linux-kernel - Re: commit 3d5bfbd97163 versus -rt

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Date:   Tue, 15 Jun 2021 13:09:59 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        linux-rt-users@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Esben Haabendal <esben@...nix.com>
Subject: Re: commit 3d5bfbd97163 versus -rt

On Tue, 15 Jun 2021 18:24:20 +0200
Rasmus Villemoes <rasmus.villemoes@...vas.dk> wrote:

> > ~ # uname -r
> > 5.10.42-00001-g10216cf63a12
> > ~ # grep -ow threadirqs /proc/cmdline
> > threadirqs
> > ~ # zcat /proc/config.gz | grep FORCED_THREADING
> > CONFIG_IRQ_FORCED_THREADING=y
> > ~ # dmesg | grep WARNING
> > ~ #  
> 
> And as an extra data point, it also doesn't trigger on 5.10.41-rt42
> configured without PREEMPT_RT but with threadirqs on the command line.

Sounds to me that there's a "spin_lock_irq*" somewhere in the path, because
from what I can see, there's not much difference with the IRQ code between
5.10.41 and 5.10.41-rt42. But if you are seeing it only with PREEMPT_RT
set, that tells me that without PREEMPT_RT, interrupts are disabled at that
point, but not with PREEMPT_RT. The only thing I can think of that would do
that is a spin_lock_irq*() taken (not a raw_spin_lock_irq*()).

-- Steve