On Tue, 20 Oct 2020 at 18:02, Marc Zyngier <m...@kernel.org> wrote: > > On 2020-10-20 13:25, Daniel Thompson wrote: > > On Tue, Oct 20, 2020 at 04:52:43PM +0530, Sumit Garg wrote: > > [...] > > >> So in general, IPI as a normal IRQ is still useful for debugging but > >> it can't debug a core which is stuck in deadlock with interrupts > >> disabled. > >> > >> And since we choose override default implementations for pseudo NMI > >> support, we need to be backwards compatible for platforms which don't > >> possess pseudo NMI support. > > > > Do the fallback implementations require a new IPI? The fallbacks > > could rely on existing mechanisms such as the smp_call_function > > family. > > Indeed. I'd be worried of using that mechanism for NMIs, but normal > IPIs should stick to the normal cross-call stuff.
Yes, the fallback implementations could rely on existing cross-call stuff but current framework only allows this fallback choice at compile time and to make this choice at runtime, we need additional framework changes like allowing arch_trigger_cpumask_backtrace() to return a boolean in order to switch to fallback mode, similar would be the case for kgdb. I think this should be doable but I am still not sure regarding the advantages of using existing IPI vs new IPI (which we will already use in case of pseudo NMI support) as normal IRQ. > > The jury is still out on why this is a good idea, given that it > doesn't work in the only interesting case (deadlocked CPUs). I think CPU soft-lockups (interrupts enabled) is an interesting case to debug as well. -Sumit > > M. > -- > Jazz is not dead. It just smells funny... _______________________________________________ Kgdb-bugreport mailing list Kgdb-bugreport@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kgdb-bugreport
