netdev - Re: [PATCHv6 0/5] net/tls: fixes for NVMe-over-TLS

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Date: Mon, 3 Jul 2023 15:46:35 +0200
From: Hannes Reinecke <hare@...e.de>
To: Sagi Grimberg <sagi@...mberg.me>, David Howells <dhowells@...hat.com>
Cc: Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>,
 linux-nvme@...ts.infradead.org, Jakub Kicinski <kuba@...nel.org>,
 Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
 netdev@...r.kernel.org
Subject: Re: [PATCHv6 0/5] net/tls: fixes for NVMe-over-TLS

On 7/3/23 15:42, Sagi Grimberg wrote:
> 
>>>> Hannes Reinecke <hare@...e.de> wrote:
>>>>
>>>>>> 'discover' and 'connect' works, but when I'm trying to transfer data
>>>>>> (eg by doing a 'mkfs.xfs') the whole thing crashes horribly in
>>>>>> sock_sendmsg() as it's trying to access invalid pages :-(
>>>>
>>>> Can you be more specific about the crash?
>>>
>>> Hannes,
>>>
>>> See:
>>> [PATCH net] nvme-tcp: Fix comma-related oops
>>
>> Ah, right. That solves _that_ issue.
>>
>> But now I'm deadlocking on the tls_rx_reader_lock() (patched as to 
>> your suggestion). Investigating.
> 
> Are you sure it is a deadlock? or maybe you returned EAGAIN and nvme-tcp
> does not interpret this as a transient status and simply returns from
> io_work?
> 
>> But it brought up yet another can of worms: what _exactly_ is the 
>> return value of ->read_sock()?
>>
>> There are currently two conflicting use-cases:
>> -> Ignore the return value, and assume errors etc are signalled
>>     via 'desc.error'.
>>     net/strparser/strparser.c
>>     drivers/infiniband/sw/siw
>>     drivers/scsi/iscsi_tcp.c
>> -> use the return value of ->read_sock(), ignoring 'desc.error':
>>     drivers/nvme/host/tcp.c
>>     net/ipv4/tcp.c
>> So which one is it?
>> Needless to say, implementations following the second style do not
>> set 'desc.error', causing any errors there to be ignored for callers
>> from the first style...
> 
> I don't think ignoring the return value of read_sock makes sense because
> it can fail outside of the recv_actor failures.
> 
Oh, but it's not read_actor which is expected to set desc.error.
Have a look at 'strp_read_sock()':

         /* sk should be locked here, so okay to do read_sock */
         sock->ops->read_sock(strp->sk, &desc, strp_recv);

         desc.error = strp->cb.read_sock_done(strp, desc.error);

it's the ->read_sock() callback which is expected to set desc.error.

> But to be on the safe side, perhaps you can both return an error and set
> desc.error?
> 
But why? We can easily make ->read_sock() a void function, then it's 
obvious that you can't check the return value.

Cheers,

Hannes