linux-kernel - Re: [PATCH] cgroup_freezer: cgroup

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Message-ID: <ZVokO6_4o07FU0xP@slm.duckdns.org>
Date:   Sun, 19 Nov 2023 05:05:31 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Tim Van Patten <timvp@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, markhas@...gle.com,
        Tim Van Patten <timvp@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Zefan Li <lizefan.x@...edance.com>, cgroups@...r.kernel.org
Subject: Re: [PATCH] cgroup_freezer: cgroup_freezing: Check if not frozen

On Wed, Nov 15, 2023 at 09:20:43AM -0700, Tim Van Patten wrote:
> From: Tim Van Patten <timvp@...gle.com>
> 
> __thaw_task() was recently updated to warn if the task being thawed was
> part of a freezer cgroup that is still currently freezing:
> 
> 	void __thaw_task(struct task_struct *p)
> 	{
> 	...
> 		if (WARN_ON_ONCE(freezing(p)))
> 			goto unlock;
> 
> This has exposed a bug in cgroup1 freezing where when CGROUP_FROZEN is
> asserted, the CGROUP_FREEZING bits are not also cleared at the same
> time. Meaning, when a cgroup is marked FROZEN it continues to be marked
> FREEZING as well. This causes the WARNING to trigger, because
> cgroup_freezing() thinks the cgroup is still freezing.
> 
> There are two ways to fix this:
> 
> 1. Whenever FROZEN is set, clear FREEZING for the cgroup and all
> children cgroups.
> 2. Update cgroup_freezing() to also verify that FROZEN is not set.
> 
> This patch implements option (2), since it's smaller and more
> straightforward.
> 
> Signed-off-by: Tim Van Patten <timvp@...gle.com>

Applied to cgroup/for-6.7-fixes.

Thanks.

-- 
tejun