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

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Date:   Tue, 11 Jun 2019 17:21:39 +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 15:50 +1000, Benjamin Herrenschmidt wrote:
> On Sat, 2019-06-08 at 11:05 +0200, Borislav Petkov wrote:
> > On Sat, Jun 08, 2019 at 10:16:11AM +1000, Benjamin Herrenschmidt wrote:
> > > Those IP blocks don't need any SW coordination at runtime. The drivers
> > > don't share data nor communicate with each other. There is absolultely
> > > no reason to go down that path.
> > 
> > Let me set one thing straight: the EDAC "subsystem" if you will - or
> > that pile of code which does error counting and reporting - has its
> > limitations in supporting one EDAC driver per platform. And whenever we
> > have two drivers loadable on a platform, we have to do dirty hacks like
> > 
> >   301375e76432 ("EDAC: Add owner check to the x86 platform drivers")
> > 
> > What that means is, that if you need to call EDAC logging routines or
> > whatnot from two different drivers, there's no locking, no nothing. So
> > it might work or it might set your cat on fire.
> 
> Should we fix that then instead ? What are the big issues with adding
> some basic locking ? being called from NMIs ?
> 
> If the separate drivers operate on distinct counters I don't see a big
> problem there.

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...

Cheers,
Ben.