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

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Thu, 15 Feb 2024 13:05:30 +0100

Alexander Lobakin <[email-masked]> 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