On June 19, 2025 5:45:05 AM EDT, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: >On Thu, Jun 19, 2025 at 05:42:31AM -0400, Steven Rostedt wrote: >> >> >> On June 19, 2025 5:32:26 AM EDT, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: >> >On Thu, Jun 19, 2025 at 05:07:10AM -0400, Steven Rostedt wrote: >> > >> >> Does #DB make in_nmi() true? If that's the case then we do need to handle that. >> > >> >Yes: #DF, #MC, #BP (int3), #DB and NMI all have in_nmi() true. >> > >> >Ignoring #DF because that's mostly game over, you can get them all >> >nested for up to 4 (you're well aware of the normal NMI recursion >> >crap). >> >> We probably can implement this with stacked counters. > >I would seriously consider dropping support for anything that can't do >cmpxchg at the width you need. That may be something we can do as it's a new feature and unlike the ftrace ring buffer, it won't be a regression not to support them. We currently care about x86-64, arm64, ppc 64 and s390. I'm assuming they all have a proper 64 bit cmpxchg. -- Steve
