linux-kernel - Re: [next] cgroup,freezer: fix incomplete freezing when attaching tasks

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Message-ID: <sfmtpva4z4jxrlmmeyigz4n7wozfveii3cuaks3s4dgf6noyfg@gutbimmbjfbb>
Date: Wed, 18 Jun 2025 10:42:08 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Chen Ridong <chenridong@...weicloud.com>
Cc: tj@...nel.org, hannes@...xchg.org, rafael.j.wysocki@...el.com, 
	mingo@...nel.org, peterz@...radead.org, cgroups@...r.kernel.org, 
	linux-kernel@...r.kernel.org, lujialin4@...wei.com, chenridong@...wei.com
Subject: Re: [next] cgroup,freezer: fix incomplete freezing when attaching
 tasks

On Wed, Jun 18, 2025 at 07:32:17AM +0000, Chen Ridong <chenridong@...weicloud.com> wrote:
> From: Chen Ridong <chenridong@...wei.com>
> 
> An issue was found:

An obligatory reminder to move to freezer in the unifier hierarchy if
possible. Thanks for the fix though.

> 
> 	# cd /sys/fs/cgroup/freezer/
> 	# mkdir test
> 	# echo FROZEN > test/freezer.state
> 	# cat test/freezer.state
> 	FROZEN
> 	# sleep 1000 &
> 	[1] 863
> 	# echo 863 > test/cgroup.procs
> 	# cat test/freezer.state
> 	FREEZING
> 
> When tasks are migrated to a frozen cgroup, the freezer fails to
> immediately freeze the tasks, causing the cgroup to remain in the
> "FREEZING".
> 
> The freeze_task() function is called before clearing the CGROUP_FROZEN
> flag. This causes the freezing() check to incorrectly return false,
> preventing __freeze_task() from being invoked for the migrated task.
> 
> To fix this issue, clear the CGROUP_FROZEN state before calling
> freeze_task().
> 
> Fixes: f5d39b020809 ("freezer,sched: Rewrite core freezer logic")
> Reported-by: Zhong Jiawei <zhongjiawei1@...wei.com>
> Signed-off-by: Chen Ridong <chenridong@...wei.com>
> ---
>  kernel/cgroup/legacy_freezer.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)

Acked-by: Michal Koutný <mkoutny@...e.com>

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