mnt: In umount_tree reuse mnt_list instead of mnt_hash

umount_tree builds a list of mounts that need to be unmounted.
Utilize mnt_list for this purpose instead of mnt_hash.  This begins to
allow keeping a mount on the mnt_hash after it is unmounted, which is
necessary for a properly functioning MNT_LOCKED implementation.

The fact that mnt_list is an ordinary list makding available list_move
is nice bonus.

Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 11 insertions, 9 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index c68d9fc912e7..54cbef129f4a 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1327,23 +1327,25 @@ enum umount_tree_flags {
  */
 static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
 {
-        HLIST_HEAD(tmp_list);
+        LIST_HEAD(tmp_list);
         struct mount *p;
 
-        for (p = mnt; p; p = next_mnt(p, mnt)) {
-                hlist_del_init_rcu(&p->mnt_hash);
-                hlist_add_head(&p->mnt_hash, &tmp_list);
-        }
+        /* Gather the mounts to umount */
+        for (p = mnt; p; p = next_mnt(p, mnt))
+                list_move(&p->mnt_list, &tmp_list);
 
-        hlist_for_each_entry(p, &tmp_list, mnt_hash)
+        /* Hide the mounts from lookup_mnt and mnt_mounts */
+        list_for_each_entry(p, &tmp_list, mnt_list) {
+                hlist_del_init_rcu(&p->mnt_hash);
                 list_del_init(&p->mnt_child);
+        }
 
+        /* Add propogated mounts to the tmp_list */
         if (how & UMOUNT_PROPAGATE)
                 propagate_umount(&tmp_list);
 
-        while (!hlist_empty(&tmp_list)) {
-                p = hlist_entry(tmp_list.first, struct mount, mnt_hash);
-                hlist_del_init_rcu(&p->mnt_hash);
+        while (!list_empty(&tmp_list)) {
+                p = list_first_entry(&tmp_list, struct mount, mnt_list);
                 list_del_init(&p->mnt_expire);
                 list_del_init(&p->mnt_list);
                 __touch_mnt_namespace(p->mnt_ns);