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SubjectRe: [RFC][PATCH 1/3] vfs: Keep a list of mounts on a mount point
On Fri, Oct 04, 2013 at 03:42:37PM -0700, Eric W. Biederman wrote:
>
> Signed-off-by: Eric W. Biederman <ebiederman@twitter.com>
> ---
> fs/mount.h | 2 ++
> fs/namespace.c | 5 +++++
> 2 files changed, 7 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..d092964fe7f9 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;
> }
>
> @@ -691,6 +693,7 @@ static void detach_mnt(struct mount *mnt, struct path *old_path)
> list_del_init(&mnt->mnt_hash);
> put_mountpoint(mnt->mnt_mp);
> mnt->mnt_mp = NULL;
> + list_del_init(&mnt->mnt_mp_list);

Should be done *before* put_mountpoint(), for obvious reasons.

And a BUG_ON(!list_empty(&mp->m_list)) in put_mountpoint() for good measure (and
no, WARN_ON() is not better here, since use-after-free is definitely worse than
a BUG).

> }
>
> /*
> @@ -705,6 +708,7 @@ 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);
> }
>
> /*
> @@ -1193,6 +1197,7 @@ void umount_tree(struct mount *mnt, int propagate)
> p->mnt_parent->mnt_ghosts++;
> put_mountpoint(p->mnt_mp);
> p->mnt_mp = NULL;
> + list_del_init(&mnt->mnt_mp_list);

Ditto.

> }
> change_mnt_propagation(p, MS_PRIVATE);
> }
> --
> 1.7.5.4
>


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