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

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Message-ID: <20220421195551.GO2731@worktop.programming.kicks-ass.net>
Date:   Thu, 21 Apr 2022 21:55:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
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

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.

And I don't see why ptrace_freeze_traced() should fail. It'll warn
though, I should extend/remove that WARN_ON_ONCE() looking at __state,
but it should work.