From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E312DC0650E for ; Mon, 1 Jul 2019 14:10:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B5A9B2175B for ; Mon, 1 Jul 2019 14:10:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="IH7IK3ZX" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729430AbfGAOKv (ORCPT ); Mon, 1 Jul 2019 10:10:51 -0400 Received: from merlin.infradead.org ([205.233.59.134]:35548 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729372AbfGAOKu (ORCPT ); Mon, 1 Jul 2019 10:10:50 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=ND3leTtyQHL/47K3vzIhUCuphz+1LPNb9J1HXn7CNbc=; b=IH7IK3ZXhq0ixk2oUfkz6uCEF HMUZCXPAqlfGDvsKEmZHHboNrh9Nb5fjoc2rQasTCIIgIqOhMQASuvG7oYDlu4UG9cOI7+D9r4TU7 m+9PG09VKkxYJBFtGqCKdeudta5L6LVOh7i0wsTNzxnJEzPT5gIuQVBymXWAFygobiYnJqNmkIQuY SV7WcQBaSGGQ9Z2JcuaOdt2LBpD+0GSCEVKvq423krhlfZOPKBg65py1oYyLDhN0/AWA/IBh5yRM5 kDkH8i5VXFw2ywJ3QyMBtvG7w1isj6uEMzd/mVhkYqfmwHz1Ba03yLIQLl3M9+pKCLVedWV8hS1TU oCrBNPRng==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hhx0w-0008IZ-F8; Mon, 01 Jul 2019 14:10:39 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 25DC020963E3D; Mon, 1 Jul 2019 16:10:37 +0200 (CEST) Date: Mon, 1 Jul 2019 16:10:37 +0200 From: Peter Zijlstra To: John Ogness Cc: linux-kernel@vger.kernel.org, Petr Mladek , Sergey Senozhatsky , Steven Rostedt , Linus Torvalds , Greg Kroah-Hartman , Andrea Parri , Thomas Gleixner , Sergey Senozhatsky 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 List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.