linux-kernel - Re: [PATCH next] sched,freezer: prevent tasks from escaping being frozen

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Message-ID: <20250708072852.GD1613376@noisy.programming.kicks-ass.net>
Date: Tue, 8 Jul 2025 09:28:52 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Chen Ridong <chenridong@...weicloud.com>
Cc: timvp@...gle.com, Michal Koutn?? <mkoutny@...e.com>, rafael@...nel.org,
	pavel@...nel.org, tj@...nel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, lujialin4@...wei.com,
	chenridong@...wei.com
Subject: Re: [PATCH next] sched,freezer: prevent tasks from escaping being
 frozen

On Mon, Jul 07, 2025 at 07:32:59PM +0800, Chen Ridong wrote:

> Below is the race condition scenario:
> 
> get_signal				read freezer.state
> try_to_freeze
> __refrigerator				freezer_read
> 					update_if_frozen
> WRITE_ONCE(current->__state, TASK_FROZEN);			
> 					// The task is set to frozen(now, frozen(task) == ture).
> 					// we suppose other tasks are all frozen.
> 					// set cgroup frozen when all tasks are frozen
> 					freezer->state |= CGROUP_FROZEN;

Ooh, yes, now I see. Somehow I kept missing update_if_frozen().
Sometimes reading is hard :-) Thanks!

> // freezing(current) will return false,
> // since cgroup is frozen(not freezing)
> break out
> __set_current_state(TASK_RUNNING);
> //bug: the task is set to running, but it should be frozen.