netdev - Re: [PATCH net-next v3] page_pool: avoid infinite loop to schedule delayed worker

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Message-ID: <CAHS8izOcLnt3SXzfbSA_vqno0R1SaBbXq-U8_LtRv64Bj7tUSQ@mail.gmail.com>
Date: Fri, 14 Feb 2025 12:27:28 -0800
From: Mina Almasry <almasrymina@...gle.com>
To: Jason Xing <kerneljasonxing@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, 
	pabeni@...hat.com, horms@...nel.org, hawk@...nel.org, 
	ilias.apalodimas@...aro.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3] page_pool: avoid infinite loop to schedule
 delayed worker

On Thu, Feb 13, 2025 at 10:43 PM Jason Xing <kerneljasonxing@...il.com> wrote:
>
> We noticed the kworker in page_pool_release_retry() was waken
> up repeatedly and infinitely in production because of the
> buggy driver causing the inflight less than 0 and warning
> us in page_pool_inflight()[1].
>
> Since the inflight value goes negative, it means we should
> not expect the whole page_pool to get back to work normally.
>
> This patch mitigates the adverse effect by not rescheduling
> the kworker when detecting the inflight negative in
> page_pool_release_retry().
>
> [1]
> [Mon Feb 10 20:36:11 2025] ------------[ cut here ]------------
> [Mon Feb 10 20:36:11 2025] Negative(-51446) inflight packet-pages
> ...
> [Mon Feb 10 20:36:11 2025] Call Trace:
> [Mon Feb 10 20:36:11 2025]  page_pool_release_retry+0x23/0x70
> [Mon Feb 10 20:36:11 2025]  process_one_work+0x1b1/0x370
> [Mon Feb 10 20:36:11 2025]  worker_thread+0x37/0x3a0
> [Mon Feb 10 20:36:11 2025]  kthread+0x11a/0x140
> [Mon Feb 10 20:36:11 2025]  ? process_one_work+0x370/0x370
> [Mon Feb 10 20:36:11 2025]  ? __kthread_cancel_work+0x40/0x40
> [Mon Feb 10 20:36:11 2025]  ret_from_fork+0x35/0x40
> [Mon Feb 10 20:36:11 2025] ---[ end trace ebffe800f33e7e34 ]---
> Note: before this patch, the above calltrace would flood the
> dmesg due to repeated reschedule of release_dw kworker.
>
> Signed-off-by: Jason Xing <kerneljasonxing@...il.com>

Thanks Jason,

Reviewed-by: Mina Almasry <almasrymina@...gle.com>

When you find the root cause of the driver bug, if you can think of
ways to catch it sooner in the page_pool or prevent drivers from
triggering it, please do consider sending improvements upstream.
Thanks!

-- 
Thanks,
Mina