[PATCH] md: Don't remove bitmap from md array when switching to read-only

While a read-only array doesn't not really need a bitmap, we should
not remove the bitmap when switching an array to read-only because
 a/ There is no code to re-add the bitmap which switching to read-write,
 b/ There is insufficient locking - the bitmap could be accessed while it is
    being removed.

Cc: Reuben Farrelly <reuben-lkml@reub.net>
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

drivers/md/md.c

@@ -2689,14 +2689,6 @@ static int do_md_stop(mddev_t * mddev, int ro)
 			set_disk_ro(disk, 1);
 	}
 
-	bitmap_destroy(mddev);
-	if (mddev->bitmap_file) {
-		atomic_set(&mddev->bitmap_file->f_dentry->d_inode->i_writecount, 1);
-		fput(mddev->bitmap_file);
-		mddev->bitmap_file = NULL;
-	}
-	mddev->bitmap_offset = 0;
-
 	/*
 	 * Free resources if final stop
 	 */
@@ -2706,6 +2698,14 @@ static int do_md_stop(mddev_t * mddev, int ro)
 		struct gendisk *disk;
 		printk(KERN_INFO "md: %s stopped.\n", mdname(mddev));
 
+		bitmap_destroy(mddev);
+		if (mddev->bitmap_file) {
+			atomic_set(&mddev->bitmap_file->f_dentry->d_inode->i_writecount, 1);
+			fput(mddev->bitmap_file);
+			mddev->bitmap_file = NULL;
+		}
+		mddev->bitmap_offset = 0;
+
 		ITERATE_RDEV(mddev,rdev,tmp)
 			if (rdev->raid_disk >= 0) {
 				char nm[20];