On Thu, 6 Jun 2019 19:59:18 -0700
Andrii Nakryiko [off-list ref] wrote:

On Thu, Jun 6, 2019 at 1:17 PM Matt Mullins [off-list ref] wrote:

quoted

BPF_PROG_TYPE_RAW_TRACEPOINTs can be executed nested on the same CPU, as
they do not increment bpf_prog_active while executing.

This enables three levels of nesting, to support
  - a kprobe or raw tp or perf event,
  - another one of the above that irq context happens to call, and
  - another one in nmi context  

Can NMIs be nested?

No, otherwise several things in the kernel will break.

-- Steve