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Date:   Wed, 27 Apr 2022 16:43:00 +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,
        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>,
        inux-xtensa@linux-xtensa.org, Kees Cook <keescook@chromium.org>,
        Jann Horn <jannh@google.com>
Subject: Re: [PATCH 6/9] signal: Always call do_notify_parent_cldstop with
 siglock held
Message-ID: <20220427144259.GB17421@redhat.com>
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On 04/27, Eric W. Biederman wrote:
>
> The ptrace parental relationship definitely has the potential to be a
> graph with cycles.  Which as you point out is not fine.
>
> The result is very nice and I don't want to give it up.  I suspect
> something ptrace cycles are always a problem and can simply be
> forbidden.

OK, please consider another case.

We have a parent P and its child C. C traces P.

This is not that unusual, I don't think we can forbid this case.

P reports an event and calls do_notify_parent_cldstop().

C receives SIGSTOP and calls do_notify_parent_cldstop() too.

Oleg.