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

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Message-ID: <20220420180323.GA14947@redhat.com>
Date:   Wed, 20 Apr 2022 20:03:23 +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:
>
> Does something like:
>
> #define JOBCTL_TRACED_BIT		25
> #define JOBCTL_TRACED_QUIESCE_BIT	26
>
> work?

Agreed! ;)

> >  	} else {
> >  		/*
> >  		 * By the time we got the lock, our tracer went away.
> > -		 * Don't drop the lock yet, another tracer may come.
> > -		 *
> > +		 * Don't drop the lock yet, another tracer may come,
> > +		 * tasklist protects us from ptrace_freeze_traced().
> > +		 */
> > +		__set_current_state(TASK_RUNNING);
> > +		clear_traced_xxx();
> > +		/*
> >  		 * If @gstop_done, the ptracer went away between group stop
> >  		 * completion and here.  During detach, it would have set
> >  		 * JOBCTL_STOP_PENDING on us and we'll re-enter
>
> This is that same else clause again; perhaps make signal_wake_up_state()
> also clear TRACED_XXX instead?

I swear, I too thought about this after my last email. Yes, I think this
makes sense. Thanks,

Oleg.