netdev - Re: [net] net/tls: missing received data after fast remote close

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Date:   Wed, 18 Nov 2020 08:23:36 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vadim Fedorenko <vfedorenko@...ek.ru>
Cc:     Boris Pismenny <borisp@...dia.com>,
        Aviad Yehezkel <aviadye@...dia.com>, netdev@...r.kernel.org
Subject: Re: [net] net/tls: missing received data after fast remote close

On Wed, 18 Nov 2020 02:47:24 +0000 Vadim Fedorenko wrote:
> >>>> This behavior differs from plain TCP socket and
> >>>> leads to special treating in user-space. Patch unpauses parser
> >>>> directly if we have unparsed data in tcp receive queue.  
> >>> Sure, but why is the parser paused? Does it pause itself on FIN?  
> >> No, it doesn't start even once. The trace looks like:
> >>
> >> tcp_recvmsg is called
> >> tcp_recvmsg returns 1 (Change Cipher Spec record data)
> >> tls_setsockopt is called
> >> tls_setsockopt returns
> >> tls_recvmsg is called
> >> tls_recvmsg returns 0
> >> __strp_recv is called
> >> stack
> >>           __strp_recv+1
> >>           tcp_read_sock+169
> >>           strp_read_sock+104
> >>           strp_work+68
> >>           process_one_work+436
> >>           worker_thread+80
> >>           kthread+276
> >>           ret_from_fork+34tls_read_size called
> >>
> >> So it looks like strp_work was scheduled after tls_recvmsg and
> >> nothing triggered parser because all the data was received before
> >> tls_setsockopt ended the configuration process.  
> > Um. That makes me think we need to flush_work() on the strparser after
> > we configure rx tls, no? Or __unpause at the right time instead of
> > dealing with the async nature of strp_check_rcv()?  
> I'm not sure that flush_work() will do right way in this case. Because:
> 1. The work is idle after tls_sw_strparser_arm()

Not sure what you mean by idle, it queues the work via strp_check_rcv().

> 2. The strparser needs socket lock to do it's work - that could be a
> deadlock because setsockopt_conf already holds socket lock. I'm not
> sure that it's a good idea to unlock socket just to wait the strparser.

Ack, I meant in do_tls_setsockopt() after the lock is released.

> The async nature of parser is OK for classic HTTPS server/client case
> because it's very good to have parsed record before actual call to recvmsg
> or splice_read is done. The code inside the loop in tls_wait_data is slow
> path - maybe just move the check and the __unpause in this slow path?

Yeah, looking closer this problem can arise after we start as well :/

How about we move the __unparse code into the loop tho? Seems like this
could help with latency. Right now AFAICT we get a TCP socket ready
notification, which wakes the waiter for no good reason and makes
strparser queue its work, the work then will call tls_queue() ->
data_ready waking the waiting thread second time this time with the
record actually parsed.

Did I get that right? Should the waiter not cancel the work on the
first wake up and just kick of the parsing itself?