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Date:   Wed, 14 Jun 2023 21:20:31 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     Liang Chen <liangchen.linux@gmail.com>
Cc:     hawk@kernel.org, ilias.apalodimas@linaro.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        davem@davemloft.net, edumazet@google.com, pabeni@redhat.com
Subject: Re: [PATCH net-next] page pool: not return page to alloc cache
 during pool destruction
Message-ID: <20230614212031.7e1b6893@kernel.org>
In-Reply-To: <20230615013645.7297-1-liangchen.linux@gmail.com>
References: <20230615013645.7297-1-liangchen.linux@gmail.com>
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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?