vfs: Keep a list of mounts on a mount point

To spot any possible problems call BUG if a mountpoint
is put when it's list of mounts is not empty.

AV: use hlist instead of list_head

Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Eric W. Biederman <ebiederman@twitter.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 8 insertions, 0 deletions

diff --git a/fs/mount.h b/fs/mount.h
index 8c6a2a651254..68bb03ed7f19 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -21,6 +21,7 @@ struct mnt_pcp {
 struct mountpoint {
         struct hlist_node m_hash;
         struct dentry *m_dentry;
+        struct hlist_head m_list;
         int m_count;
 };
 
@@ -51,6 +52,7 @@ struct mount {
         struct mount *mnt_master;       /* slave is on master->mnt_slave_list */
         struct mnt_namespace *mnt_ns;   /* containing namespace */
         struct mountpoint *mnt_mp;      /* where is it mounted */
+        struct hlist_node mnt_mp_list;  /* list mounts with the same mountpoint */
 #ifdef CONFIG_FSNOTIFY
         struct hlist_head mnt_fsnotify_marks;
         __u32 mnt_fsnotify_mask;
diff --git a/fs/namespace.c b/fs/namespace.c
index 77ffdb82f63f..99572dd08336 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -225,6 +225,7 @@ static struct mount *alloc_vfsmnt(const char *name)
                 INIT_LIST_HEAD(&mnt->mnt_share);
                 INIT_LIST_HEAD(&mnt->mnt_slave_list);
                 INIT_LIST_HEAD(&mnt->mnt_slave);
+                INIT_HLIST_NODE(&mnt->mnt_mp_list);
 #ifdef CONFIG_FSNOTIFY
                 INIT_HLIST_HEAD(&mnt->mnt_fsnotify_marks);
 #endif
@@ -731,6 +732,7 @@ static struct mountpoint *new_mountpoint(struct dentry *dentry)
         mp->m_dentry = dentry;
         mp->m_count = 1;
         hlist_add_head(&mp->m_hash, chain);
+        INIT_HLIST_HEAD(&mp->m_list);
         return mp;
 }
 
@@ -738,6 +740,7 @@ static void put_mountpoint(struct mountpoint *mp)
 {
         if (!--mp->m_count) {
                 struct dentry *dentry = mp->m_dentry;
+                BUG_ON(!hlist_empty(&mp->m_list));
                 spin_lock(&dentry->d_lock);
                 dentry->d_flags &= ~DCACHE_MOUNTED;
                 spin_unlock(&dentry->d_lock);
@@ -784,6 +787,7 @@ static void detach_mnt(struct mount *mnt, struct path *old_path)
         mnt->mnt_mountpoint = mnt->mnt.mnt_root;
         list_del_init(&mnt->mnt_child);
         hlist_del_init_rcu(&mnt->mnt_hash);
+        hlist_del_init(&mnt->mnt_mp_list);
         put_mountpoint(mnt->mnt_mp);
         mnt->mnt_mp = NULL;
 }
@@ -800,6 +804,7 @@ void mnt_set_mountpoint(struct mount *mnt,
         child_mnt->mnt_mountpoint = dget(mp->m_dentry);
         child_mnt->mnt_parent = mnt;
         child_mnt->mnt_mp = mp;
+        hlist_add_head(&child_mnt->mnt_mp_list, &mp->m_list);
 }
 
 /*
@@ -1342,6 +1347,7 @@ void umount_tree(struct mount *mnt, int how)
                 if (how < 2)
                         p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
                 if (mnt_has_parent(p)) {
+                        hlist_del_init(&p->mnt_mp_list);
                         put_mountpoint(p->mnt_mp);
                         mnt_add_count(p->mnt_parent, -1);
                         /* move the reference to mountpoint into ->mnt_ex_mountpoint */