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=-7.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 ED81CC5519F for ; Wed, 18 Nov 2020 15:50:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 877DE247AF for ; Wed, 18 Nov 2020 15:50:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="eUx4eYF2" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727679AbgKRPt6 (ORCPT ); Wed, 18 Nov 2020 10:49:58 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:32076 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726211AbgKRPt6 (ORCPT ); Wed, 18 Nov 2020 10:49:58 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1605714596; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=MQ3atbt49o/FeEWNxZ+RfU8ToGXg/yRCCUXrGgUjXe4=; b=eUx4eYF2CIPcR4/HxCE9CPgfcbgZuwdOnCkQoB6GdmZmY95FUpj1UVaUB9ZHpur9uhoKVV DROTfrby3vflpfNbzT8fnomoxx4AK6bF1M5+1swXsWOhS94I5GkXj/ioaMAjwFdics5h0o BzftRAGgLSiSWAeEgaMP2XlpeGwGWyw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-542-_VdeTqYPOoqSMsJBHrnhAg-1; Wed, 18 Nov 2020 10:49:54 -0500 X-MC-Unique: _VdeTqYPOoqSMsJBHrnhAg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 39860873114; Wed, 18 Nov 2020 15:49:53 +0000 (UTC) Received: from localhost (unknown [10.18.25.174]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5DE655D9D2; Wed, 18 Nov 2020 15:49:45 +0000 (UTC) Date: Wed, 18 Nov 2020 10:49:44 -0500 From: Mike Snitzer To: Randy Dunlap Cc: Christian Borntraeger , linux-kernel@vger.kernel.org, Mikulas Patocka , Alasdair Kergon , dm-devel@redhat.com, Heiko Carstens , Vasily Gorbik , linux-s390@vger.kernel.org Subject: Re: md: dm-writeback: add __noreturn to BUG-ging function Message-ID: <20201118154944.GB545@redhat.com> References: <20201113225228.20563-1-rdunlap@infradead.org> <344abf76-9405-58ba-2dc4-27cab88c974d@de.ibm.com> <20201117163147.GA27243@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201117163147.GA27243@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 17 2020 at 11:31am -0500, Mike Snitzer wrote: > On Mon, Nov 16 2020 at 6:00pm -0500, > Randy Dunlap wrote: > > > On 11/15/20 11:30 PM, Christian Borntraeger wrote: > > > > > > > > > On 13.11.20 23:52, Randy Dunlap wrote: > > >> Building on arch/s390/ flags this as an error, so add the > > >> __noreturn attribute modifier to prevent the build error. > > >> > > >> cc1: some warnings being treated as errors > > >> ../drivers/md/dm-writecache.c: In function 'persistent_memory_claim': > > >> ../drivers/md/dm-writecache.c:323:1: error: no return statement in function returning non-void [-Werror=return-type] > > > > > > ok with me, but I am asking why > > > > > > the unreachable macro is not good enough. For x86 it obviously is. > > > > > > form arch/s390/include/asm/bug.h > > > #define BUG() do { \ > > > __EMIT_BUG(0); \ > > > unreachable(); \ > > > } while (0) > > > > > > > Hi Christian, > > > > Good question. > > I don't see any guidance about when to use one or the other etc. > > > > I see __noreturn being used 109 times and unreachable(); > > being used 33 times, but only now that I look at them. > > That had nothing to do with why I used __noreturn in the patch. > > But doesn't that speak to the proper fix being needed in unreachable()? > Or at a minimum the fix is needed to arch/s390/include/asm/bug.h's BUG. > > I really don't think we should be papering over that by sprinkling > __noreturn around the kernel's BUG() callers. > > Maybe switch arch/s390/include/asm/bug.h's BUG to be like > arch/mips/include/asm/bug.h? It itself uses __noreturn with a 'static > inline' function definition rather than #define. > > Does that fix the issue? > > Thanks, > Mike > > p.s. you modified dm-writecache.c (not dm-writeback, wich doesn't > exist). I don't think my suggestion will help.. given it'd still leave persistent_memory_claim() without a return statement. Think it worthwhile to just add a dummy 'return 0;' after the BUG(). Mike