md: fix uninitialized use of mddev->recovery_wait

If an array was created with --assume-clean we will oops when trying to
set ->resync_max.

Fix this by initializing ->recovery_wait in mddev_find.

Cc: <stable@kernel.org>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/md/md.c

@@ -276,6 +276,7 @@ static mddev_t * mddev_find(dev_t unit)
 	atomic_set(&new->active, 1);
 	spin_lock_init(&new->write_lock);
 	init_waitqueue_head(&new->sb_wait);
+	init_waitqueue_head(&new->recovery_wait);
 	new->reshape_position = MaxSector;
 	new->resync_max = MaxSector;
 	new->level = LEVEL_NONE;
@@ -5665,7 +5666,6 @@ void md_do_sync(mddev_t *mddev)
 		window/2,(unsigned long long) max_sectors/2);
 
 	atomic_set(&mddev->recovery_active, 0);
-	init_waitqueue_head(&mddev->recovery_wait);
 	last_check = 0;
 
 	if (j>2) {