netdev - Re: [PATCH net-next v1] page_pool: avoid infinite loop to schedule delayed worker

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Message-ID: <CAHS8izMznEB7TWkc4zxBhFF+8JVmstFoRfqfsRLOOMbcuUoRRA@mail.gmail.com>
Date: Tue, 11 Feb 2025 18:37:22 -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, hawk@...nel.org, ilias.apalodimas@...aro.org, 
	horms@...nel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v1] page_pool: avoid infinite loop to schedule
 delayed worker

On Mon, Feb 10, 2025 at 5:10 AM Jason Xing <kerneljasonxing@...il.com> wrote:
>
> If the buggy driver causes the inflight less than 0 [1] and warns

How does a buggy driver trigger this?

> us in page_pool_inflight(), it means we should not expect the
> whole page_pool to get back to work normally.
>
> We noticed the kworker is waken up repeatedly and infinitely[1]
> in production. If the page pool detect the error happening,
> probably letting it go is a better way and do not flood the
> var log messages. This patch mitigates the adverse effect.
>
> [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 ]---
>
> Signed-off-by: Jason Xing <kerneljasonxing@...il.com>
> ---
>  net/core/page_pool.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index 1c6fec08bc43..8e9f5801aabb 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -1167,7 +1167,7 @@ void page_pool_destroy(struct page_pool *pool)
>         page_pool_disable_direct_recycling(pool);
>         page_pool_free_frag(pool);
>
> -       if (!page_pool_release(pool))
> +       if (page_pool_release(pool) <= 0)
>                 return;

Isn't it the condition in page_pool_release_retry() that you want. to
modify? That is the one that handles whether the worker keeps spinning
no?

I also wonder also whether if the check in page_pool_release() itself
needs to be:

if (inflight < 0)
  __page_pool_destroy();

otherwise the pool will never be destroyed no?

-- 
Thanks,
Mina