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>

4 files changed, 11 insertions, 0 deletions

diff --git a/fs/mount.h b/fs/mount.h
index 0921b51e27e2..4ef36d93e5a2 100644
--- a/fs/mount.h
+++ b/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 */
diff --git a/fs/namespace.c b/fs/namespace.c
index db65e2e4921f..145217b088d1 100644
--- a/fs/namespace.c
+++ b/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 @@ put_again:
                 acct_auto_close_mnt(&mnt->mnt);
                 goto put_again;
         }
+        list_del(&mnt->mnt_instance);
         br_write_unlock(vfsmount_lock);
         mntfree(mnt);
 }
diff --git a/fs/super.c b/fs/super.c
index 0413f51a9f0f..993ca8f128d6 100644
--- a/fs/super.c
+++ b/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);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index cc1021fd19ef..03385acd71e8 100644
--- a/include/linux/fs.h
+++ b/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 */