linux-kernel - Re: [PATCH] pid: Add a judgment for ns null in pid_nr

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Message-ID: <20250819142557.GA11345@redhat.com>
Date: Tue, 19 Aug 2025 16:25:58 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Christian Brauner <brauner@...nel.org>
Cc: Xiang Gao <gxxa03070307@...il.com>, joel.granados@...nel.org,
	lorenzo.stoakes@...cle.com, linux-kernel@...r.kernel.org,
	gaoxiang17 <gaoxiang17@...omi.com>, mjguzik@...il.com,
	Liam.Howlett@...cle.com, viro@...iv.linux.org.uk
Subject: Re: [PATCH] pid: Add a judgment for ns null in pid_nr_ns

On 08/19, Christian Brauner wrote:
>
> On Sat, 02 Aug 2025 10:21:23 +0800, Xiang Gao wrote:
> > __task_pid_nr_ns
> >         ns = task_active_pid_ns(current);
> >         pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
> >                 if (pid && ns->level <= pid->level) {
> >
> > Sometimes null is returned for task_active_pid_ns. Then it will trigger kernel panic in pid_nr_ns.
> >
> > [...]
>
> Applied to the vfs-6.18.pidfs branch of the vfs/vfs.git tree.
> Patches in the vfs-6.18.pidfs branch should appear in linux-next soon.
>
> Please report any outstanding bugs that were missed during review in a
> new review to the original patch series allowing us to drop it.
>
> It's encouraged to provide Acked-bys and Reviewed-bys even though the
> patch has now been applied. If possible patch trailers will be updated.
>
> Note that commit hashes shown below are subject to change due to rebase,
> trailer updates or similar. If in doubt, please check the listed branch.
>
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
> branch: vfs-6.18.pidfs
>
> [1/1] pid: Add a judgment for ns null in pid_nr_ns
>       https://git.kernel.org/vfs/vfs/c/006568ab4c5c
> [1/4] pid: make __task_pid_nr_ns(ns => NULL) safe for zombie callers
>       https://git.kernel.org/vfs/vfs/c/abdfd4948e45
> [3/4] pid: change bacct_add_tsk() to use task_ppid_nr_ns()
>       https://git.kernel.org/vfs/vfs/c/b1afcaddd6c8
> [4/4] pid: change task_state() to use task_ppid_nr_ns()
>       https://git.kernel.org/vfs/vfs/c/d00f5232851c

Hmm. The 1st patch adds the ns != NULL check into pid_nr_ns().

This means that "[1/4] pid: make __task_pid_nr_ns(ns => NULL) safe for zombie callers"
(commit  abdfd4948e45c51b19 in vfs-6.18.pidfs) is not needed.

OTOH... You didn't take

	[PATCH 2/4] pid: introduce task_ppid_vnr()
	https://lore.kernel.org/all/20250810173610.GA19995@redhat.com/

currently in -mm tree. It is purely cosmetic, but imo makes sense.

Oleg.