Re: RT kernel v4.14 NULL pointer dereferences

From: Roosen Henri <Henri.Roosen@ginzinger.com>
To: "bigeasy@linutronix.de" <bigeasy@linutronix.de>
Cc: "linux-rt-users@vger.kernel.org" <linux-rt-users@vger.kernel.org>,
	"williams@redhat.com" <williams@redhat.com>
Subject: Re: RT kernel v4.14 NULL pointer dereferences
Date: Mon, 17 Aug 2020 08:12:31 +0000	[thread overview]
Message-ID: <25412beffb96ab8c2b8f869bdac5a66c49faa5ca.camel@ginzinger.com> (raw)
In-Reply-To: <20200814115848.w4m2bfqttkid6woi@linutronix.de>

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Henri Roosen | Entwicklung Software

GINZINGER ELECTRONIC SYSTEMS GMBH

Tel.: +43 7723 5422 161
Mail: henri.roosen@ginzinger.com
Web: www.ginzinger.com

On Fri, 2020-08-14 at 13:58 +0200, Sebastian Andrzej Siewior wrote:
> On 2020-06-16 07:30:33 [+0000], Roosen Henri wrote:
> > Hi RT-experts,
> >
> > Duration tests with RT enabled v4.14 kernels on our ARM iMX6Q
> > systems
> > are showing "Unable to handle kernel NULL pointer dereference at
> > virtual address" after running for some months. The same tests on
> > NON-
> > RT kernels don't show any problem and have been running without any
> > problems for more than 20 months now.
> >
> > I've been updating the tests from time to time with more recent
> > kernels. Testing is basically done with cyclictest, in parallel
> > with
> > some load scripts/hackbench. Please have a look at the kernel
> > traces:
> > 4.14.71-rt44  -> https://paste.debian.net/1152206/
> > 4.14.106-rt56 -> https://paste.debian.net/1152204/
> > 4.14.146-rt67 -> https://paste.debian.net/1152202/
> >
> > I've seen the v4.14-rt branch got some fixes, so my questions are:
> > 1) is problem I'm facing known and fixed in v4.14-rt, or
> > 2) is the problem I'm seeing a new issue probably still unfixed in
> > 4.14.183-rt83 (which I'm testing right now)?
> >
> > Any help is highly appreciated!
>
> So this has not fixed all by itself?
> Is the 4.14 series the only one that is affected?

No, unfortunately not.

I ended up testing the v4.14.184-rt84 on two systems and the v5.4.45-
rt27 on another system, all iMX6Q. Only one of the v4.14 systems is
still running, the other v4.14 system dumping backtraces until
eventually reset, the v5.4 system endlessly dumping backtraces:

v4.14: https://paste.ubuntu.com/p/ZdFYhs4pjx/
v5.4: https://paste.ubuntu.com/p/wZPCQv8KjX/

If the backtraces don't point to a root-cause, are there any kernel
configuration options which are usefull to track this issue down?

Thanks!

>
> > Thanks,
> > Henri
>
> Sebastian

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