Re: [PATCH 2/4] pid_ns: (BUG 11391) change ->child_reaper when init->group_leader exits

[Oleg Nesterov <oleg@tv-sign.ru>]

On 08/26, sukadev@us.ibm.com wrote:
>
> sukadev@us.ibm.com [sukadev@us.ibm.com] wrote:
> | I was able to repro the problem without the patchset and could  not
> | reproduce  with the patchset. But just had a quick question while
> | reviewing the patches.
> |
> | Oleg Nesterov [oleg@tv-sign.ru] wrote:
> | | We don't change pid_ns->child_reaper when the main thread of the
> | | subnamespace init exits. As Robert Rex <robert.rex@exasol.com>
> | | pointed out this is wrong.
> | |
> | | Yes, the re-parenting itself works correctly, but if the reparented
> | | task exits it needs ->parent->nsproxy->pid_ns in do_notify_parent(),
> |
> | If the task was reparented, then with patch 1/4 its parent would be
> | the global init (init_pid_ns.child_reaper) right ?
> |
> | | and if the main thread is zombie its ->nsproxy was already cleared
> | | by exit_task_namespaces().
> |
> | If above is true, then even if the main thread's nsproxy is NULL, does
> | it affect the reparented task ?
>
> never mind. I see it now. The group_dead check in current code is not
> sufficient (and the zap_pid_ns() may not have been called when main
> thread is exiting).

Yes.

BTW, your original patch (which introduced zap_pid_ns()) was correct ;)
The code was broken later, during the s/->pid/vpid/ conversion.

The group_dead check _is_ sufficient (and correct) for zap_pid_ns(),
but we all missed the simple fact: if we continue to re-parent to
some task, it must have the valid ->nsproxy->pid_ns. Thanks to Robert
again.

Oleg.