linux-kernel - Re: [PATCH 1/2] watchdog: Fix output

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Date:	Sat, 19 Mar 2016 01:11:41 +0100 (CET)
From:	Jiri Kosina <jikos@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Don Zickus <dzickus@...hat.com>, linux-kernel@...r.kernel.org,
	rostedt@...dmis.org, mingo@...nel.org, tglx@...utronix.de
Subject: Re: [PATCH 1/2] watchdog: Fix output

On Fri, 18 Mar 2016, Peter Zijlstra wrote:

> > -#define pr_fmt(fmt) "NMI watchdog: " fmt
> > +#define pr_fmt(fmt) "Lockup detector: " fmt
> >  
> >  #include <linux/mm.h>
> >  #include <linux/cpu.h>
> > @@ -350,7 +350,7 @@ static void watchdog_overflow_callback(struct perf_event *event,
> >  		if (__this_cpu_read(hard_watchdog_warn) == true)
> >  			return;
> >  
> > -		pr_emerg("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
> > +		pr_emerg("Detected hard LOCKUP on cpu %d", this_cpu);
> >  		print_modules();
> >  		print_irqtrace_events(current);
> >  		if (regs)
> 
> It was Jiri who made this mess by replacing WARN(), which has a very
> distinct format, with this custom stuff.

Right, this was in 55537871e ("kernel/watchdog.c: perform all-CPU 
backtrace in case of hard lockup").

To be really honest, I don't really have 100% reliable explanation why I 
did it this way; I *think* it was because otherwise, in case WARN is 
preserved, we'll either

- have different output format for current (warning) CPU and all the 
  others (trigger_allbutself_cpu_backtrace())

or

- have duplicated backtrace for current CPU, one coming from WARN and one 
  coming from the all-cpu backtrace

> I think we should go back to the WARN() thing.

I don't really have strong opinion on this, but someone should pick the 
poison from the two options above; I tried in the mentioned commit, but 
apparently not to general satisfaction :)

Thanks,

-- 
Jiri Kosina
SUSE Labs