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Commit 4fadd7bb authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Al Viro
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freeze_bdev: kill bd_mount_sem 



Now that we have the freeze count there is not much reason for bd_mount_sem
anymore.  The actual freeze/thaw operations are serialized using the
bd_fsfreeze_mutex, and the only other place we take bd_mount_sem is
get_sb_bdev which tries to prevent mounting a filesystem while the block
device is frozen.  Instead of add a check for bd_fsfreeze_count and
return -EBUSY if a filesystem is frozen.  While that is a change in user
visible behaviour a failing mount is much better for this case rather
than having the mount process stuck uninterruptible for a long time.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 1ba50bbe

fs/block_dev.c

+1 −7
Original line number Diff line number Diff line
@@ -216,8 +216,6 @@ EXPORT_SYMBOL(fsync_bdev); 
 * freeze_bdev  --  lock a filesystem and force it into a consistent state

 * @bdev:	blockdevice to lock

 *

 * 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.

 * The reference counter (bd_fsfreeze_count) guarantees that only the last
@@ -240,7 +238,6 @@ struct super_block *freeze_bdev(struct block_device *bdev) 
	}

	bdev->bd_fsfreeze_count++;



	down(&bdev->bd_mount_sem);

	sb = get_super(bdev);

	if (sb && !(sb->s_flags & MS_RDONLY)) {

		sb->s_frozen = SB_FREEZE_WRITE;
@@ -260,7 +257,6 @@ struct super_block *freeze_bdev(struct block_device *bdev) 
					"VFS:Filesystem freeze failed\n");

				sb->s_frozen = SB_UNFROZEN;

				drop_super(sb);

				up(&bdev->bd_mount_sem);

				bdev->bd_fsfreeze_count--;

				mutex_unlock(&bdev->bd_fsfreeze_mutex);

				return ERR_PTR(error);
@@ -271,7 +267,7 @@ struct super_block *freeze_bdev(struct block_device *bdev) 
	sync_blockdev(bdev);

	mutex_unlock(&bdev->bd_fsfreeze_mutex);



	return sb;	/* thaw_bdev releases s->s_umount and bd_mount_sem */

	return sb;	/* thaw_bdev releases s->s_umount */

}

EXPORT_SYMBOL(freeze_bdev);
@@ -321,7 +317,6 @@ int thaw_bdev(struct block_device *bdev, struct super_block *sb) 
		drop_super(sb);

	}



	up(&bdev->bd_mount_sem);

	mutex_unlock(&bdev->bd_fsfreeze_mutex);

	return 0;

}
@@ -430,7 +425,6 @@ static void init_once(void *foo) 


	memset(bdev, 0, sizeof(*bdev));

	mutex_init(&bdev->bd_mutex);

	sema_init(&bdev->bd_mount_sem, 1);

	INIT_LIST_HEAD(&bdev->bd_inodes);

	INIT_LIST_HEAD(&bdev->bd_list);

#ifdef CONFIG_SYSFS

fs/super.c

+7 −2
Original line number Diff line number Diff line
@@ -743,9 +743,14 @@ int get_sb_bdev(struct file_system_type *fs_type, 
	 * will protect the lockfs code from trying to start a snapshot

	 * while we are mounting

	 */

	down(&bdev->bd_mount_sem);

	mutex_lock(&bdev->bd_fsfreeze_mutex);

	if (bdev->bd_fsfreeze_count > 0) {

		mutex_unlock(&bdev->bd_fsfreeze_mutex);

		error = -EBUSY;

		goto error_bdev;

	}

	s = sget(fs_type, test_bdev_super, set_bdev_super, bdev);

	up(&bdev->bd_mount_sem);

	mutex_unlock(&bdev->bd_fsfreeze_mutex);

	if (IS_ERR(s))

		goto error_s;

include/linux/fs.h

+0 −1
Original line number Diff line number Diff line
@@ -640,7 +640,6 @@ struct block_device { 
	struct super_block *	bd_super;

	int			bd_openers;

	struct mutex		bd_mutex;	/* open/close mutex */

	struct semaphore	bd_mount_sem;

	struct list_head	bd_inodes;

	void *			bd_holder;

	int			bd_holders;