netdev - Re: [PATCH 1/2] tls: remove close callback sock unlock/lock and flush

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Message-ID: <20190628113100.597bfbe6@cakuba.netronome.com>
Date:   Fri, 28 Jun 2019 11:31:00 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     daniel@...earbox.io, ast@...nel.org, netdev@...r.kernel.org,
        edumazet@...gle.com, bpf@...r.kernel.org
Subject: Re: [PATCH 1/2] tls: remove close callback sock unlock/lock and
 flush_sync

On Fri, 28 Jun 2019 07:12:07 -0700, John Fastabend wrote:
> Yeah seems possible although never seen in my testing. So I'll
> move the test_bit() inside the lock and do a ctx check to ensure
> still have the reference.
> 
>   CPU 0 (free)           CPU 1 (wq)
> 
>   lock(sk)
>                          lock(sk)
>   set_bit()
>   cancel_work()
>   release
>                          ctx = tls_get_ctx(sk)
>                          unlikely(!ctx) <- we may have free'd 
>                          test_bit()
>                          ...
>                          release()
> 
> or
> 
>   CPU 0 (free)           CPU 1 (wq)
> 
>                          lock(sk)
>   lock(sk)
>                          ctx = tls_get_ctx(sk)
>                          unlikely(!ctx)
>                          test_bit()
>                          ...
>                          release()
>   set_bit()
>   cancel_work()
>   release

Hmm... perhaps it's cleanest to stop the work from scheduling before we
proceed?

close():
	while (!test_and_set(SHED))
		flush();

	lock(sk);
	...

We just need to move init work, no?

FWIW I never tested his async crypto stuff, I wonder if there is a way
to convince normal CPU crypto to pretend to be async?