On Sat, Sep 23, 2017 at 1:56 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > + > + /* Page faults can happen in NMI handlers, so check... */ > + if (READ_ONCE(rdtp->dynticks_nmi_nesting)) > + return; > + What is the reason for the READ_ONCE() here (and in the other case)? It doesn't seem to have any actual reason. It's a "stable" per-cpu value in that even if an NMI were to happen, it gets incremented and then decremented, so there is nothing really volatile about it anywhere that I can see. So the READ_ONCE() seems to be just pure confusion. What am I missing? Linus