Re: [PATCH] freezer, sched: report the frozen task stat as 'D'

[Chen Ridong <chenridong@huaweicloud.com>]

On 2024/11/15 0:44, Tejun Heo wrote:
> Hello,
> 
> On Thu, Nov 14, 2024 at 03:47:58PM +0800, Chen Ridong wrote:
>> On 2024/11/13 22:34, Valentin Schneider wrote:
>>> On 11/11/24 13:54, Chen Ridong wrote:
>>>> From: Chen Ridong <chenridong@huawei.com>
>>>>
>>>> Before the commit f5d39b020809 ("freezer,sched: Rewrite core freezer
>>>> logic"), the frozen task stat was reported as 'D' in cgroup v1.
>>>> However, after rewriting core freezer logic, the frozen task stat is
>>>> reported as 'R'. This is confusing, especially when a task with stat of
>>>> 'S' is frozen.
>>>>
>>>> This can be reproduced as bellow step:
>>>> cd /sys/fs/cgroup/freezer/
>>>> mkdir test
>>>> sleep 1000 &
>>>> [1] 739         // task whose stat is 'S'
>>>> echo 739 > test/cgroup.procs
>>>> echo FROZEN > test/freezer.state
>>>> ps -aux | grep 739
>>>> root     739  0.1  0.0   8376  1812 pts/0    R    10:56   0:00 sleep 1000
>>>>
>>>> As shown above, a task whose stat is 'S' was changed to 'R' when it was
>>>> frozen. To solve this issue, simply maintain the same reported state as
>>>> before the rewrite.
> 
> The whole point of the freezer rewrite was preventing userspace from causing
> arbitrary and indefinite D states which leads to all sorts of problems. The
> tasks in cgroup2 freezer are *not* in uninterruptible sleeps. They are in
> task stop loops and thus can be killed, ptraced and so on. It *should*
> report S.
> 
> Thanks.
> 

Hi, Tj, There is no ambiguity what cgroup v2 shows. However, in cgroup
v1, the frozen tasks are reported as 'R'.  Do you think this is reseanable?

Thanks,
Ridong