netdev - Re: [BUG] pfifo_fast may cause out-of-order CAN frame transmission

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Message-ID: <13e8950e8537e549f6afb6e254ec75a7462ce648.camel@redhat.com>
Date:   Thu, 06 Feb 2020 14:21:16 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Ahmad Fatoum <a.fatoum@...gutronix.de>, netdev@...r.kernel.org,
        linux-can@...r.kernel.org,
        Pengutronix Kernel Team <kernel@...gutronix.de>
Subject: Re: [BUG] pfifo_fast may cause out-of-order CAN frame transmission

On Tue, 2020-02-04 at 17:25 +0100, Ahmad Fatoum wrote:
> Hello Paolo,
> 
> On 1/20/20 5:06 PM, Ahmad Fatoum wrote:
> > Hello Paolo,
> > 
> > On 1/16/20 1:40 PM, Paolo Abeni wrote:
> > > I'm sorry for this trial & error experience. I tried to reproduce the
> > > issue on top of the vcan virtual device, but it looks like it requires
> > > the timing imposed by a real device, and it's missing here (TL;DR: I
> > > can't reproduce the issue locally).
> > 
> > No worries. I don't mind testing.
> > 
> > > Code wise, the 2nd patch closed a possible race, but it dumbly re-
> > > opened the one addressed by the first attempt - the 'empty' field must
> > > be cleared prior to the trylock operation, or we may end-up with such
> > > field set and the queue not empty.
> > > 
> > > So, could you please try the following code?
> > 
> > Unfortunately, I still see observe reodering.
> 
> Any news?

I'm unable to find any better solution than a revert. That will cost
some small performace regression, so I'm a bit reluctant to go ahead.
If there is agreement I can post the revert.

Cheers,

Paolo