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Date:   Tue, 7 Jun 2022 17:26:54 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     linux-kernel@vger.kernel.org, rjw@rjwysocki.net, mingo@kernel.org,
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        Paul Mackerras <paulus@samba.org>
Subject: Re: [PATCH 07/16] signal: Wake up the designated parent
Message-ID: <20220607152627.GA10192@redhat.com>
References: <871qwq5ucx.fsf_-_@email.froward.int.ebiederm.org>
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On 06/06, Eric W. Biederman wrote:
>
> Which if I have had enough sleep reduces this patch to just:
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index f072959fcab7..c8156366b722 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -1431,8 +1431,10 @@ static int child_wait_callback(wait_queue_entry_t *wait, unsigned mode,
>         if (!eligible_pid(wo, p))
>                 return 0;
>
> -       if ((wo->wo_flags & __WNOTHREAD) && wait->private != p->parent)
> -               return 0;
> +       if ((wo->wo_flags & __WNOTHREAD) &&
> +           (wait->private != p->parent) &&
> +           (wait->private != p->real_parent))
> +                       return 0;
>
>         return default_wake_function(wait, mode, sync, key);
>  }
>
>
> I think that solves the issue without missing wake-ups without adding
> any more.

Agreed, and looks much simpler.

> For the same set of reasons it looks like the __wake_up_parent in
> __ptrace_detach is just simply dead code.  I don't think there is a case
> where when !ptrace_reparented the thread that is the real_parent can
> sleep in do_wait when the thread that was calling ptrace could not.

Yes... this doesn't really differ from the case when one thread reaps
a natural child and another thread sleep in do_wait().

> That needs a very close look to confirm.

Yes.

Oleg.