md/raid5: add rcu protection to rdev accesses in want_replace

Being in the middle of resync is no longer protection against failed
rdevs disappearing.  So add rcu protection.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index e56c7e0627fa..198b2a9eef98 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3239,15 +3239,16 @@ static int want_replace(struct stripe_head *sh, int disk_idx)
 {
         struct md_rdev *rdev;
         int rv = 0;
-        /* Doing recovery so rcu locking not required */
-        rdev = sh->raid_conf->disks[disk_idx].replacement;
+
+        rcu_read_lock();
+        rdev = rcu_dereference(sh->raid_conf->disks[disk_idx].replacement);
         if (rdev
             && !test_bit(Faulty, &rdev->flags)
             && !test_bit(In_sync, &rdev->flags)
             && (rdev->recovery_offset <= sh->sector
                 || rdev->mddev->recovery_cp <= sh->sector))
                 rv = 1;
-
+        rcu_read_unlock();
         return rv;
 }