netdev - Re: [PATCH net-next] page pool: not return page to alloc cache during pool destruction

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Date: Wed, 14 Jun 2023 21:20:31 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Liang Chen <liangchen.linux@...il.com>
Cc: hawk@...nel.org, ilias.apalodimas@...aro.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
 pabeni@...hat.com
Subject: Re: [PATCH net-next] page pool: not return page to alloc cache
 during pool destruction

On Thu, 15 Jun 2023 09:36:45 +0800 Liang Chen wrote:
> When destroying a page pool, the alloc cache and recycle ring are emptied.
> If there are inflight pages, the retry process will periodically check the
> recycle ring for recently returned pages, but not the alloc cache (alloc
> cache is only emptied once). As a result, any pages returned to the alloc
> cache after the page pool destruction will be stuck there and cause the
> retry process to continuously look for inflight pages and report warnings.
> 
> To safeguard against this situation, any pages returning to the alloc cache
> after pool destruction should be prevented.

Let's hear from the page pool maintainers but I think the driver 
is supposed to prevent allocations while pool is getting destroyed.
Perhaps we can add DEBUG_NET_WARN_ON_ONCE() for this condition to
prevent wasting cycles in production builds?