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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9AE97C636CC for ; Mon, 6 Feb 2023 03:12:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229536AbjBFDMJ (ORCPT ); Sun, 5 Feb 2023 22:12:09 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34358 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229522AbjBFDMJ (ORCPT ); Sun, 5 Feb 2023 22:12:09 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6BDCD1A4B7; Sun, 5 Feb 2023 19:12:08 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id E972E60C67; Mon, 6 Feb 2023 03:12:07 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5721CC433AC; Mon, 6 Feb 2023 03:12:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1675653127; bh=SEHqDj0pecZaoDvI2TxfvISMCoNXpVJslROmtkQHTl0=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=aBHWxbUE1qscXgToVSLDbDbOTBJx5ol3QAloFKF6quHuxSLDc6bLN0hEb6oLgxGmy MnLxdeRrgyeBdJ9pGDDQDN8qL5E9eF3ZREg1BlrIswbxzqSGfwNgKGkpU7eR7l/H+i Vbq9BwU/inl0wIHB7aGtD4Z3NEhanBgFaoByYV66gksXGt6rGyMFlx2u7/LVAOMEK5 3UQMP1Lhs7EYtOpLuMlrIWY7J57uJMJDeSdRPH5Gq31PiUX/XFKpgBmcKERl5TtGxs zZmDid7aciqyecTQEc01AFRGPklMTl/8Ni72awcEbNNyPoB7lSyFUULT/gnF3yjq+a QYealvajIFRZg== Received: by mail-ej1-f42.google.com with SMTP id mf7so30465661ejc.6; Sun, 05 Feb 2023 19:12:07 -0800 (PST) X-Gm-Message-State: AO0yUKXQj1OYwkzCxr8lt87Nj1nU8qdd5VU2CQpXDhxca9gqVyHqszgK HDc/+CsIh6KCcN2YsgRztMH+HIG+lrAREpPbv6k= X-Google-Smtp-Source: AK7set+C2OPIEjxuD4imJwgo/SdFRSDGqxy+aWdQoxwR9LsZ/L0xaRFmrPMBBJUVbKfwf6WwaCs9pUvWr8CjvlkkXS4= X-Received: by 2002:a17:906:8419:b0:884:c19c:7c6 with SMTP id n25-20020a170906841900b00884c19c07c6mr4724728ejx.120.1675653125517; Sun, 05 Feb 2023 19:12:05 -0800 (PST) MIME-Version: 1.0 References: <20230204022932.k24laszjs3v4bc3v@treble> In-Reply-To: <20230204022932.k24laszjs3v4bc3v@treble> From: Guo Ren Date: Mon, 6 Feb 2023 11:11:53 +0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 05/22] csky/cpu: Make sure arch_cpu_idle_dead() doesn't return To: Josh Poimboeuf Cc: linux-kernel@vger.kernel.org, jgross@suse.com, richard.henderson@linaro.org, ink@jurassic.park.msu.ru, mattst88@gmail.com, linux-alpha@vger.kernel.org, linux@armlinux.org.uk, linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, will@kernel.org, linux-csky@vger.kernel.org, linux-ia64@vger.kernel.org, chenhuacai@kernel.org, kernel@xen0n.name, loongarch@lists.linux.dev, f.fainelli@gmail.com, bcm-kernel-feedback-list@broadcom.com, tsbogend@alpha.franken.de, linux-mips@vger.kernel.org, jiaxun.yang@flygoat.com, mpe@ellerman.id.au, npiggin@gmail.com, christophe.leroy@csgroup.eu, linuxppc-dev@lists.ozlabs.org, ysato@users.sourceforge.jp, dalias@libc.org, linux-sh@vger.kernel.org, davem@davemloft.net, sparclinux@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, chris@zankel.net, jcmvbkbc@gmail.com, linux-xtensa@linux-xtensa.org, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, paulmck@kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-csky@vger.kernel.org On Sat, Feb 4, 2023 at 10:29 AM Josh Poimboeuf wrote: > > On Sat, Feb 04, 2023 at 09:12:31AM +0800, Guo Ren wrote: > > On Sat, Feb 4, 2023 at 6:05 AM Josh Poimboeuf wrote: > > > > > > arch_cpu_idle_dead() doesn't return. Make that more explicit with a > > > BUG(). > > > > > > BUG() is preferable to unreachable() because BUG() is a more explicit > > > failure mode and avoids undefined behavior like falling off the edge of > > > the function into whatever code happens to be next. > > > > > > Signed-off-by: Josh Poimboeuf > > > --- > > > arch/csky/kernel/smp.c | 2 ++ > > > 1 file changed, 2 insertions(+) > > > > > > diff --git a/arch/csky/kernel/smp.c b/arch/csky/kernel/smp.c > > > index b45d1073307f..0ec20efaf5fd 100644 > > > --- a/arch/csky/kernel/smp.c > > > +++ b/arch/csky/kernel/smp.c > > > @@ -317,5 +317,7 @@ void arch_cpu_idle_dead(void) > > > "jmpi csky_start_secondary" > > > : > > > : "r" (secondary_stack)); > > > + > > > + BUG(); > > Why not: > > diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c > > index f26ab2675f7d..1d3bf903add2 100644 > > --- a/kernel/sched/idle.c > > +++ b/kernel/sched/idle.c > > @@ -285,6 +285,7 @@ static void do_idle(void) > > tick_nohz_idle_stop_tick(); > > cpuhp_report_idle_dead(); > > arch_cpu_idle_dead(); > > + BUG(); > > Without the BUG() in csky arch_cpu_idle_dead(), the compiler will warn > about arch_cpu_idle_dead() returning, because it's marked __noreturn but > doesn't clearly return (as far as the compiler knows). > > And we want it marked __noreturn so we'll be more likely to catch such > bugs at build time. > > And as a bonus we get better code generation and clearer code semantics > which helps both humans and tooling understand the intent of the code. Thx for the clarification. Acked-by: Guo Ren > > -- > Josh -- Best Regards Guo Ren