linux-kernel - Re: [PATCH v3 01/22] hardirq/nmi: Allow nested nmi

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Message-ID: <20200219170725.GO18400@hirez.programming.kicks-ass.net>
Date:   Wed, 19 Feb 2020 18:07:25 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Steven Rostedt <rostedt@...dmis.org>, 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,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH v3 01/22] hardirq/nmi: Allow nested nmi_enter()

On Wed, Feb 19, 2020 at 05:56:50PM +0100, Borislav Petkov wrote:
> On Wed, Feb 19, 2020 at 10:31:26AM -0500, Steven Rostedt wrote:
> > Probably should document somewhere (in a comment above nmi_enter()?)
> > that we allow nmi_enter() to nest up to 15 times.
> 
> Yah, and can we make the BUG_ON() WARN_ON or so instead, so that there's
> at least a chance to be able to catch it for debugging. Or is the box
> going to be irreparably wedged after the 4 bits overflow?

It's going to be fairly buggered, because at that point in_nmi() is
going to be false again. It might survive for a little, it might not.