linux-kernel - Re: [PATCH 2/5] sched,ptrace: Fix ptrace_check_attach() vs PREEMPT

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Message-ID: <20220420113547.GA16575@redhat.com>
Date:   Wed, 20 Apr 2022 13:35:48 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     rjw@...ysocki.net, mingo@...nel.org, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, mgorman@...e.de,
        ebiederm@...ssion.com, bigeasy@...utronix.de,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        tj@...nel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH 2/5] sched,ptrace: Fix ptrace_check_attach() vs PREEMPT_RT

On 04/20, Peter Zijlstra wrote:
>
> On Fri, Apr 15, 2022 at 12:57:56PM +0200, Oleg Nesterov wrote:
> >
> > ptrace_resume() does  wake_up_state(child, __TASK_TRACED) but doesn't
> > clear JOBCTL_TRACED. The "else" branch in ptrace_stop() leaks this flag
> > too. Perhaps I missed something, I'll reread 1/5 again, but the main
> > question to me is whether 1-2 actually need the JOBCTL_TRACED_FROZEN flag.
>
> Ok, getting back to this. So I did the change to ptrace_resume(), but
> I'm not entirely sure I understand the issue with the else branch of
> ptrace_stop().
>
> My understanding is that if we hit that else branch, we've raced wth
> __ptrace_unlink(), and that will have done:

Yes, thanks for correcting me, I forgot that may_ptrace_stop() has gone.

Oleg.