linux-kernel - Re: 4.4.1 regression from 4.1.x: Soekris net5501 crash in IRQ after mfgpt timer initialization

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Date:	Tue, 2 Feb 2016 16:51:38 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Nix <nix@...eri.org.uk>
cc:	Andres Salomon <dilinger@...ued.net>, arnd@...db.de,
	linux-kernel@...r.kernel.org
Subject: Re: 4.4.1 regression from 4.1.x: Soekris net5501 crash in IRQ after
 mfgpt timer initialization

On Tue, 2 Feb 2016, Nix wrote:

> On 2 Feb 2016, Thomas Gleixner said:
> 
> > On Tue, 2 Feb 2016, Nix wrote:
> >
> >> [Cc:ed Thomas on the vague hope that maybe this is osmething to do with
> >>  the IRQ subsystem in general, though I doubt it, since only the one
> >>  machine is crashing for me: it's probably the CS5531's interactions
> >>  with said subsystem at fault.]
> >
> > Kinda. That driver does the following:
> >
> >        setup the irq in CS5531
> >
> >        request the interrupt to install the handler
> >
> >        register the clockevents device
> 
> It seems like it should do those in the opposite order, really, or at
> the very least do the IRQ setup last!

Yes.
 
> > So the interrupt hits before the clockevent device is registered and the event
> > handler is installed. So mfgpt_tick() will happily call a null pointer.
> >
> > The patch below should fix^Wwork around the issue.
> 
> The fairly trivial code motion below also seems to work, and may be more
> like an actual fix, though I'm a bit horrified that it's this simple. I
> may well have moved too much and unknowingly violated some invariant.

I was lazy and did not do this, because it wreckages the error pathes. So I
went for the workaround in the hope that the authors of that stuff will take
care :)

Thanks,

	tglx