md/raid1, raid10: don't recheck "Faulty" flag in read-balance. (414e6b9a) · Commits · 戴 / test

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:

NeilBrown <neilb@suse.com> Signed-off-by:

Shaohua Li <shli@fb.com>

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 @@ retry:

		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;

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