linux-kernel - Re: printk.time causes rare kernel boot hangs

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Message-ID: <20230614145348.GB1640563@hirez.programming.kicks-ass.net>
Date:   Wed, 14 Jun 2023 16:53:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Richard W.M. Jones" <rjones@...hat.com>
Cc:     Aaron Thompson <dev@...ont.org>, linux-kernel@...r.kernel.org
Subject: Re: printk.time causes rare kernel boot hangs

On Wed, Jun 14, 2023 at 03:09:45PM +0200, Peter Zijlstra wrote:
> On Wed, Jun 14, 2023 at 02:03:48PM +0100, Richard W.M. Jones wrote:
> > On Wed, Jun 14, 2023 at 02:53:20PM +0200, Peter Zijlstra wrote:
> > > Ooooh, what qemu version do you have? There were some really dodgy
> > > reports all around self modifying code, all reported on 7.2, that seems
> > > to have gone away with 8.
> > 
> > > Now, all of them were using TCG, and I think you're using KVM.
> > 
> > I'm using qemu-system-x86-8.0.0-4.fc39.x86_64 with KVM.  The host
> > kernel is 6.4.0-0.rc5.41.fc39.x86_64.
> > 
> > > I've at least 36000 cycles and still nothing :-(, let me go try your
> > > .config.
> > 
> > I can definitely reproduce this with your config (but AMD host), so
> > that's odd.  Let me try with Intel hardware and your config.  You
> > really should see this with only a few thousands iterations.
> 
> Yeah, I'm running on some ancient ivb-ep, let me try on the alderlake. I
> don't really have AMD machines at hand :-/

Using v6.4-rc6-37-gb6dad5178cea, and 36000+ cycles on the ADL (affine to
big cores) later and nothing :-(

Clearly I'm doing something wrong.