[RFC v4 4/9] namespace: Add umount_end superblock operation

[Joshua Watt <jpewhacker@gmail.com>]

The umount_end operation allows cleaning of state set by umount_begin in
the event the filesystem doesn't actually get unmounted.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
---
 fs/namespace.c     | 22 ++++++++++++++++++++--
 include/linux/fs.h |  1 +
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index d18deb4c410b..d2587be4d08b 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1524,6 +1524,12 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
 	}
 }
 
+static void umount_end(struct super_block *sb, int flags)
+{
+	if (flags & MNT_FORCE && sb->s_op->umount_end)
+		sb->s_op->umount_end(sb);
+}
+
 static void shrink_submounts(struct mount *mnt);
 
 static int do_umount(struct mount *mnt, int flags)
@@ -1589,12 +1595,16 @@ static int do_umount(struct mount *mnt, int flags)
 		 * Special case for "unmounting" root ...
 		 * we just try to remount it readonly.
 		 */
-		if (!capable(CAP_SYS_ADMIN))
-			return -EPERM;
+		if (!capable(CAP_SYS_ADMIN)) {
+			retval = -EPERM;
+			goto out_umount_end;
+		}
 		down_write(&sb->s_umount);
 		if (!sb_rdonly(sb))
 			retval = do_remount_sb(sb, SB_RDONLY, NULL, 0);
 		up_write(&sb->s_umount);
+		/* Still mounted. Always invoke the cleanup */
+		umount_end(sb, flags);
 		return retval;
 	}
 
@@ -1617,6 +1627,14 @@ static int do_umount(struct mount *mnt, int flags)
 	}
 	unlock_mount_hash();
 	namespace_unlock();
+
+out_umount_end:
+	/* If the umount failed and the file system is still mounted, allow the
+	 * driver to cleanup any state it may have setup in umount_begin(). Note
+	 * that this is purposely *not* called when MNT_DETACH is specified.
+	 */
+	if (retval)
+		umount_end(sb, flags);
 	return retval;
 }
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 885266aae2d7..5443c22da18f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1816,6 +1816,7 @@ struct super_operations {
 	int (*statfs) (struct dentry *, struct kstatfs *);
 	int (*remount_fs) (struct super_block *, int *, char *);
 	void (*umount_begin) (struct super_block *);
+	void (*umount_end)(struct super_block *);
 
 	int (*show_options)(struct seq_file *, struct dentry *);
 	int (*show_devname)(struct seq_file *, struct dentry *);
-- 
2.13.6