that's the condition we are actually trying to check there...
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
fs/namespace.c | 62 +++++++++++---------------------------------------
1 file changed, 13 insertions(+), 49 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index b229f74762de..e783eb801060 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2329,67 +2329,31 @@ struct vfsmount *collect_mounts(const struct path *path)
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();
--
2.39.5
