Re: [PATCH v4] panic: Avoid the extra noise dmesg

[Kees Cook]

On Mon, Dec 10, 2018 at 10:17 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> On Fri,  7 Dec 2018 17:51:19 +0800
> Feng Tang <feng.tang@xxxxxxxxx> wrote:
>
> > When kernel panic happens, it will first print the panic call stack,
> > then the ending msg like:
> >
> > [   35.743249] ---[ end Kernel panic - not syncing: Fatal exception
> > [   35.749975] ------------[ cut here ]------------
> >
> > The above message are very useful for debugging.
> >
> > But if system is configured to not reboot on panic, say the "panic_timeout"
> > parameter equals 0, it will likely print out many noisy message like
> > WARN() call stack for each and every CPU except the panic one, messages
> > like below:
>
>
> > Keeping the interrupt disabled will avoid the noisy message.
> >
> > When code runs to this point, it means user has chosed to not reboot, or
> > do any special handling by using the panic notifier method, the only reason
> > to enable the interrupt may be sysrq migic key and panic_blink function
> > (though may not work even with irq enabled).
> >
> > So make the irq disabled by default and add a cmdline parameter
> > "panic_keep_irq_on" to turn it on when needed.
> >
> > Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
> >
>
> Acked-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>

I'm fine with the new boot param, but I think we need to leave it how
it was by default: systems that want to see the blinking aren't going
to have a screen to read about what boot param they need to add.
Currently, we'll blink and spew extra warnings. With this patch we'll
not blink and not spew: a headless machine will have no indication
that a panic happened.

-Kees

--
Kees Cook