Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935057AbcJUPLt (ORCPT ); Fri, 21 Oct 2016 11:11:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60316 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932934AbcJUPLq (ORCPT ); Fri, 21 Oct 2016 11:11:46 -0400 Date: Fri, 21 Oct 2016 11:11:14 -0400 From: Don Zickus To: Andrew Morton Cc: Babu Moger , mingo@kernel.org, ak@linux.intel.com, jkosina@suse.cz, baiyaowei@cmss.chinamobile.com, atomlin@redhat.com, uobergfe@redhat.com, tj@kernel.org, hidehiro.kawai.ez@hitachi.com, johunt@akamai.com, davem@davemloft.net, sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org, sam@ravnborg.org Subject: Re: [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and arch_watchdog_nmi_disable Message-ID: <20161021151114.GC35881@redhat.com> References: <1476391082-77928-1-git-send-email-babu.moger@oracle.com> <1476391082-77928-2-git-send-email-babu.moger@oracle.com> <20161019170012.6006d06d9326e62a8059fd08@linux-foundation.org> <20161020161414.GE35881@redhat.com> <20161020202527.b01839356c6d34ed0cba3569@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161020202527.b01839356c6d34ed0cba3569@linux-foundation.org> User-Agent: Mutt/1.5.23.1 (2014-03-12) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Fri, 21 Oct 2016 15:11:45 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2260 Lines: 57 On Thu, Oct 20, 2016 at 08:25:27PM -0700, Andrew Morton wrote: > On Thu, 20 Oct 2016 12:14:14 -0400 Don Zickus wrote: > > > > > -static int watchdog_nmi_enable(unsigned int cpu) { return 0; } > > > > -static void watchdog_nmi_disable(unsigned int cpu) { return; } > > > > +/* > > > > + * These two functions are mostly architecture specific > > > > + * defining them as weak here. > > > > + */ > > > > +int __weak arch_watchdog_nmi_enable(unsigned int cpu) { return 0; } > > > > +void __weak arch_watchdog_nmi_disable(unsigned int cpu) { return; } > > > > + > > > > #endif /* CONFIG_HARDLOCKUP_DETECTOR */ > > > > > > This is a strange way of using __weak. > > > > > > Take a look at (one of many examples) kernel/module.c:module_alloc(). > > > We simply provide a default implementation and some other compilation > > > unit can override (actually replace) that at link time. No strange > > > ifdeffing needed. > > > > Yeah, this is mostly because of how we enable the hardlockup detector. > > > > Some arches use the perf hw and enable CONFIG_HARDLOCKUP_DETECTOR. Other > > arches just use their own variant of nmi and set CONFIG_HAVE_NMI_WATCHDOG and > > the rest of the arches do not use this. > > > > So the thought was if CONFIG_HARDLOCKUP_DETECTOR use that implementation, > > everyone else use the __weak version. Then the arches like sparc can override > > the weak version with their own nmi enablement. > > > > I don't know how to represent those 3 states correctly and the above is what > > we end up with. > > > > Is there a suitable site where we could capture these considerations in > a code comment? Hi Andrew, I am not sure I understand your question. When you say 'site', are you referring to the kernel/watchdog.c file? The other approach that might help de-clutter this file, is to pull out the HARDLOCKUP_DETECTOR changes (as they are arch specific) and move it to say kernel/watchdog_hw_ld.c. Then all the nmi hooks in kernel/watchdog.c can be __weak and overridden by the kernel_watchdog_hw_ld.c file or the sparc files. This would leave kernel/watchdog.c with just a framework and the arch-agnostic softlockup detector. Probably easier to read and digest. Thoughts? Cheers, Don