On Mon, Jun 25, 2018 at 1:45 PM Paul E. McKenney <paul...@linux.vnet.ibm.com> wrote: > > 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. >
As a straightforward example, NMI and MCE can nest inside each other. IIRC we treat #DB somewhat NMI-ish-ly as well. --Andy > Thanx, Paul >
