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

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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>
This commit is contained in:
NeilBrown 2016-06-02 16:19:52 +10:00 committed by Shaohua Li
parent 8430e7e0af
commit 414e6b9a70
2 changed files with 0 additions and 15 deletions
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7
drivers/md/raid1.c
View File

@ -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)

8
drivers/md/raid10.c
View File

@ -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;