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

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Message-ID: <4ceb0e8c-d164-4323-add0-a0770ec2afc6@kylinos.cn>
Date: Mon, 11 Aug 2025 17:54:23 +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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 Kees Cook <kees@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>,
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 Al Viro <viro@...iv.linux.org.uk>, Adrian Ratiu
 <adrian.ratiu@...labora.com>, linux-pm@...r.kernel.org, linux-mm@...ck.org,
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 linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 5/9] freezer: set default freeze priority for
 PF_SUSPEND_TASK processes

在 2025/8/11 17:46, Oleg Nesterov 写道:
> On 08/11, Zihuan Zhang wrote:
>> 在 2025/8/11 17:32, Oleg Nesterov 写道:
>>> On 08/11, Zihuan Zhang wrote:
>>>> 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.
>>> How so? sorry I don't follow.
>> The problem is in this part:
>>
>> +            if (user_only && !(p->flags & PF_KTHREAD) && round <
>> p->freeze_priority)
>> +                continue;
>>
>> PF_SUSPEND_TASK is a user process, so it meets the “needs freezing”
>> condition and todo gets incremented.
>              ^^^^^^^^^^^^^^^^^^^^^^^^^
>
> No.
> 	if (p == current || !freeze_task(p))
> 		continue;
>
> 	todo++;
>
> Again, again, freeze_task(p) returns false.
>
>> But it actually doesn’t need to freeze,
>> so resulting in an infinite loop
> I don't think so.
>
> Oleg.
Sorry, you’re right — it’s indeed unnecessary. In an earlier version, I 
incremented the counter before the continue, but I later removed that 
and forgot about it.