linux-kernel - Re: [RFC PATCH v1 5/9] freezer: set default freeze priority for PF_SUSPEND

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Message-ID: <0754e3e3-9c47-47d5-81d9-4574e5b413bc@kylinos.cn>
Date: Mon, 11 Aug 2025 17:25:10 +0800
From: Zihuan Zhang <zhangzihuan@...inos.cn>
To: Oleg Nesterov <oleg@...hat.com>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, David Hildenbrand <david@...hat.com>,
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Subject: Re: [RFC PATCH v1 5/9] freezer: set default freeze priority for
 PF_SUSPEND_TASK processes

在 2025/8/8 22:39, Oleg Nesterov 写道:
> On 08/07, Zihuan Zhang wrote:
>> --- a/kernel/power/process.c
>> +++ b/kernel/power/process.c
>> @@ -147,6 +147,7 @@ int freeze_processes(void)
>>
>>   	pm_wakeup_clear(0);
>>   	pm_freezing = true;
>> +	freeze_set_default_priority(current, FREEZE_PRIORITY_NEVER);
> But why?
>
> Again, freeze_task() will return false anyway, this process is
> PF_SUSPEND_TASK.

I  think there is resaon put it here. For example, systemd-sleep is a 
user-space process that executes the suspend flow.

  If we don’t set its freeze priority explicitly, our current code may 
end up with this user process being the last one that cannot freeze.

Of course, we could adjust the code logic to handle it differently, but 
in our model its freeze priority is considered the lowest, so setting it 
here ensures consistent behavior.

>> @@ -218,6 +219,7 @@ void thaw_processes(void)
>>   	WARN_ON(!(curr->flags & PF_SUSPEND_TASK));
>>   	curr->flags &= ~PF_SUSPEND_TASK;
>>
>> +	freeze_set_default_priority(current, FREEZE_PRIORITY_NORMAL);
>>   	usermodehelper_enable();
> What if current->freeze_priority was changed via
> /proc/pid/freeze_priority you add in 9/9 ?

Sorry, my oversight. You are right — in this case we probably should not 
allow user space to change the freeze_priority of a PF_SUSPEND_TASK. 
This would avoid unintended behavior during suspend.

>
> Oleg.
>