[PATCH] md: Improve detection of lack of barrier support in raid1
Move the test for 'do barrier work' down a bit so that if the first write to a
raid1 is a BIO_RW_BARRIER write, the checking done by superblock writes will
cause the right thing to happen.
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 532d040..b8c13c8 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -753,18 +753,24 @@
const int rw = bio_data_dir(bio);
int do_barriers;
- if (unlikely(!mddev->barriers_work && bio_barrier(bio))) {
- bio_endio(bio, bio->bi_size, -EOPNOTSUPP);
- return 0;
- }
-
/*
* Register the new request and wait if the reconstruction
* thread has put up a bar for new requests.
* Continue immediately if no resync is active currently.
+ * We test barriers_work *after* md_write_start as md_write_start
+ * may cause the first superblock write, and that will check out
+ * if barriers work.
*/
+
md_write_start(mddev, bio); /* wait on superblock update early */
+ if (unlikely(!mddev->barriers_work && bio_barrier(bio))) {
+ if (rw == WRITE)
+ md_write_end(mddev);
+ bio_endio(bio, bio->bi_size, -EOPNOTSUPP);
+ return 0;
+ }
+
wait_barrier(conf);
disk_stat_inc(mddev->gendisk, ios[rw]);