md: wait for pending superblock updates before switching to read-only

If a superblock update is pending, wait for it to complete before
letting md_set_readonly() switch to readonly.
Otherwise we might lose important information about a device having
failed.

For external arrays, waiting for superblock updates can wait on
user-space, so in that case, just return an error.

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

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 4f5ecbe94ccb..b8247bc32cf6 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5409,9 +5409,13 @@ static int md_set_readonly(struct mddev *mddev, struct block_device *bdev)
                  * which will now never happen */
                 wake_up_process(mddev->sync_thread->tsk);
 
+        if (mddev->external && test_bit(MD_CHANGE_PENDING, &mddev->flags))
+                return -EBUSY;
         mddev_unlock(mddev);
         wait_event(resync_wait, !test_bit(MD_RECOVERY_RUNNING,
                                           &mddev->recovery));
+        wait_event(mddev->sb_wait,
+                   !test_bit(MD_CHANGE_PENDING, &mddev->flags));
         mddev_lock_nointr(mddev);
 
         mutex_lock(&mddev->open_mutex);