linux-kernel - Re: [patch V6 02/37] tracing/hwlat: Split ftrace_nmi

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Date:   Tue, 19 May 2020 18:23:56 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V6 02/37] tracing/hwlat: Split ftrace_nmi_enter/exit()

On Sat, 16 May 2020 01:45:49 +0200
Thomas Gleixner <tglx@...utronix.de> wrote:

> The hardware latency tracer calls into timekeeping and ends up in
> various instrumentable functions which is problematic vs. the kprobe
> handling especially the text poke machinery. It's invoked from
> nmi_enter/exit(), i.e. non-instrumentable code.
> 
> Split it into two parts:
> 
>  1) NMI counter, only invoked on nmi_enter() and noinstr safe
> 
>  2) NMI timestamping, to be invoked from instrumentable code
> 
> Move it into the rcu is watching regions of nmi_enter/exit() even
> if there is no actual RCU dependency right now but there is also
> no point in having it early.
> 
> The actual split of nmi_enter/exit() is done in a separate step.
> 
> Requested-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve