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Date:   Mon, 24 Feb 2020 11:10:50 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Joel Fernandes <joel@joelfernandes.org>
Cc:     linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
        rostedt@goodmis.org, mingo@kernel.org, gregkh@linuxfoundation.org,
        gustavo@embeddedor.com, tglx@linutronix.de, paulmck@kernel.org,
        josh@joshtriplett.org, mathieu.desnoyers@efficios.com,
        jiangshanlai@gmail.com, luto@kernel.org, tony.luck@intel.com,
        frederic@kernel.org, dan.carpenter@oracle.com, mhiramat@kernel.org
Subject: Re: [PATCH v4 01/27] lockdep: Teach lockdep about "USED" <- "IN-NMI"
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Message-ID: <20200224101050.GE14897@hirez.programming.kicks-ass.net>
References: <20200221133416.777099322@infradead.org>
 <20200221134215.090538203@infradead.org>
 <20200222030843.GA191380@google.com>
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On Fri, Feb 21, 2020 at 10:08:43PM -0500, Joel Fernandes wrote:
> On Fri, Feb 21, 2020 at 02:34:17PM +0100, Peter Zijlstra wrote:
> > nmi_enter() does lockdep_off() and hence lockdep ignores everything.
> > 
> > And NMI context makes it impossible to do full IN-NMI tracking like we
> > do IN-HARDIRQ, that could result in graph_lock recursion.
> 
> The patch makes sense to me.
> 
> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> 
> NOTE:
> Also, I was wondering if we can detect the graph_lock recursion case and
> avoid doing anything bad, that way we enable more of the lockdep
> functionality for NMI where possible. Not sure if the suggestion makes sense
> though!

Yeah, I considered playing trylock games, but figured I shouldn't make
it more complicated that it needs to be.