md/raid10: fix deadlock with unaligned read during resync
If the 'bio_split' path in raid10-read is used while
resync/recovery is happening it is possible to deadlock.
Fix this be elevating ->nr_waiting for the duration of both
parts of the split request.
This fixes a bug that has been present since 2.6.22
but has only started manifesting recently for unknown reasons.
It is suitable for and -stable since then.
Reported-by: Justin Bronder <jsbronder@gentoo.org>
Tested-by: Justin Bronder <jsbronder@gentoo.org>
Signed-off-by: NeilBrown <neilb@suse.de>
Cc: stable@kernel.org
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 42e64e4..d1d6891 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -825,11 +825,29 @@
*/
bp = bio_split(bio,
chunk_sects - (bio->bi_sector & (chunk_sects - 1)) );
+
+ /* Each of these 'make_request' calls will call 'wait_barrier'.
+ * If the first succeeds but the second blocks due to the resync
+ * thread raising the barrier, we will deadlock because the
+ * IO to the underlying device will be queued in generic_make_request
+ * and will never complete, so will never reduce nr_pending.
+ * So increment nr_waiting here so no new raise_barriers will
+ * succeed, and so the second wait_barrier cannot block.
+ */
+ spin_lock_irq(&conf->resync_lock);
+ conf->nr_waiting++;
+ spin_unlock_irq(&conf->resync_lock);
+
if (make_request(mddev, &bp->bio1))
generic_make_request(&bp->bio1);
if (make_request(mddev, &bp->bio2))
generic_make_request(&bp->bio2);
+ spin_lock_irq(&conf->resync_lock);
+ conf->nr_waiting--;
+ wake_up(&conf->wait_barrier);
+ spin_unlock_irq(&conf->resync_lock);
+
bio_pair_release(bp);
return 0;
bad_map: