linux-kernel - Re: [RFC PATCH v2 1/2] printk-rb: add a new printk ringbuffer implementation

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Date:   Mon, 1 Jul 2019 16:10:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [RFC PATCH v2 1/2] printk-rb: add a new printk ringbuffer
 implementation

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.