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

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Message-ID: <878rrys5yj.fsf@email.froward.int.ebiederm.org>
Date:   Thu, 21 Apr 2022 12:26:44 -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:

> --- 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?

I think to avoid that we need to safely get this to
wait_task_inactive(child, 0), like the coredump code uses.

I would like to say that we can do without the wait_task_inactive,
but it looks like it is necessary to ensure that all of the userspace
registers are saved where the tracer can get at them.

Eric