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SubjectRe: [git pull] kgdb-light -v10
On Tue, Feb 12, 2008 at 10:11:13AM -0800, Linus Torvalds wrote:
>
>
> On Tue, 12 Feb 2008, Andi Kleen wrote:
> >
> > > - the kgdb commands should always act on the *current* CPU only
> > > - add one command that says "switch over to CPU #n" which just releases
> > > the current CPU and sends an IPI to that CPU #n (no timeouts, no
> > > synchronous waiting, no nothing - it's like a "continue", but with a
> > > "try to get the other CPU to stop"
> >
> > The problem I see here is that the kernel tends to get badly confused
> > if one CPU just stops responding. At some point someone does an global
> > IPI and that then hangs. You would need to hotunplug the CPU which
> > is theoretically possible, but quite intrusive.
>
> You're thinking about this totally *wrong*.
>
> You definitely do not want to hot-unplug or isolate anything at all.

I agree that it wouldn't be a good idea -- i was just pointing out
consequences of your proposal.

> Just let the other CPU's hang naturally if they need to wait for IPI's
> etc. What's the downside?

There tend to be timeouts (e.g. softlock/nmi watchdog at least). I think
some of the IPIs eventually time out too. In general losing a lot
of time can lead to weird side effects.

-Andi


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