vfs: keep list of mounts for each superblock

Keep track of vfsmounts belonging to a superblock.  List is protected
by vfsmount_lock.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Tested-by: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/mount.h

@@ -29,6 +29,7 @@ struct mount {
 #endif
 	struct list_head mnt_mounts;	/* list of children, anchored here */
 	struct list_head mnt_child;	/* and going through their mnt_child */
+	struct list_head mnt_instance;	/* mount instance on sb->s_mounts */
 	const char *mnt_devname;	/* Name of device e.g. /dev/dsk/hda1 */
 	struct list_head mnt_list;
 	struct list_head mnt_expire;	/* link in fs-specific expiry list */

fs/namespace.c

@@ -671,6 +671,9 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void
 	mnt->mnt.mnt_sb = root->d_sb;
 	mnt->mnt_mountpoint = mnt->mnt.mnt_root;
 	mnt->mnt_parent = mnt;
+	br_write_lock(vfsmount_lock);
+	list_add_tail(&mnt->mnt_instance, &root->d_sb->s_mounts);
+	br_write_unlock(vfsmount_lock);
 	return &mnt->mnt;
 }
 EXPORT_SYMBOL_GPL(vfs_kern_mount);
@@ -699,6 +702,9 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root,
 		mnt->mnt.mnt_root = dget(root);
 		mnt->mnt_mountpoint = mnt->mnt.mnt_root;
 		mnt->mnt_parent = mnt;
+		br_write_lock(vfsmount_lock);
+		list_add_tail(&mnt->mnt_instance, &sb->s_mounts);
+		br_write_unlock(vfsmount_lock);
 
 		if (flag & CL_SLAVE) {
 			list_add(&mnt->mnt_slave, &old->mnt_slave_list);
@@ -781,6 +787,7 @@ static void mntput_no_expire(struct mount *mnt)
 		acct_auto_close_mnt(&mnt->mnt);
 		goto put_again;
 	}
+	list_del(&mnt->mnt_instance);
 	br_write_unlock(vfsmount_lock);
 	mntfree(mnt);
 }

fs/super.c

@@ -142,6 +142,7 @@ static struct super_block *alloc_super(struct file_system_type *type)
 		INIT_LIST_HEAD(&s->s_dentry_lru);
 		INIT_LIST_HEAD(&s->s_inode_lru);
 		spin_lock_init(&s->s_inode_lru_lock);
+		INIT_LIST_HEAD(&s->s_mounts);
 		init_rwsem(&s->s_umount);
 		mutex_init(&s->s_lock);
 		lockdep_set_class(&s->s_umount, &type->s_umount_key);
@@ -200,6 +201,7 @@ static inline void destroy_super(struct super_block *s)
 	free_percpu(s->s_files);
 #endif
 	security_sb_free(s);
+	WARN_ON(!list_empty(&s->s_mounts));
 	kfree(s->s_subtype);
 	kfree(s->s_options);
 	kfree(s);

include/linux/fs.h

@@ -1428,6 +1428,7 @@ struct super_block {
 #else
 	struct list_head	s_files;
 #endif
+	struct list_head	s_mounts;	/* list of mounts; _not_ for fs use */
 	/* s_dentry_lru, s_nr_dentry_unused protected by dcache.c lru locks */
 	struct list_head	s_dentry_lru;	/* unused dentry lru */
 	int			s_nr_dentry_unused;	/* # of dentry on lru */