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Date:   Fri, 7 Jun 2019 03:55:28 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc:     Matt Mullins <mmullins@fb.com>, hall@fb.com,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        bpf <bpf@vger.kernel.org>, Networking <netdev@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>
Subject: Re: [PATCH bpf] bpf: fix nested bpf tracepoints with per-cpu data
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On Thu, 6 Jun 2019 19:59:18 -0700
Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:

> On Thu, Jun 6, 2019 at 1:17 PM Matt Mullins <mmullins@fb.com> wrote:
> >
> > 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