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    Subject[PATCH 04/12] 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.

    Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>
    Signed-off-by: Eric W. Biederman <ebiederman@twitter.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 18511835dc28..5375da0dc570 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;
    };

    @@ -48,6 +49,7 @@ 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 abe2f56efaea..32d380eabdac 100644
    --- a/fs/namespace.c
    +++ b/fs/namespace.c
    @@ -195,6 +195,7 @@ 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
    @@ -695,6 +696,7 @@ 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;
    }

    @@ -702,6 +704,7 @@ 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);
    @@ -748,6 +751,7 @@ 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;
    }
    @@ -764,6 +768,7 @@ 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);
    }

    /*
    @@ -1246,6 +1251,7 @@ void umount_tree(struct mount *mnt, int how)
    p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
    list_del_init(&p->mnt_child);
    if (mnt_has_parent(p)) {
    + list_del_init(&p->mnt_mp_list);
    put_mountpoint(p->mnt_mp);
    /* move the reference to mountpoint into ->mnt_ex_mountpoint */
    p->mnt_ex_mountpoint.dentry = p->mnt_mountpoint;
    --
    1.7.5.4

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