netdev - Re: Report on abnormal behavior of "page

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Date: Wed, 31 Jan 2024 16:56:26 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Justin Lai <justinlai0215@...ltek.com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>
Subject: Re: Report on abnormal behavior of "page_pool" API

On 2024/1/31 15:31, Justin Lai wrote:
> To whom it may concern,
> 
> I hope this email finds you well. I am writing to report a behavior
> which seems to be abnormal.
> 
> When I remove the module, I call page_pool_destroy() to release the

Which module?

> page_pool, but this message appears, page_pool_release_retry() stalled 
> pool shutdown 1024 inflight 120 sec. Then I tried to return the page to
> page_pool before calling page_pool_destroy(), so I called
> page_pool_put_full_page() first, but after doing so, this message was
> printed, page_pool_empty_ring() page_pool refcnt 0 violation, and the

As we have "page_ref_count(page) == 1" checking to allow recycling page
in pool->ring:
https://elixir.bootlin.com/linux/v6.8-rc2/source/net/core/page_pool.c#L654

It seems somebody is still using the page and manipulating _refcount while
the page is sitting in the pool->ring?


> computer crashed.
> 
> I would like to ask what could be causing this and how I should fix it.

Not sure if you read the below doc for page_pool, understanding the internal
detail and the API usages may help you debuging the problem:
Documentation/networking/page_pool.rst

> 
> The information on my working environment is: Ubuntu23.10,
> linux kernel 6.4, 6.5, 6.6
> 
> Thank you for your time and efforts, I am looking forward to your reply.
> 
> Best regards,
> Justin
> 
> .
>