linux-kernel - Re: [RFC PATCH v1 0/9] freezer: Introduce freeze priority model to address process dependency issues

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Message-ID: <bef49dcb-8619-4448-b8d7-6dca3a6cb456@kylinos.cn>
Date: Fri, 15 Aug 2025 16:27:18 +0800
From: Zihuan Zhang <zhangzihuan@...inos.cn>
To: Peter Zijlstra <peterz@...radead.org>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>, Oleg Nesterov
 <oleg@...hat.com>, David Hildenbrand <david@...hat.com>,
 Michal Hocko <mhocko@...e.com>, Jonathan Corbet <corbet@....net>,
 Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
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 len brown <len.brown@...el.com>, pavel machek <pavel@...nel.org>,
 Kees Cook <kees@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
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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 0/9] freezer: Introduce freeze priority model to
 address process dependency issues

在 2025/8/14 22:37, Peter Zijlstra 写道:
> On Thu, Aug 07, 2025 at 08:14:09PM +0800, Zihuan Zhang wrote:
>
>> Freeze Window Begins
>>
>>      [process A] - epoll_wait()
>>          │
>>          ▼
>>      [process B] - event source (already frozen)
>>
> Can we make epoll_wait() TASK_FREEZABLE? AFAICT it doesn't hold any
> resources, it just sits there waiting for stuff.

Based on the code, it’s ep_poll() that puts the task into the D state, 
most likely due to I/O or lower-level driver behavior. In fs/eventpoll.c:

Line:2097 __set_current_state 
<https://elixir.bootlin.com/linux/v6.16/C/ident/__set_current_state>(TASK_INTERRUPTIBLE 
<https://elixir.bootlin.com/linux/v6.16/C/ident/TASK_INTERRUPTIBLE>);

Simply changing the task state may not actually address the root cause. 
Currently, our approach is to identify tasks that are more likely to 
cause such issues and freeze them earlier or later in the process to 
avoid conflicts.