On Mon, May 6, 2019 at 8:22 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > But still, we need to emulate the call, which requires pushing the > return code back onto the stack. I believe that part is the part we are > struggling with. Yes. But I was looking at the ftrace parts because I didn't see the bug in the low-level x86 side, so... The x86 int3 faulting code itself looks so *trivially* simple, and it does work for the trivial test-case too. Which was what made me go "Hmm, maybe there's timing or something". But it could obviously also be that the trivial test-case is just too trivial, and doesn't involve nmi etc etc. Linus