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Date:   Tue, 26 Apr 2022 20:11:42 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Peter Zijlstra <peterz@infradead.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>,
        linux-kernel@vger.kernel.org, tj@kernel.org,
        linux-pm@vger.kernel.org
Subject: Re: [PATCH v2 2/5] sched,ptrace: Fix ptrace_check_attach() vs
 PREEMPT_RT
Message-ID: <20220426181141.GA13647@redhat.com>
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On 04/26, Eric W. Biederman wrote:
>
> Relying on __ptrace_unlink assumes the __ptrace_unlink happens after
> siglock is taken before calling ptrace_stop.  Especially with the
> ptrace_notify in signal_delivered that does not look guaranteed.
>
> The __ptrace_unlink could also happen during arch_ptrace_stop.
>
> Relying on siglock is sufficient because __ptrace_unlink holds siglock
> over clearing task->ptrace.  Which means that the simple fix for this is
> to just test task->ptrace before we set JOBCTL_TRACED_QUEIESCE.

Or simply clear _QUEIESCE along with _TRACED/DELAY_WAKEKILL before return?

Oleg.