On Mon, Jun 25, 2018 at 04:25:57PM -0400, Steven Rostedt wrote: > On Mon, 25 Jun 2018 09:39:51 -0700 > Joel Fernandes <j...@joelfernandes.org> wrote: > > > For whatever its worth, I made some notes of what I understood from reading > > the code and old posts because I was sure I would otherwise forget > > everything: > > http://www.joelfernandes.org/linuxinternals/2018/06/15/rcu-dynticks.html > > Nice write up. I may point some people to this ;-) > > Anyway "complications due to nested NMIs (yes NMIs can nest!)" > > What arch allows for NMIs to nest. Because we don't let that happen on > x86, and there's code that I know of that is called by NMIs that is not > re-entrant, and can crash if we allow for NMIs to nest. For example > "in_nmi()" will not show that we are in_nmi() if we allow for nesting > of NMIs. It has a single bit that gets incremented when we enter NMI > code, and cleared when we leave it.
Last I checked with Andy Lutomirski, there are a number of things that, though not NMIs, act like NMIs and that can interrupt each others' handlers. This is on x86. Thanx, Paul