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

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Date:   Wed, 13 Apr 2022 21:20:53 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Oleg Nesterov <oleg@...hat.com>
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 Wed, Apr 13, 2022 at 08:59:10PM +0200, Oleg Nesterov wrote:


> +		// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> +		// wrong, needs siglock
> +		current->jobctl &= ~JOBCTL_TRACED_XXX;
> +		wake_up_bit(&current->jobctl, ~JOBCTL_TRACED_XXX_BIT);
		  __wake_up_common_lock()
		    spin_lock_irqsave()
		      current_save_and_set_rtlock_wait_state();

			> +	if (wait_on_bit(&task->jobctl, JOBCTL_TRACED_XXX_BIT, TASK_KILLABLE))
			> +		return -EINTR;
			> +	// now that the tracee cleared JOBCTL_TRACED_XXX_BIT
			> +	// wait_task_inactive() should succeed or fail "really soon".
			> +	if (!wait_task_inactive(child, __TASK_TRACED))
			> +		return ret;


	*whoopsie* ?

>  		preempt_enable_no_resched();
>  		freezable_schedule();
>  		cgroup_leave_frozen(true);