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Date:   Tue, 2 Feb 2021 16:05:13 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Nikolay Borisov <nborisov@suse.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Alexei Starovoitov <ast@kernel.org>, bpf <bpf@vger.kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: kprobes broken since 0d00449c7a28 ("x86: Replace ist_enter()
 with nmi_enter()")
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On Tue, 2 Feb 2021 19:30:34 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> That does mean that kprobes are then fundamentally running from
> in_nmi(), which is what started all this.

I just thought about the fact that tracing records the context of the
function it is called in. If you set "in_nmi()" for all ftrace handlers,
then all functions will look like they are in an NMI context during tracing.

That is, the preempt count is checked to fill in the flags in the ring
buffer that denotes what context the event (in this case the function) was
called in.

-- Steve