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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C7310C05027 for ; Sat, 4 Feb 2023 02:30:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=Co06zk/T54f01WPyjORCCw0BDzSeecB1b2ZfEZkrWaQ=; b=jPw0VuIO0r/frz 8p+eOc0PT9UwoRmt/H/19vaoP6AaZIf0APyTs1VSaZbXoUrKfljg3lW5H995dz//shGpoL3jlnRtk v9QQzOpuTZikNuKY3tMFvhdET+UulisfPqW/Tjbi2AkkAgPXPmmaGkCxoptQnJa38LZhuqjvTKNDQ 6Z0T6gEURe4o9DzapydEz+b01uv4z/LeLLb6iCNEl2fqhCA3PwBfj9e4Kk7hx33r4OpoVuhrPj/QF eP94ZZeH5L8OuzzjzZxFCRKzEq59Ga6zCU9Ju8IU4kSvzL0rHUU4vZ/y7S8KAVhQFkobt+d2fibNA 54uA4MeKqnaWZS8nlCVg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1pO8JD-004Hbq-EA; Sat, 04 Feb 2023 02:29:43 +0000 Received: from ams.source.kernel.org ([145.40.68.75]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1pO8J9-004HaH-Tc for linux-arm-kernel@lists.infradead.org; Sat, 04 Feb 2023 02:29:41 +0000 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 ams.source.kernel.org (Postfix) with ESMTPS id 34A96B82C1C; Sat, 4 Feb 2023 02:29:37 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4882FC433D2; Sat, 4 Feb 2023 02:29:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1675477775; bh=A31zSwlgRwgvDbdSE2DEbrUbqrKSeAqq7FjkMqnStZw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=sys04XZk8jqh8pRKO4mghhMIaZOJaNysJlIGALRMdUzBCxAI7G298EYXo2zlMRvSr v1L58VM1ZHs7x81UItVoBpt9wcZHmGDg5tNF+6JViYATk8zllrsyuNPci/+h9ThQNC KW//e75t+wHxZCqRUkgsCKq4iGfhZGkJ2TH63kQJ9oR+CjCAQa7/KkH2zX9Gq7ZUzT JuXMK4xLEjNS6GRz1ijKyXH/9LrhEwsou1WQe6fwvelXFDxVFZwSA9iJKcPffsY87l 1jDSihH/HYx9/w9lxJwcSwTV40QPZPI04Z41AbBuYIqH66hVf0PVr4wNkI33bF0LF/ Ts2VwRwiP4moA== Date: Fri, 3 Feb 2023 18:29:32 -0800 From: Josh Poimboeuf To: Guo Ren 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 Subject: Re: [PATCH 05/22] csky/cpu: Make sure arch_cpu_idle_dead() doesn't return Message-ID: <20230204022932.k24laszjs3v4bc3v@treble> References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230203_182940_279742_7411F3DF X-CRM114-Status: GOOD ( 19.17 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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. -- Josh _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel