[md PATCH 02/18] md/raid1, raid10: don't recheck "Faulty" flag in read-balance.

NeilBrown
2016-06-02T06:19:52Z

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>
---
drivers/md/raid1.c | 7 -------
drivers/md/raid10.c | 8 --------
2 files changed, 15 deletions(-)

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index c7c8cde0ab21..a54edbe741ff 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -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)
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index c7de2a53e625..cc9e3813e1a4 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -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;