From mboxrd@z Thu Jan  1 00:00:00 1970
From: Oleg Nesterov <oleg@redhat.com>
Date: Wed, 25 May 2022 14:28:46 +0000
Subject: Re: [PATCH 07/16] signal: Wake up the designated parent
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To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: linux-kernel@vger.kernel.org, rjw@rjwysocki.net, mingo@kernel.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de, bigeasy@linutronix.de, Will Deacon <will@kernel.org>, tj@kernel.org, linux-pm@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>, Richard Weinberger <richard@nod.at>, Anton Ivanov <anton.ivanov@cambridgegreys.com>, Johannes Berg <johannes@sipsolutions.net>, linux-um@lists.infradead.org, Chris Zankel <chris@zankel.net>, Max Filippov <jcmvbkbc@gmail.com>, linux-xtensa@linux-xtensa.org, Kees Cook <keescook@chromium.org>, Jann Horn <jannh@google.com>, linux-ia64@vger.kernel.org, Robert OCallahan <roc@pernos.co>, Kyle Huey <khuey@pernos.co>, Richard Henderson <rth@twiddle.net>, Ivan Kokshaysky <ink@jurassic.park.msu.ru>, Matt Turner <mattst88@gmail.com>, Jason Wessel <jason.wessel@windriver.com>, Daniel Thompson <daniel.thompson@linaro.org>, Douglas Anderson <dianders@chromium.org>, Douglas Miller <dougmill@linux.vnet.ibm.com>, Michael Ellerman <mpe@ellerman.id.au>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paulus@samba.org>

On 05/24, Oleg Nesterov wrote:
>
> On 05/24, Oleg Nesterov wrote:
> >
> > I fail to understand this patch...
> >
> > On 05/18, Eric W. Biederman wrote:
> > >
> > > Today if a process is ptraced only the ptracer will ever be woken up in
> > > wait
> >
> > and why is this wrong?
> >
> > > Fixes: 75b95953a569 ("job control: Add @for_ptrace to do_notify_parent_cldstop()")
> >
> > how does this change fix 75b95953a569?
>
> OK, I guess you mean the 2nd do_notify_parent_cldstop() in ptrace_stop(),
> the problematic case is current->ptrace = T. Right?
>
> I dislike this patch anyway, but let me think more about it.

OK, now that I understand the problem, the patch doesn't look bad to me,
although I'd ask to make the changelog more clear.

After this change __wake_up_parent() can't accept any "parent" from
p->parent thread group, but all callers look fine except ptrace_detach().

Oleg.