dissolve_on_fput(): use anon_ns_root()

that's the condition we are actually trying to check there...

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/namespace.c b/fs/namespace.c
index ea01fea2ac93ca5dd4a25831c337b4515589bad5..151d5f3360b932494bbbf431260ac028a4165ef1 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2333,67 +2333,31 @@ void drop_collected_paths(struct path *paths, struct path *prealloc)
 static void free_mnt_ns(struct mnt_namespace *);
 static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *, bool);
 
-static inline bool must_dissolve(struct mnt_namespace *mnt_ns)
-{
-       /*
-        * This mount belonged to an anonymous mount namespace
-        * but was moved to a non-anonymous mount namespace and
-        * then unmounted.
-        */
-       if (unlikely(!mnt_ns))
-               return false;
-
-       /*
-        * This mount belongs to a non-anonymous mount namespace
-        * and we know that such a mount can never transition to
-        * an anonymous mount namespace again.
-        */
-       if (!is_anon_ns(mnt_ns)) {
-               /*
-                * A detached mount either belongs to an anonymous mount
-                * namespace or a non-anonymous mount namespace. It
-                * should never belong to something purely internal.
-                */
-               VFS_WARN_ON_ONCE(mnt_ns == MNT_NS_INTERNAL);
-               return false;
-       }
-
-       return true;
-}
-
 void dissolve_on_fput(struct vfsmount *mnt)
 {
        struct mnt_namespace *ns;
        struct mount *m = real_mount(mnt);
 
+       /*
+        * m used to be the root of anon namespace; if it still is one,
+        * we need to dissolve the mount tree and free that namespace.
+        * Let's try to avoid taking namespace_sem if we can determine
+        * that there's nothing to do without it - rcu_read_lock() is
+        * enough to make anon_ns_root() memory-safe and once m has
+        * left its namespace, it's no longer our concern, since it will
+        * never become a root of anon ns again.
+        */
+
        scoped_guard(rcu) {
-               if (!must_dissolve(READ_ONCE(m->mnt_ns)))
+               if (!anon_ns_root(m))
                        return;
        }
 
        scoped_guard(namespace_lock, &namespace_sem) {
-               ns = m->mnt_ns;
-               if (!must_dissolve(ns))
-                       return;
-
-               /*
-                * After must_dissolve() we know that this is a detached
-                * mount in an anonymous mount namespace.
-                *
-                * Now when mnt_has_parent() reports that this mount
-                * tree has a parent, we know that this anonymous mount
-                * tree has been moved to another anonymous mount
-                * namespace.
-                *
-                * So when closing this file we cannot unmount the mount
-                * tree. This will be done when the file referring to
-                * the root of the anonymous mount namespace will be
-                * closed (It could already be closed but it would sync
-                * on @namespace_sem and wait for us to finish.).
-                */
-               if (mnt_has_parent(m))
+               if (!anon_ns_root(m))
                        return;
 
+               ns = m->mnt_ns;
                lock_mount_hash();
                umount_tree(m, UMOUNT_CONNECTED);
                unlock_mount_hash();