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>

diff --git a/fs/mount.h b/fs/mount.h
index 8c6a2a6..68bb03e 100644 (file)
--- 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 77ffdb8..99572dd 100644 (file)
--- 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 */