Quoting Eric W. Biederman (ebied...@xmission.com):
>
> To spot any possible problems call BUG if a mountpoint
> is put when it's list of mounts is not empty.
>
> Signed-off-by: Eric W. Biederman <ebieder...@twitter.com>
Acked-by: Serge Hallyn <serge.hal...@canonical.com>
> ---
> fs/mount.h | 2 ++
> fs/namespace.c | 6 ++++++
> 2 files changed, 8 insertions(+), 0 deletions(-)
>
> diff --git a/fs/mount.h b/fs/mount.h
> index 64a858143ff9..e4342b8dfab1 100644
> --- a/fs/mount.h
> +++ b/fs/mount.h
> @@ -21,6 +21,7 @@ struct mnt_pcp {
> struct mountpoint {
> struct list_head m_hash;
> struct dentry *m_dentry;
> + struct list_head m_list;
> int m_count;
> };
>
> @@ -47,6 +48,7 @@ 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 list_head 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 da5c49483430..e4fe22c23e00 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -197,6 +197,7 @@ 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_LIST_HEAD(&mnt->mnt_mp_list);
> #ifdef CONFIG_FSNOTIFY
> INIT_HLIST_HEAD(&mnt->mnt_fsnotify_marks);
> #endif
> @@ -636,6 +637,7 @@ static struct mountpoint *new_mountpoint(struct dentry
> *dentry)
> mp->m_dentry = dentry;
> mp->m_count = 1;
> list_add(&mp->m_hash, chain);
> + INIT_LIST_HEAD(&mp->m_list);
> return mp;
> }
>
> @@ -643,6 +645,7 @@ static void put_mountpoint(struct mountpoint *mp)
> {
> if (!--mp->m_count) {
> struct dentry *dentry = mp->m_dentry;
> + BUG_ON(!list_empty(&mp->m_list));
> spin_lock(&dentry->d_lock);
> dentry->d_flags &= ~DCACHE_MOUNTED;
> spin_unlock(&dentry->d_lock);
> @@ -689,6 +692,7 @@ static void detach_mnt(struct mount *mnt, struct path
> *old_path)
> mnt->mnt_mountpoint = mnt->mnt.mnt_root;
> list_del_init(&mnt->mnt_child);
> list_del_init(&mnt->mnt_hash);
> + list_del_init(&mnt->mnt_mp_list);
> put_mountpoint(mnt->mnt_mp);
> mnt->mnt_mp = NULL;
> }
> @@ -705,6 +709,7 @@ 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;
> + list_add_tail(&child_mnt->mnt_mp_list, &mp->m_list);
> }
>
> /*
> @@ -1191,6 +1196,7 @@ void umount_tree(struct mount *mnt, int propagate)
> list_del_init(&p->mnt_child);
> if (mnt_has_parent(p)) {
> p->mnt_parent->mnt_ghosts++;
> + list_del_init(&p->mnt_mp_list);
> put_mountpoint(p->mnt_mp);
> p->mnt_mp = NULL;
> }
> --
> 1.7.5.4
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