Re: [PATCH v3] watchdog: touch_nmi_watchdog should only touch local cpu not every one

[Don Zickus <dzickus@redhat.com>]

On Wed, Nov 10, 2010 at 08:49:41AM +0100, Ingo Molnar wrote:
> 
> * Don Zickus <dzickus@redhat.com> wrote:
> 
> > I ran into a scenario where while one cpu was stuck and should have panic'd 
> > because of the NMI watchdog, it didn't.  The reason was another cpu was spewing 
> > stack dumps on to the console.  Upon investigation, I noticed that when writing to 
> > the console and also when dumping the stack, the watchdog is touched.
> > 
> > This causes all the cpus to reset their NMI watchdog flags and the 'stuck' cpu 
> > just spins forever.
> 
> Hm, the flip side is that if a CPU is stuck spewing backtraces, we will now make all 
> the other CPUs a lot more noisy - which might only 'lock up' because this CPU is 
> stuck spewing oopses, right?

When you say the other CPUs will be a lot more noisy, is that because they
are busy processing backtraces for the first cpu to spew?  I guess I don't
understand how the other CPUs could have their interrupts off the whole
time while the first cpu is spewing a backtrace (just trying to educate
myself).

Cheers,
Don