md: move bitmap_destroy to the beginning of __md_stop

Since we have switched to sync way to handle METADATA_UPDATED
msg for md-cluster, then process_metadata_update is depended
on mddev->thread->wqueue.

With the new change, clustered raid could possible hang if
array received a METADATA_UPDATED msg after array unregistered
mddev->thread, so we need to stop clustered raid (bitmap_destroy
-> bitmap_free -> md_cluster_stop) earlier than unregister
thread (mddev_detach -> md_unregister_thread).

And this change should be safe for non-clustered raid since
all writes are stopped before the destroy. Also in md_run,
we activate the personality (pers->run()) before activating
the bitmap (bitmap_create()). So it is pleasingly symmetric
to stop the bitmap (bitmap_destroy()) before stopping the
personality (__md_stop() calls pers->free()), we achieve this
by move bitmap_destroy to the beginning of __md_stop.

But we don't want to break the codes for waiting behind IO as
Shaohua mentioned, so introduce bitmap_wait_behind_writes to
call the codes, and call the new fun in both mddev_detach and
bitmap_destroy, then we will not break original behind IO code
and also fit the new condition well.

Signed-off-by: Guoqing Jiang <gqjiang@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/md/bitmap.h b/drivers/md/bitmap.h
index 9f761097aab2..d15721ac07a6 100644
--- a/drivers/md/bitmap.h
+++ b/drivers/md/bitmap.h
@@ -271,6 +271,7 @@ struct bitmap *get_bitmap_from_slot(struct mddev *mddev, int slot);
 int bitmap_copy_from_slot(struct mddev *mddev, int slot,
 				sector_t *lo, sector_t *hi, bool clear_bits);
 void bitmap_free(struct bitmap *bitmap);
+void bitmap_wait_behind_writes(struct mddev *mddev);
 #endif
 
 #endif