linux-kernel - Re: [PATCH net-next] page_pool: disable direct recycling based on pool->cpuid on destroy

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Date: Fri, 16 Feb 2024 18:47:33 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: "David S. Miller" <davem@...emloft.net>
CC: Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>, Lorenzo Bianconi <lorenzo@...nel.org>,
	Toke Høiland-Jørgensen <toke@...hat.com>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] page_pool: disable direct recycling based on
 pool->cpuid on destroy

From: Alexander Lobakin <aleksander.lobakin@...el.com>
Date: Thu, 15 Feb 2024 12:39:05 +0100

> Now that direct recycling is performed basing on pool->cpuid when set,
> memory leaks are possible:
> 
> 1. A pool is destroyed.
> 2. Alloc cache is emptied (it's done only once).
> 3. pool->cpuid is still set.
> 4. napi_pp_put_page() does direct recycling basing on pool->cpuid.
> 5. Now alloc cache is not empty, but it won't ever be freed.
> 
> In order to avoid that, rewrite pool->cpuid to -1 when unlinking NAPI to
> make sure no direct recycling will be possible after emptying the cache.
> This involves a bit of overhead as pool->cpuid now must be accessed
> via READ_ONCE() to avoid partial reads.
> Rename page_pool_unlink_napi() -> page_pool_disable_direct_recycling()
> to reflect what it actually does and unexport it.

PW says "Changes requested", but I don't see any in the thread, did I
miss something? :D

Thanks,
Olek