linux-kernel - Re: [PATCH v3 09/22] sched,rcu,tracing: Avoid tracing before in

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Message-ID: <20200219105034.40915c50@gandalf.local.home>
Date:   Wed, 19 Feb 2020 10:50:34 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        mingo@...nel.org, joel@...lfernandes.org,
        gregkh@...uxfoundation.org, gustavo@...eddedor.com,
        tglx@...utronix.de, paulmck@...nel.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        luto@...nel.org, tony.luck@...el.com, frederic@...nel.org,
        dan.carpenter@...cle.com, mhiramat@...nel.org,
        "Steven Rostedt (VMware)" <rosted@...dmis.org>
Subject: Re: [PATCH v3 09/22] sched,rcu,tracing: Avoid tracing before
 in_nmi() is correct

On Wed, 19 Feb 2020 15:47:33 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> If we call into a tracer before in_nmi() becomes true, the tracer can
> no longer detect it is called from NMI context and behave correctly.
> 
> Therefore change nmi_{enter,exit}() to use __preempt_count_{add,sub}()
> as the normal preempt_count_{add,sub}() have a (desired) function
> trace entry.
> 
> This fixes a potential issue with current code; AFAICT when the
> function-tracer has stack-tracing enabled __trace_stack() will
> malfunction when it hits the preempt_count_add() function entry from
> NMI context.
> 
> Suggested-by: Steven Rostedt (VMware) <rosted@...dmis.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>

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


-- Steve