On Mon, Aug 25, 2025 at 05:43:18AM +0100, Al Viro wrote:
> ... and document that locking requirements for is_path_reachable().
> There is one questionable caller in do_listmount() where we are not
> holding mount_lock *and* might not have the first argument mounted.
> However, in that case it will immediately return true without having
> to look at the ancestors. Might be cleaner to move the check into
> non-LSTM_ROOT case which it really belongs in - there the check is
> not always true and is_mounted() is guaranteed.
>
> Document the locking environments for is_path_reachable() callers:
> get_peer_under_root()
> get_dominating_id()
> do_statmount()
> do_listmount()
>
> Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> ---
Reviewed-by: Christian Brauner <brauner@xxxxxxxxxx>
> fs/namespace.c | 12 ++++++------
> fs/pnode.c | 3 ++-
> 2 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/fs/namespace.c b/fs/namespace.c
> index acacfe767a7c..bf9a3a644faa 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -4592,7 +4592,7 @@ SYSCALL_DEFINE5(move_mount,
> /*
> * Return true if path is reachable from root
> *
> - * namespace_sem or mount_lock is held
> + * locks: mount_locked_reader || namespace_shared && is_mounted(mnt)
> */
> bool is_path_reachable(struct mount *mnt, struct dentry *dentry,
> const struct path *root)
> @@ -4606,11 +4606,9 @@ bool is_path_reachable(struct mount *mnt, struct dentry *dentry,
>
> bool path_is_under(const struct path *path1, const struct path *path2)
> {
> - bool res;
> - read_seqlock_excl(&mount_lock);
> - res = is_path_reachable(real_mount(path1->mnt), path1->dentry, path2);
> - read_sequnlock_excl(&mount_lock);
> - return res;
> + scoped_guard(mount_locked_reader)
> + return is_path_reachable(real_mount(path1->mnt), path1->dentry,
> + path2);
Same thing, no need for this scoped guard eyesore.
