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    Subject[PATCH 05/11] vfs: Add a function to lazily unmount all mounts from any dentry.

    v2: Always drop the lock when exiting early.
    v3: Make detach_mounts robust about freeing several
    mounts on the same mountpoint at one time, and remove
    the unneeded mnt_list list test.
    v4: Document the purpose of detach_mounts and why new_mountpoint is
    safe to call.

    Signed-off-by: Eric W. Biederman <ebiederman@twitter.com>
    ---
    fs/mount.h | 2 ++
    fs/namespace.c | 39 +++++++++++++++++++++++++++++++++++++++
    2 files changed, 41 insertions(+), 0 deletions(-)

    diff --git a/fs/mount.h b/fs/mount.h
    index 50a72d46e7a6..2b470f34e665 100644
    --- a/fs/mount.h
    +++ b/fs/mount.h
    @@ -84,6 +84,8 @@ extern struct mount *__lookup_mnt_last(struct vfsmount *, struct dentry *);

    extern bool legitimize_mnt(struct vfsmount *, unsigned);

    +extern void detach_mounts(struct dentry *dentry);
    +
    static inline void get_mnt_ns(struct mnt_namespace *ns)
    {
    atomic_inc(&ns->count);
    diff --git a/fs/namespace.c b/fs/namespace.c
    index 33db9e95bd5c..7abbf722ce18 100644
    --- a/fs/namespace.c
    +++ b/fs/namespace.c
    @@ -1359,6 +1359,45 @@ static int do_umount(struct mount *mnt, int flags)
    return retval;
    }

    +/*
    + * detach_mounts - lazily unmount all mounts on the specified dentry
    + *
    + * During unlink, rmdir, and d_drop it is possible to loose the path
    + * to an existing mountpoint, and wind up leaking the mount.
    + * detach_mounts allows lazily unmounting those mounts instead of
    + * leaking them.
    + *
    + * The caller may hold dentry->d_inode->i_mutex.
    + */
    +void detach_mounts(struct dentry *dentry)
    +{
    + struct mountpoint *mp;
    + struct mount *mnt;
    +
    + namespace_lock();
    + if (!d_mountpoint(dentry))
    + goto out_unlock;
    +
    + /*
    + * The namespace lock and d_mountpoint being set guarantees
    + * that new_mountpoint will just be a lookup of the existing
    + * mountpoint structure.
    + */
    + mp = new_mountpoint(dentry);
    + if (IS_ERR(mp))
    + goto out_unlock;
    +
    + lock_mount_hash();
    + while (!list_empty(&mp->m_list)) {
    + mnt = list_first_entry(&mp->m_list, struct mount, mnt_mp_list);
    + umount_tree(mnt, 1);
    + }
    + unlock_mount_hash();
    + put_mountpoint(mp);
    +out_unlock:
    + namespace_unlock();
    +}
    +
    /*
    * Is the caller allowed to modify his namespace?
    */
    --
    1.7.5.4


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