Re: [debug patch] printk: Add a printk killswitch to robustify NMIwatchdog messages

[Arne Jansen]

On 05.06.2011 13:36, Ingo Molnar wrote:
> * Ingo Molnar<mingo@xxxxxxx>  wrote:
>
> > > If the ticks stop this suggests a lockup within the printk code.
> > > [...]
> >
> > In which case the printk-killswitch patch below (to be applied
> > *instead* of the previous debugging patch i sent) should provide
> > the desired NMI watchdog output on the serial console.
> >
> > Warning: it's entirely untested.

How is the output supposed to come through? shouldn't printk revert
to early_printk instead of just returning?


> Note, since this is an SMP box, if the lockup messages show up with
> this patch but are mixed up with each other then adding a spinlock
> around the WARN() would probably help keeping the output serialized.
>
> A simple:
>
>   static DEFINE_SPINLOCK(watchdog_output_lock);
>
>   ...
> 	spin_lock(&watchdog_output_lock);
>   ...
> 	[ the WARN_ON() logic. ]
>   ...
> 	spin_unlock(&watchdog_output_lock);
>   ...
>
> would suffice.
>
> Thanks,
>
> 	Ingo
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