[PATCH] Revert bd_mount_mutex back to a semaphore

Revert bd_mount_mutex back to a semaphore so that xfs_freeze -f /mnt/newtest;
xfs_freeze -u /mnt/newtest works safely and doesn't produce lockdep warnings.

(XFS unlocks the semaphore from a different task, by design. The mutex
code warns about this)

Signed-off-by: Dave Chinner <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/block_dev.c

···
 	{
 		memset(bdev, 0, sizeof(*bdev));
 		mutex_init(&bdev->bd_mutex);
-		mutex_init(&bdev->bd_mount_mutex);
+		sema_init(&bdev->bd_mount_sem, 1);
 		INIT_LIST_HEAD(&bdev->bd_inodes);
 		INIT_LIST_HEAD(&bdev->bd_list);
 #ifdef CONFIG_SYSFS

fs/buffer.c

···
  * freeze_bdev  --  lock a filesystem and force it into a consistent state
  * @bdev:	blockdevice to lock
  *
- * This takes the block device bd_mount_mutex to make sure no new mounts
+ * This takes the block device bd_mount_sem to make sure no new mounts
  * happen on bdev until thaw_bdev() is called.
  * If a superblock is found on this device, we take the s_umount semaphore
  * on it to make sure nobody unmounts until the snapshot creation is done.
···
 {
 	struct super_block *sb;
 
-	mutex_lock(&bdev->bd_mount_mutex);
+	down(&bdev->bd_mount_sem);
 	sb = get_super(bdev);
 	if (sb && !(sb->s_flags & MS_RDONLY)) {
 		sb->s_frozen = SB_FREEZE_WRITE;
···
 		drop_super(sb);
 	}
 
-	mutex_unlock(&bdev->bd_mount_mutex);
+	up(&bdev->bd_mount_sem);
 }
 EXPORT_SYMBOL(thaw_bdev);
 

fs/gfs2/ops_fstype.c

···
 		error = -EBUSY;
 		goto error;
 	}
-	mutex_lock(&sb->s_bdev->bd_mount_mutex);
+	down(&sb->s_bdev->bd_mount_sem);
 	new = sget(fs_type, test_bdev_super, set_bdev_super, sb->s_bdev);
-	mutex_unlock(&sb->s_bdev->bd_mount_mutex);
+	up(&sb->s_bdev->bd_mount_sem);
 	if (IS_ERR(new)) {
 		error = PTR_ERR(new);
 		goto error;

fs/super.c

···
 	 * will protect the lockfs code from trying to start a snapshot
 	 * while we are mounting
 	 */
-	mutex_lock(&bdev->bd_mount_mutex);
+	down(&bdev->bd_mount_sem);
 	s = sget(fs_type, test_bdev_super, set_bdev_super, bdev);
-	mutex_unlock(&bdev->bd_mount_mutex);
+	up(&bdev->bd_mount_sem);
 	if (IS_ERR(s))
 		goto error_s;
 

include/linux/fs.h

···
 	struct inode *		bd_inode;	/* will die */
 	int			bd_openers;
 	struct mutex		bd_mutex;	/* open/close mutex */
-	struct mutex		bd_mount_mutex;	/* mount mutex */
+	struct semaphore	bd_mount_sem;
 	struct list_head	bd_inodes;
 	void *			bd_holder;
 	int			bd_holders;