linux-kernel - Re: [WARNING: A/V UNSCANNABLE][Merge tag 'media/v4.11-1' of git] ff58d005cd: BUG: unable to handle kernel NULL pointer dereference at 0000039c

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Message-ID: <20170227162639.GN21809@atomide.com>
Date:   Mon, 27 Feb 2017 08:26:39 -0800
From:   Tony Lindgren <tony@...mide.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Ingo Molnar <mingo@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Ruslan Ruslichenko <rruslich@...co.com>,
        "linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
        kernel@...inux.com, Sean Young <sean@...s.org>,
        wfg@...ux.intel.com, Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...radead.org>,
        linux-mediatek@...ts.infradead.org,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
        linux-amlogic@...ts.infradead.org,
        kernel test robot <fengguang.wu@...el.com>, LKP <lkp@...org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>
Subject: Re: [WARNING: A/V UNSCANNABLE][Merge tag 'media/v4.11-1' of git]
 ff58d005cd: BUG: unable to handle kernel NULL pointer dereference at
 0000039c

* Thomas Gleixner <tglx@...utronix.de> [170227 08:20]:
> On Mon, 27 Feb 2017, Tony Lindgren wrote:
> > * Ingo Molnar <mingo@...nel.org> [170227 07:44]:
> > > Because it's not the requirement that hurts primarily, but the resulting 
> > > non-determinism and the sporadic crashes. Which can be solved by making the race 
> > > deterministic via the debug facility.
> > > 
> > > If the IRQ handler crashed the moment it was first written by the driver author 
> > > we'd never see these problems.
> > 
> > Just in case this is PM related.. Maybe the spurious interrupt is pending
> > from earlier? This could be caused by glitches on the lines with runtime PM,
> > or a pending interrupt during suspend/resume. In that case IRQ_DISABLE_UNLAZY
> > might provide more clues if the problem goes away.
> 
> It's not PM related.  That's just silly hardware. At the moment when you
> enable some magic bit in the control register, which is required to probe
> the version, the fricking thing spits out a spurious interrupt despite the
> interrupt enable bit in the same control register being still disabled. Of
> course we cannot install an interrupt handler before having probed the
> version and setup other stuff, except we add magic 'if (!initialized)'
> crappola into the handler and lose the ability to install version dependent
> handlers afterwards.

OK and presumably no -EPROBE_DEFER happening either.

> Wonderful crap that, isn't it?

Sounds broken..

Regards,

Tony