On Thu, Feb 29, 2024 at 10:34:26AM -0800, Doug Anderson wrote: > Hi, > > On Wed, Feb 28, 2024 at 5:11 AM Daniel Thompson > <daniel.thomp...@linaro.org> wrote: > > > > > I'm still hoping to get some sort of feedback here. If people think > > > this is a terrible idea then I'll shut up now and leave well enough > > > alone, but it would be nice to actively decide and get the patch out > > > of limbo. > > > > I've read patch through a couple of times and was generally convinced by > > the "do what x86 does" argument. > > > > However until now I've always held my council since I wasn't familiar > > with these code paths and I figured it was OK for me to have no opinion > > because the first line of the description says that kgdb/kdb is 100% not > > involved in causing the problem ;-) . > > > > However today I also took a look at the HAVE_NMI architectures and there > > is no consensus between them about how to implement this: PowerPC uses > > NMI and most of the others use IRQ only, s390 special cases for the > > panic code path and acts differently compared to a normal SMP shutdown. > > > > <snip> > > > > However, if we talking ourselves into copying x86 then perhaps we should > > more accurately copy x86! Assuming I read the x86 code correctly then > > crash_smp_send_stop() will (mostly) go staight to NMI rather > > than trialling an IRQ first! That is not what is currently implemented > > in the patch for arm64. > > Sure, I'm happy to change the patch to work that way, though I might > wait to get some confirmation from a maintainer that they think this > idea is worth pursuing before spending more time on it.
100%. Don't respin on my account. > I don't think it would be hard to have the "crash stop" code jump > straight to NMI if that's what people want. Matching x86 here seems > reasonable, though I'd also say that my gut still says that even for > crash stop we should try to stop things cleanly before jumping to NMI. > I guess I could imagine that the code we're kexec-ing to generate the > core file might be more likely to find the hardware in a funny state > if we stopped CPUs w/ NMI vs IRQ. In terms of the "right thing to do" for kdump then reviewing the s390 might be a good idea. Unfortunately it's a bit different to the other arches and I can't offer a 95% answer about what that arch does. Daniel.
