netdev - Re: [Bug report] NFS patch breaks TLS device-offloaded TX zerocopy

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Message-ID: <c1096b57-a03f-4fa2-b61f-7418f2304618@gmail.com>
Date: Mon, 12 Aug 2024 16:15:35 +0300
From: Tariq Toukan <ttoukan.linux@...il.com>
To: Sagi Grimberg <sagi@...mberg.me>, Christoph Hellwig <hch@....de>,
 Anna Schumaker <Anna.Schumaker@...app.com>,
 Trond Myklebust <trondmy@...nel.org>, linux-nfs@...r.kernel.org,
 Boris Pismenny <borisp@...dia.com>, John Fastabend
 <john.fastabend@...il.com>, Jakub Kicinski <kuba@...nel.org>,
 Maxim Mikityanskiy <maxtram95@...il.com>, David Howells
 <dhowells@...hat.com>, Sabrina Dubroca <sd@...asysnail.net>,
 Mina Almasry <almasrymina@...gle.com>
Cc: Saeed Mahameed <saeedm@...dia.com>, Gal Pressman <gal@...dia.com>,
 Networking <netdev@...r.kernel.org>, Paolo Abeni <pabeni@...hat.com>,
 Eric Dumazet <edumazet@...gle.com>, "David S. Miller" <davem@...emloft.net>,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
 Leon Romanovsky <leon@...nel.org>, Tariq Toukan <tariqt@...dia.com>,
 drort@...dia.com
Subject: Re: [Bug report] NFS patch breaks TLS device-offloaded TX zerocopy

On 11/08/2024 21:33, Sagi Grimberg wrote:
> 
> 
> 
> On 11/08/2024 14:21, Tariq Toukan wrote:
>>
>>
>> On 06/08/2024 13:07, Tariq Toukan wrote:
>>>
>>>
>>> On 06/08/2024 11:09, Sagi Grimberg wrote:
>>>>
>>>>
>>>>
>>>> On 06/08/2024 7:43, Tariq Toukan wrote:
>>>>>
>>>>>
>>>>> On 05/08/2024 14:43, Sagi Grimberg wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 05/08/2024 13:40, Tariq Toukan wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> A recent patch [1] to 'fs' broke the TX TLS device-offloaded flow 
>>>>>>> starting from v6.11-rc1.
>>>>>>>
>>>>>>> The kernel crashes. Different runs result in different kernel 
>>>>>>> traces.
>>>>>>> See below [2].
>>>>>>> All of them disappear once patch [1] is reverted.
>>>>>>>
>>>>>>> The issues appears only with "sendfile on and zerocopy on".
>>>>>>> We couldn't repro with "sendfile off", or with "sendfile on and 
>>>>>>> zerocopy off".
>>>>>>>
>>>>>>> The repro test is as simple as a repeated client/server 
>>>>>>> communication (wrk/nginx), with sendfile on and zc on, and with 
>>>>>>> "tls-hw-tx-offload: on".
>>>>>>>
>>>>>>> $ for i in `seq 10`; do wrk -b::2:2:2:3 -t10 -c100 -d15 --timeout 
>>>>>>> 5s https://[::2:2:2:2]:20448/16000b.img; done
>>>>>>>
>>>>>>> We can provide more details if needed, to help with the analysis 
>>>>>>> and debug.
>>>>>>
>>>>>> Does tls sw (i.e. no offload) also break?
>>>>>>
>>>>>
>>>>> No it doesn't.
>>>>> Only the "sendfile with ZC" flow of the TX device-offloaded TLS.
>>>>
>>>
>>> Adding Maxim Mikityanskiy, he might have some insights.
>>>
>>>> Not familiar with the TLS offload code, are there any assumptions on 
>>>> PAGE_SIZE contig buffers? Or assumptions on individual
>>>> page references/lifetime?
>>>>
>>>> The sporadic panics you reported look like a result of memory 
>>>> corruption or use-after-free conditions.
>>
>> You can find the original patch that implements it here:
>> c1318b39c7d3 tls: Add opt-in zerocopy mode of sendfile()
>>
>> In this flow (sendfile + ZC), page is shared for kernel and userspace, 
>> and the extra copy is skipped.
>>
>> There were a few code changes in this area since the feature was 
>> introduced.
>> Adding relevant ppl, including David Howells <dhowells@...hat.com>, 
>> who removed the sendpage() routine and added MSG_SPLICE_PAGES support 
>> to tls_device.
> 
> Tariq,
> 
> Can you explain where in your test is NFS used? Is the nginx server runs 
> on an NFS mount?

I checked with the team.
The requested file, as well as the wrk and nginx apps, all reside on an 
NFS mount.