linux-kernel - Re: [RFC][PATCH 2/2] exec: If possible don't wait for ptraced threads to be reaped

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Date:   Mon, 03 Apr 2017 16:04:58 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Aleksa Sarai <asarai@...e.com>,
        Andy Lutomirski <luto@...capital.net>,
        Attila Fazekas <afazekas@...hat.com>,
        Jann Horn <jann@...jh.net>, Kees Cook <keescook@...omium.org>,
        Michal Hocko <mhocko@...nel.org>,
        Ulrich Obergfell <uobergfe@...hat.com>,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [RFC][PATCH 2/2] exec: If possible don't wait for ptraced threads to be reaped

Oleg Nesterov <oleg@...hat.com> writes:

> On 04/02, Eric W. Biederman wrote:
>>
>> Oleg Nesterov <oleg@...hat.com> writes:
>>
>> > And btw zap_other_threads(may_hang == 0) is racy. Either you need tasklist or
>> > exit_notify() should set tsk->exit_state under siglock, otherwise zap() can
>> > return the wrong count.
>>
>> zap_other_thread(tsk, 0) only gets called in the case where we don't
>> care about the return value.  It does not get called from fs/exec.c
>
> I meant that may_hang == 0 implies zap_other_threads(do_count => -1) which should
> return the number of threads which didn't pass exit_notify(). The returned value
> can be wrong unless you change exit_notify() to set exit_state under
> siglock.

Interesting an existing bug.  I won't deny that one.

Subtle to catch but easy enough to fix.

Eric