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 07:07:11PM +0100, Ingo Molnar wrote:
> 
> * Don Zickus <dzickus@redhat.com> wrote:
> 
> > > 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).
> 
> Say the kernel crashes on a CPU and keeps spewing new oopses, while write-holding 
> tasklist_lock.
> 
> Any other CPU that delivers a signal from IRQ context, trying to take the 
> tasklist_lock, will loop indefinitely until that crashing CPU releases the lock.
> 
> In that case the 'secondary' NMI warnings from all other CPUs (eventually every CPU 
> gets stuck in such a scenario) will start spewing NMI lockup messages.
> 
> Dunno. Maybe we should do your change - but also have an option to 'shut up' the 
> kernel after the first hard oops [not warning]. That would silence the secondary NMI 
> watchdog messages as well.

You mean inside the panic() routine? like a ratelimit?

Cheers,
Don