Re: [PATCH] pid: Add a judgment for ns null in pid_nr_ns

[Oleg Nesterov <oleg@redhat.com>]

ping...

We need either

  [1/1] pid: Add a judgment for ns null in pid_nr_ns
  https://git.kernel.org/vfs/vfs/c/006568ab4c5c

or

  [1/4] pid: make __task_pid_nr_ns(ns => NULL) safe for zombie callers
  https://git.kernel.org/vfs/vfs/c/abdfd4948e45

in any case imo the changelog should explain why do we care
to check ns != NUll, "Sometimes null is returned for task_active_pid_ns"
doesn't look like a good explanation...

Oleg.

On 08/19, Oleg Nesterov wrote:
>
> 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.