fix old umount_tree() breakage

Expiry-related code calls umount_tree() several times with
the same list to collect vfsmounts to.  Which is fine, except
that umount_tree() implicitly assumed that the list would
be empty on each call - it moves the victims over there and
then iterates through the list kicking them out.  It's *almost*
idempotent, so everything nearly worked.  However, mnt->ghosts
handling (and thus expirability checks) had been broken - that
part was not idempotent...

The fix is trivial - use local temporary list, splice it to
the the collector list when we are through.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/namespace.c b/fs/namespace.c
index bfcb701..d7fc05f 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1226,15 +1226,16 @@ void release_mounts(struct list_head *head)
  */
 void umount_tree(struct vfsmount *mnt, int propagate, struct list_head *kill)
 {
+       LIST_HEAD(tmp_list);
        struct vfsmount *p;
 
        for (p = mnt; p; p = next_mnt(p, mnt))
-               list_move(&p->mnt_hash, kill);
+               list_move(&p->mnt_hash, &tmp_list);
 
        if (propagate)
-               propagate_umount(kill);
+               propagate_umount(&tmp_list);
 
-       list_for_each_entry(p, kill, mnt_hash) {
+       list_for_each_entry(p, &tmp_list, mnt_hash) {
                list_del_init(&p->mnt_expire);
                list_del_init(&p->mnt_list);
                __touch_mnt_namespace(p->mnt_ns);
@@ -1246,6 +1247,7 @@ void umount_tree(struct vfsmount *mnt, int propagate, struct list_head *kill)
                }
                change_mnt_propagation(p, MS_PRIVATE);
        }
+       list_splice(&tmp_list, kill);
 }
 
 static void shrink_submounts(struct vfsmount *mnt, struct list_head *umounts);