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Commit 414e6b9a authored by NeilBrown's avatar NeilBrown Committed by Shaohua Li
Browse files

md/raid1, raid10: don't recheck "Faulty" flag in read-balance. 



Re-checking the faulty flag here brings no value.
The comment about "risk" refers to the risk that the device could
be in the process of being removed by ->hot_remove_disk().
However providing that the ->nr_pending count is incremented inside
an rcu_read_locked() region, there is no risk of that happening.

This is because the rdev pointer (in the personalities array) is set
to NULL before synchronize_rcu(), and ->nr_pending is tested
afterwards.  If the rcu_read_locked region happens before the
synchronize_rcu(), the test will see that nr_pending has been incremented.
If it happens afterwards, the rdev pointer will be NULL so there is nothing
to increment.

Signed-off-by: default avatarNeilBrown <neilb@suse.com>
Signed-off-by: default avatarShaohua Li <shli@fb.com>
parent 8430e7e0

drivers/md/raid1.c

+0 −7
Original line number Diff line number Diff line
@@ -689,13 +689,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect 
		if (!rdev)

			goto retry;

		atomic_inc(&rdev->nr_pending);

		if (test_bit(Faulty, &rdev->flags)) {

			/* cannot risk returning a device that failed

			 * before we inc'ed nr_pending

			 */

			rdev_dec_pending(rdev, conf->mddev);

			goto retry;

		}

		sectors = best_good_sectors;



		if (conf->mirrors[best_disk].next_seq_sect != this_sector)

drivers/md/raid10.c

+0 −8
Original line number Diff line number Diff line
@@ -707,7 +707,6 @@ static struct md_rdev *read_balance(struct r10conf *conf, 


	raid10_find_phys(conf, r10_bio);

	rcu_read_lock();

retry:

	sectors = r10_bio->sectors;

	best_slot = -1;

	best_rdev = NULL;
@@ -804,13 +803,6 @@ static struct md_rdev *read_balance(struct r10conf *conf, 


	if (slot >= 0) {

		atomic_inc(&rdev->nr_pending);

		if (test_bit(Faulty, &rdev->flags)) {

			/* Cannot risk returning a device that failed

			 * before we inc'ed nr_pending

			 */

			rdev_dec_pending(rdev, conf->mddev);

			goto retry;

		}

		r10_bio->read_slot = slot;

	} else

		rdev = NULL;