From: Mina Almasry <almasrymina@google.com>
To: Jakub Kicinski <kuba@kernel.org>
Cc: Dragos Tatulea <dtatulea@nvidia.com>,
"davem@davemloft.net" <davem@davemloft.net>,
"pabeni@redhat.com" <pabeni@redhat.com>,
"ilias.apalodimas@linaro.org" <ilias.apalodimas@linaro.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"jacob.e.keller@intel.com" <jacob.e.keller@intel.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
Jianbo Liu <jianbol@nvidia.com>,
"edumazet@google.com" <edumazet@google.com>
Subject: Re: [RFC PATCH] net: Fix one page_pool page leak from skb_frag_unref
Date: Fri, 26 Apr 2024 21:24:09 -0700 [thread overview]
Message-ID: <CAHS8izNs-LV=6FE39sjF3V7qVfveOsOAOJ_X62TSzWpvamsS0Q@mail.gmail.com> (raw)
In-Reply-To: <20240426160859.0d85908e@kernel.org>
On Fri, Apr 26, 2024 at 4:09 PM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Thu, 25 Apr 2024 12:20:59 -0700 Mina Almasry wrote:
> > - if (recycle && napi_pp_get_page(page))
> > + if (napi_pp_get_page(page))
>
> Pretty sure you can't do that. The "recycle" here is a concurrency
> guarantee. A guarantee someone is holding a pp ref on that page,
> a ref which will not go away while napi_pp_get_page() is executing.
I don't mean to argue, but I think the get_page()/put_page() pair we
do in the page ref path is susceptible to the same issue. AFAIU it's
not safe to get_page() if another CPU can be dropping the last ref,
get_page_unless_zero() should be used instead.
Since get_page() is good in the page ref path without some guarantee,
it's not obvious to me why we need this guarantee in the pp ref path,
but I could be missing some subtlety. At any rate, if you prefer us
going down the road of reverting commit 2cc3aeb5eccc ("skbuff: Fix a
potential race while recycling page_pool packets"), I think that could
also fix the issue.
--
Thanks,
Mina
next prev parent reply other threads:[~2024-04-27 4:24 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-24 16:56 [RFC PATCH] net: Fix one page_pool page leak from skb_frag_unref Dragos Tatulea
2024-04-24 17:25 ` Dragos Tatulea
2024-04-24 22:08 ` Mina Almasry
2024-04-25 8:17 ` Dragos Tatulea
2024-04-25 19:20 ` Mina Almasry
2024-04-25 19:47 ` Dragos Tatulea
2024-04-25 20:42 ` Mina Almasry
2024-04-26 14:59 ` Dragos Tatulea
2024-04-26 19:03 ` Mina Almasry
2024-04-26 23:08 ` Jakub Kicinski
2024-04-27 4:24 ` Mina Almasry [this message]
2024-04-29 15:00 ` Jakub Kicinski
2024-05-02 20:08 ` Mina Almasry
2024-05-03 0:46 ` Jakub Kicinski
2024-04-26 23:05 ` Jakub Kicinski
2024-04-29 7:39 ` Dragos Tatulea
2024-05-01 6:20 ` Dragos Tatulea
2024-05-01 7:48 ` Mina Almasry
2024-05-01 7:58 ` Dragos Tatulea
2024-05-01 14:24 ` Jakub Kicinski
2024-05-01 14:28 ` Jakub Kicinski
2024-05-01 16:23 ` Mina Almasry
2024-04-26 23:07 ` Jakub Kicinski
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