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dissolve_on_fput(): use anon_ns_root()

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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>
This commit is contained in:
Al Viro
2025-06-08 23:41:23 -04:00
parent 05da054d43
commit 9ed4b9eaea
1 changed files with 14 additions and 50 deletions
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64
fs/namespace.c
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@@ -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) {
if (!anon_ns_root(m))
return;
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))
return;
lock_mount_hash();
umount_tree(m, UMOUNT_CONNECTED);
unlock_mount_hash();