linux-kernel - Re: [PATCH 2/2] edac: add support for Amazon's Annapurna Labs EDAC

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Message-ID: <6df5a17bb1c900dc69b991171e55632f40d9426f.camel@kernel.crashing.org>
Date:   Wed, 12 Jun 2019 08:25:52 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     James Morse <james.morse@....com>,
        "Hawa, Hanna" <hhhawa@...zon.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        "paulmck@...ux.ibm.com" <paulmck@...ux.ibm.com>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "nicolas.ferre@...rochip.com" <nicolas.ferre@...rochip.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "Shenhar, Talel" <talel@...zon.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Chocron, Jonathan" <jonnyc@...zon.com>,
        "Krupnik, Ronen" <ronenk@...zon.com>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "Hanoch, Uri" <hanochu@...zon.com>
Subject: Re: [PATCH 2/2] edac: add support for Amazon's Annapurna Labs EDAC

On Tue, 2019-06-11 at 13:56 +0200, Borislav Petkov wrote:
> On Tue, Jun 11, 2019 at 05:21:39PM +1000, Benjamin Herrenschmidt wrote:
> > So looking again ... all the registration/removal of edac devices seem
> > to already be protected by mutexes, so that's not a problem.
> > 
> > Tell me more about what specific races you think we might have here,
> > I'm not sure I follow...
> 
> Well, as I said "it might work or it might set your cat on fire." For
> example, one of the error logging paths is edac_mc_handle_error() and
> that thing mostly operates using the *mci pointer which should be ok
> but then it calls the "trace_mc_event" tracepoint and I'd suppose that
> tracepoints can do lockless but I'm not sure.

Yes, we would be in a world of pain already if tracepoints couldn't
handle concurrency :-)

> So what needs to happen is for paths which weren't called by multiple
> EDAC agents in parallel but need to get called in parallel now due to
> ARM drivers wanting to do that, to get audited that they're safe.

That's the thing, I don't think we have such path. We are talking about
having separate L1/L2 vs. MC drivers, they don't overlap.

> Situation is easy if you have one platform driver where you can
> synchronize things in the driver but since you guys need to do separate
> drivers for whatever reason, then that would need to be done prior.
> 
> Makes more sense?

Sort-of... I still don't see a race in what we propose but I might be
missing something subtle. We are talking about two drivers for two
different IP blocks updating different counters etc...

Cheers,
Ben.