mnt: Delay removal from the mount hash.

- Modify __lookup_mnt_hash_last to ignore mounts that have MNT_UMOUNTED set.
- Don't remove mounts from the mount hash table in propogate_umount
- Don't remove mounts from the mount hash table in umount_tree before
  the entire list of mounts to be umounted is selected.
- Remove mounts from the mount hash table as the last thing that
  happens in the case where a mount has a parent in umount_tree.
  Mounts without parents are not hashed (by definition).

This paves the way for delaying removal from the mount hash table even
farther and fixing the MNT_LOCKED vs MNT_DETACH issue.

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

2 files changed, 8 insertions, 6 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index d1708147eb45..083e3401a808 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -632,14 +632,17 @@ struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
  */
 struct mount *__lookup_mnt_last(struct vfsmount *mnt, struct dentry *dentry)
 {
-        struct mount *p, *res;
-        res = p = __lookup_mnt(mnt, dentry);
+        struct mount *p, *res = NULL;
+        p = __lookup_mnt(mnt, dentry);
         if (!p)
                 goto out;
+        if (!(p->mnt.mnt_flags & MNT_UMOUNT))
+                res = p;
         hlist_for_each_entry_continue(p, mnt_hash) {
                 if (&p->mnt_parent->mnt != mnt || p->mnt_mountpoint != dentry)
                         break;
-                res = p;
+                if (!(p->mnt.mnt_flags & MNT_UMOUNT))
+                        res = p;
         }
 out:
         return res;
@@ -1336,9 +1339,8 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
                 list_move(&p->mnt_list, &tmp_list);
         }
 
-        /* Hide the mounts from lookup_mnt and mnt_mounts */
+        /* Hide the mounts from mnt_mounts */
         list_for_each_entry(p, &tmp_list, mnt_list) {
-                hlist_del_init_rcu(&p->mnt_hash);
                 list_del_init(&p->mnt_child);
         }
 
@@ -1365,6 +1367,7 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
                         p->mnt_mountpoint = p->mnt.mnt_root;
                         p->mnt_parent = p;
                         p->mnt_mp = NULL;
+                        hlist_del_init_rcu(&p->mnt_hash);
                 }
                 change_mnt_propagation(p, MS_PRIVATE);
         }
diff --git a/fs/pnode.c b/fs/pnode.c
index ac3aa0d43b90..c27ae38ee250 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -383,7 +383,6 @@ static void __propagate_umount(struct mount *mnt)
                  */
                 if (child && list_empty(&child->mnt_mounts)) {
                         list_del_init(&child->mnt_child);
-                        hlist_del_init_rcu(&child->mnt_hash);
                         child->mnt.mnt_flags |= MNT_UMOUNT;
                         list_move_tail(&child->mnt_list, &mnt->mnt_list);
                 }