md: don't clear MD_CHANGE_CLEAN in md_update_sb() for external arrays

If this bit is cleared in md_update_sb() the kernel will allow writes to the
array if userspace triggers md_allow_write(), e.g. through stripe_cache_size,
when mdmon is not active.  When mdmon is active the array transitions to
active-idle bypassing write-pending, setting up a race for mdmon to set the
array clean before a write arrives.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index c148b6302154..a1f6b59b8b37 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2167,9 +2167,10 @@ repeat:
                                 rdev->recovery_offset = mddev->curr_resync_completed;
 
         }       
-        if (mddev->external || !mddev->persistent) {
+        if (!mddev->persistent) {
+                if (!mddev->external)
+                        clear_bit(MD_CHANGE_CLEAN, &mddev->flags);
                 clear_bit(MD_CHANGE_DEVS, &mddev->flags);
-                clear_bit(MD_CHANGE_CLEAN, &mddev->flags);
                 wake_up(&mddev->sb_wait);
                 return;
         }