_UNINTERRUPTIBLE);
+
+        bio_init(&md->barrier_bio);
+        md->barrier_bio.bi_bdev = md->bdev;
+        md->barrier_bio.bi_rw = WRITE_BARRIER;
+        __split_and_process_bio(md, &md->barrier_bio);
+
+        dm_wait_for_completion(md, TASK_UNINTERRUPTIBLE);
 }
 
 static void process_barrier(struct mapped_device *md, struct bio *bio)