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

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Date:   Mon, 18 Apr 2022 19:19:42 +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 04/18, Oleg Nesterov wrote:
>
>  static int ptrace_check_attach(struct task_struct *child, bool ignore_state)
>  {
...
> +	if (!traced)
> +		return -ESRCH;
> +
> +	WARN_ON(READ_ONCE(child->__state) == __TASK_TRACED);
> +	if (ignore_state)
> +		return 0;
> +
> +	if (!task_is_traced(child))
> +		return -ESRCH;

This is the new check V1 didn't have, we need it to unsure that check_attach
can't miss the change in child->jobctl and call wait_task_inactive() before
the child marks itself as "traced" and clears JOBCTL_TRACED_XXX.

Oleg.