linux-kernel - Re: NMI hardlock stacktrace deadlock [was Re: Linux 5.2-rc5]

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Message-ID: <20190625030345.dwbydi2w67mpp4zq@treble>
Date:   Mon, 24 Jun 2019 22:03:45 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Chris Wilson <chris@...is-wilson.co.uk>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: NMI hardlock stacktrace deadlock [was Re: Linux 5.2-rc5]

On Wed, Jun 19, 2019 at 01:42:53PM -0700, Linus Torvalds wrote:
> On Wed, Jun 19, 2019 at 12:19 PM Chris Wilson <chris@...is-wilson.co.uk> wrote:
> >
> > > Do you have the oops itself at all?
> >
> > An example at
> > https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_6310/fi-kbl-x1275/dmesg0.log
> > https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_6310/fi-kbl-x1275/boot0.log
> >
> > The bug causing the oops is clearly a driver problem. The rc5 fallout
> > just seems to be because of some shrinker changes affecting some object
> > reaping that were unfortunately still active. What perturbed the CI
> > team was the machine failed to panic & reboot.
> 
> Hmm. It's hard to guess at the cause of that. The oopses themselves
> don't look like they are happening in any particularly bad context, so
> all the normal reboot-on-oops etc stuff _should_ work.

Looking at the dmesg, panic_on_oops doesn't seem to be enabled: it went
through the rewind_stack_do_exit() path instead of the panic() path.  So
the system is apparently not configured to reboot on oops.

So I'd say the hang was presumably caused by a lock held by the oopsing
code.  So it looks normal to me, other than the original oops.

-- 
Josh