linux-kernel - Re: Instrumentation and RCU

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Message-ID: <87d09k5aet.fsf@nanos.tec.linutronix.de>
Date:   Tue, 10 Mar 2020 19:31:38 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        paulmck <paulmck@...nel.org>,
        "Joel Fernandes\, Google" <joel@...lfernandes.org>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: Re: Instrumentation and RCU

Mathieu Desnoyers <mathieu.desnoyers@...icios.com> writes:
> ----- On Mar 10, 2020, at 12:48 PM, Thomas Gleixner tglx@...utronix.de wrote:
>> How do you "fix" that when you can't reach the tracepoint because you
>> trip over a breakpoint and then while trying to fixup that stuff you hit
>> another one?
>
> I may still be missing something, but if the fixup code (AFAIU the code performing
> the out-of-line single-stepping of the original instruction) belongs to a section
> hidden from instrumentation, it should not be an issue.

Sure, but what guarantees that on the way there is nothing which might
call into instrumentable code? Nothing, really.

That's why I want the explicit sections which can be analyzed by
tools. Humans (including me) are really bad at it was demonstrated
several times.

Thanks,

        tglx