linux-kernel - Re: [PATCH bpf] bpf: fix nested bpf tracepoints with per-cpu data

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Message-ID: <20190607035528.43c0423d@oasis.local.home>
Date:   Fri, 7 Jun 2019 03:55:28 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Matt Mullins <mmullins@...com>, hall@...com,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>
Subject: Re: [PATCH bpf] bpf: fix nested bpf tracepoints with per-cpu data

On Thu, 6 Jun 2019 19:59:18 -0700
Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:

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