Received-SPF: pass (google.com: domain of linux-kernel+bounces-66859-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
To: Alexander Lobakin <aleksander.lobakin@intel.com>, "David S. Miller"
 <davem@davemloft.net>, Eric Dumazet <edumazet@google.com>, Jakub Kicinski
 <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>
Cc: Alexander Lobakin <aleksander.lobakin@intel.com>, Lorenzo Bianconi
 <lorenzo@kernel.org>, netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next] page_pool: disable direct recycling based on
 pool->cpuid on destroy
In-Reply-To: <20240215113905.96817-1-aleksander.lobakin@intel.com>
References: <20240215113905.96817-1-aleksander.lobakin@intel.com>
Date: Thu, 15 Feb 2024 13:05:30 +0100
Message-ID: <87v86qc4qd.fsf@toke.dk>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain

Alexander Lobakin <aleksander.lobakin@intel.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