switch mnt_hash to hlist

fixes RCU bug - walking through hlist is safe in face of element moves,
since it's self-terminating.  Cyclic lists are not - if we end up jumping
to another hash chain, we'll loop infinitely without ever hitting the
original list head.

[fix for dumb braino folded]

Spotted by: Max Kellermann <mk@cm4all.com>
Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 15 insertions, 11 deletions

diff --git a/fs/pnode.c b/fs/pnode.c
index c7221bb1980..88396df725b 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -220,14 +220,14 @@ static struct mount *get_source(struct mount *dest,
  * @tree_list : list of heads of trees to be attached.
  */
 int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
-		    struct mount *source_mnt, struct list_head *tree_list)
+		    struct mount *source_mnt, struct hlist_head *tree_list)
 {
 	struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
 	struct mount *m, *child;
 	int ret = 0;
 	struct mount *prev_dest_mnt = dest_mnt;
 	struct mount *prev_src_mnt  = source_mnt;
-	LIST_HEAD(tmp_list);
+	HLIST_HEAD(tmp_list);
 
 	for (m = propagation_next(dest_mnt, dest_mnt); m;
 			m = propagation_next(m, dest_mnt)) {
@@ -246,27 +246,29 @@ int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
 		child = copy_tree(source, source->mnt.mnt_root, type);
 		if (IS_ERR(child)) {
 			ret = PTR_ERR(child);
-			list_splice(tree_list, tmp_list.prev);
+			tmp_list = *tree_list;
+			tmp_list.first->pprev = &tmp_list.first;
+			INIT_HLIST_HEAD(tree_list);
 			goto out;
 		}
 
 		if (is_subdir(dest_mp->m_dentry, m->mnt.mnt_root)) {
 			mnt_set_mountpoint(m, dest_mp, child);
-			list_add_tail(&child->mnt_hash, tree_list);
+			hlist_add_head(&child->mnt_hash, tree_list);
 		} else {
 			/*
 			 * This can happen if the parent mount was bind mounted
 			 * on some subdirectory of a shared/slave mount.
 			 */
-			list_add_tail(&child->mnt_hash, &tmp_list);
+			hlist_add_head(&child->mnt_hash, &tmp_list);
 		}
 		prev_dest_mnt = m;
 		prev_src_mnt  = child;
 	}
 out:
 	lock_mount_hash();
-	while (!list_empty(&tmp_list)) {
-		child = list_first_entry(&tmp_list, struct mount, mnt_hash);
+	while (!hlist_empty(&tmp_list)) {
+		child = hlist_entry(tmp_list.first, struct mount, mnt_hash);
 		umount_tree(child, 0);
 	}
 	unlock_mount_hash();
@@ -338,8 +340,10 @@ static void __propagate_umount(struct mount *mnt)
 		 * umount the child only if the child has no
 		 * other children
 		 */
-		if (child && list_empty(&child->mnt_mounts))
-			list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
+		if (child && list_empty(&child->mnt_mounts)) {
+			hlist_del_init_rcu(&child->mnt_hash);
+			hlist_add_before_rcu(&child->mnt_hash, &mnt->mnt_hash);
+		}
 	}
 }
 
@@ -350,11 +354,11 @@ static void __propagate_umount(struct mount *mnt)
  *
  * vfsmount lock must be held for write
  */
-int propagate_umount(struct list_head *list)
+int propagate_umount(struct hlist_head *list)
 {
 	struct mount *mnt;
 
-	list_for_each_entry(mnt, list, mnt_hash)
+	hlist_for_each_entry(mnt, list, mnt_hash)
 		__propagate_umount(mnt);
 	return 0;
 }