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    SubjectRe: [PATCH 05/11] vfs: Add a function to lazily unmount all mounts from any dentry.
    On Sat, Feb 15, 2014 at 01:37:26PM -0800, Eric W. Biederman wrote:
    >
    > 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);

    Howabout a get_mountpoint(dentry) helper, that returns NULL if it turns out to
    be not a mountpoint? And, as an added bonus, you can drop the comment above as
    well.

    > + 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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