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

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Date: Thu, 15 Feb 2024 13:05:30 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
 <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: Alexander Lobakin <aleksander.lobakin@...el.com>, Lorenzo Bianconi
 <lorenzo@...nel.org>, 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

Alexander Lobakin <aleksander.lobakin@...el.com> writes:

> 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.

Did you actually manage to trigger this? pool->cpuid is only set for the
system page pool instance which is never destroyed; so this seems a very
theoretical concern?

I guess we could still do this in case we find other uses for setting
the cpuid; I don't think the addition of the READ_ONCE() will have any
measurable overhead on the common arches?

-Toke