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Date:   Wed, 8 Aug 2018 08:46:29 -0400
From:   Steven Rostedt <>
To:     Joel Fernandes <>
Cc:     Joel Fernandes <>,
        LKML <>,
        "Cc: Android Kernel" <>,
        Boqun Feng <>,
        Byungchul Park <>,
        Ingo Molnar <>,
        Masami Hiramatsu <>,
        Mathieu Desnoyers <>,
        Namhyung Kim <>,
        Paul McKenney <>,
        Peter Zijlstra <>,
        Thomas Glexiner <>,
        Tom Zanussi <>
Subject: Re: [PATCH v12 3/3] tracing: Centralize preemptirq tracepoints and
 unify their usage

On Tue, 7 Aug 2018 20:53:54 -0700
Joel Fernandes <> wrote:

> > When I talked to Paul few months ago about SRCU from NMI context, he
> > mentioned the per-cpu memory operations during srcu_read_lock can be
> > NMI interrupted, that's why we added that warning.  
> So I looked more closely, __srcu_read_lock on 2 different handles may
> still be doing a this_cpu_inc on the same location..
> (sp->sda->srcu_lock_count). :-(
> Paul any ideas on how to solve this?
> It does start to seem like a show stopper :-(

What's wrong with a this_cpu_inc()? It's atomic for the CPU. Although
it wont be atomic for the capture of the idx. But I also don't see
interrupts being disabled, thus an NMI is no different than any
interrupt doing the same thing, right?

-- Steve

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