Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 1 Jul 2019 16:10:37 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     John Ogness <john.ogness@linutronix.de>
Cc:     linux-kernel@vger.kernel.org, Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrea Parri <andrea.parri@amarulasolutions.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: [RFC PATCH v2 1/2] printk-rb: add a new printk ringbuffer
 implementation
Message-ID: <20190701141037.GY3402@hirez.programming.kicks-ass.net>
References: <20190607162349.18199-1-john.ogness@linutronix.de>
 <20190607162349.18199-2-john.ogness@linutronix.de>
 <20190618114747.GQ3436@hirez.programming.kicks-ass.net>
 <87k1df28x4.fsf@linutronix.de>
 <20190626224034.GK2490@worktop.programming.kicks-ass.net>
 <87mui2ujh2.fsf@linutronix.de>
 <20190628154435.GZ7905@worktop.programming.kicks-ass.net>
 <877e92f388.fsf@linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <877e92f388.fsf@linutronix.de>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Jul 01, 2019 at 12:39:35PM +0200, John Ogness wrote:

> Thanks. I overlooked that subtle detail. Can I assume NMIs do not exist
> on architectures that need to implement locking for cmpxchg()? Or did I
> just hit a major obstacle?

I think that is a fair assumption, I'm not aware of anybody having NMIs
_and_ 'broken' atomics.

Then again, we also have ARCH_HAVE_NMI_SAFE_CMPXCHG.