linux-kernel - Re: [PATCH v2 5/5] freezer,sched: Rewrite core freezer logic

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Date:   Fri, 22 Apr 2022 10:52:01 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     rjw@...ysocki.net, oleg@...hat.com, mingo@...nel.org,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, mgorman@...e.de, bigeasy@...utronix.de,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        tj@...nel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 5/5] freezer,sched: Rewrite core freezer logic

Peter Zijlstra <peterz@...radead.org> writes:

> On Thu, Apr 21, 2022 at 09:55:51PM +0200, Peter Zijlstra wrote:
>> On Thu, Apr 21, 2022 at 12:26:44PM -0500, Eric W. Biederman wrote:
>> > Peter Zijlstra <peterz@...radead.org> writes:
>> > 
>> > > --- a/kernel/ptrace.c
>> > > +++ b/kernel/ptrace.c
>> > > @@ -288,7 +288,7 @@ static int ptrace_check_attach(struct ta
>> > >  	}
>> > >  	__set_current_state(TASK_RUNNING);
>> > >  
>> > > -	if (!wait_task_inactive(child, TASK_TRACED) ||
>> > > +	if (!wait_task_inactive(child, TASK_TRACED|TASK_FREEZABLE) ||
>> > >  	    !ptrace_freeze_traced(child))
>> > >  		return -ESRCH;
>> > 
>> > Do we mind that this is going to fail if the child is frozen
>> > during ptrace_check_attach?
>> 
>> Why should this fail? wait_task_inactive() will in fact succeed if it is
>> frozen due to the added TASK_FREEZABLE and some wait_task_inactive()
>> changes elsewhere in this patch.
>
> These:

I had missed that change to wait_task_inactive.

Still that change to wait_task_inactive fundamentally depends upon the
fact that we don't care about the state we are passing into
wait_task_inactive.  So I think it would be better to simply have a
precursor patch that changes wait_task_inactive(child, TASK_TRACED) to
wait_task_inactive(child, 0) and say so explicitly.

Eric