netdev - Re: [PATCH 4/4] net/tls: implement ->read

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Date: Wed, 21 Jun 2023 08:44:56 +0200
From: Hannes Reinecke <hare@...e.de>
To: Jakub Kicinski <kuba@...nel.org>, Sagi Grimberg <sagi@...mberg.me>
Cc: Christoph Hellwig <hch@....de>, Keith Busch <kbusch@...nel.org>,
 linux-nvme@...ts.infradead.org, Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
 Boris Pismenny <boris.pismenny@...il.com>
Subject: Re: [PATCH 4/4] net/tls: implement ->read_sock()

On 6/20/23 19:08, Jakub Kicinski wrote:
> On Tue, 20 Jun 2023 16:21:22 +0300 Sagi Grimberg wrote:
>>> +	err = tls_rx_reader_lock(sk, ctx, true);
>>> +	if (err < 0)
>>> +		return err;
>>
>> Unlike recvmsg or splice_read, the caller of read_sock is assumed to
>> have the socket locked, and tls_rx_reader_lock also calls lock_sock,
>> how is this not a deadlock?
> 
> Yeah :|
> 
>> I'm not exactly clear why the lock is needed here or what is the subtle
>> distinction between tls_rx_reader_lock and what lock_sock provides.
> 
> It's a bit of a workaround for the consistency of the data stream.
> There's bunch of state in the TLS ULP and waiting for mem or data
> releases and re-takes the socket lock. So to stop the flow annoying
> corner case races I slapped a lock around all of the reader.
> 
> IMHO depending on the socket lock for anything non-trivial and outside
> of the socket itself is a bad idea in general.
> 
> The immediate need at the time was that if you did a read() and someone
> else did a peek() at the same time from a stream of A B C D you may read
> A D B C.

Leaving me ever so confused.

read_sock() is a generic interface; we cannot require a protocol 
specific lock before calling it.

What to do now?
Drop the tls_rx_read_lock from read_sock() again?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@...e.de                              +49 911 74053 688
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