md: move GET_BITMAP_FILE ioctl out from mddev_lock.
It makes more sense to report bitmap_info->file, rather than
bitmap->file (the later is only available once the array is
active).
With that change, use mddev->lock to protect bitmap_info being
set to NULL, and we can call get_bitmap_file() without taking
the mutex.
Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 8770308..b4fbd6a 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -393,6 +393,7 @@
* in_sync - and related safemode and MD_CHANGE changes
* pers (also protected by reconfig_mutex and pending IO).
* clearing ->bitmap
+ * clearing ->bitmap_info.file
*/
spinlock_t lock;
wait_queue_head_t sb_wait; /* for waiting on superblock updates */