Commit 51e9ac77 authored by NeilBrown's avatar NeilBrown
Browse files

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: default avatarJustin Bronder <jsbronder@gentoo.org>
Tested-by: default avatarJustin Bronder <jsbronder@gentoo.org>
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
Cc: stable@kernel.org
parent 69e51b44

drivers/md/raid10.c

+18 −0
Original line number Original line Diff line number Diff line
@@ -825,11 +825,29 @@ static int make_request(mddev_t *mddev, struct bio * bio) 
		 */

		 */

		bp = bio_split(bio,

		bp = bio_split(bio,

			       chunk_sects - (bio->bi_sector & (chunk_sects - 1)) );

			       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))

		if (make_request(mddev, &bp->bio1))

			generic_make_request(&bp->bio1);

			generic_make_request(&bp->bio1);

		if (make_request(mddev, &bp->bio2))

		if (make_request(mddev, &bp->bio2))

			generic_make_request(&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);

		bio_pair_release(bp);

		return 0;

		return 0;

	bad_map:

	bad_map:

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