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Date:   Tue, 10 May 2022 17:34:53 +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>,
        linux-xtensa@linux-xtensa.org, Kees Cook <keescook@chromium.org>,
        Jann Horn <jannh@google.com>, linux-ia64@vger.kernel.org
Subject: Re: [PATCH v4 10/12] ptrace: Don't change __state
Message-ID: <20220510153452.GA23707@redhat.com>
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 <20220510142202.GB23277@redhat.com>
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On 05/10, Eric W. Biederman wrote:
>
> > But I still think that a lockless
> >
> > 	if (!(task->jobctl & JOBCTL_PTRACE_FROZEN))
> > 		return;
> >
> > check at the start of ptrace_unfreeze_traced() makes sense to avoid
> > lock_task_sighand() if possible.
> >
> > And ptrace_resume() can probably clear JOBCTL_PTRACE_FROZEN along with
> > JOBCTL_TRACED to make this optimization work better. The same for
> > ptrace_signal_wake_up().
>
> What do you have that suggests that taking siglock there is a problem?

Not necessarily a problem, but this optimization is free. If the tracee
was resumed, it can compete for siglock with debugger.

> What you propose will definitely work as an incremental change, and
> in an incremental change we can explain why doing the stupid simple
> thing is not good enough.

OK.

Oleg.