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 2B89DC61DA4 for ; Tue, 14 Feb 2023 18:23:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229996AbjBNSXb (ORCPT ); Tue, 14 Feb 2023 13:23:31 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52410 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232171AbjBNSX2 (ORCPT ); Tue, 14 Feb 2023 13:23:28 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 06E342BF04; Tue, 14 Feb 2023 10:23:26 -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 81FDB6181E; Tue, 14 Feb 2023 18:23:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3376FC433EF; Tue, 14 Feb 2023 18:23:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1676399005; bh=6EEHFrLsabjvymp2QY0maJnB4Ezo1N96TizvWsxliSs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ewo4sNIkf4SKN8X81e1VZLV0gftWY9x5Idojfu6eT2b5ZqWCugH7cdipfgrW/yItW dqagFjGOxb/3bL82FQa8uuxe//ztDAd9OjP7hBFIDi33dsqHZZjtip3V1HJ2oMssgq JOC+Yor+xpMwuL0MvLKpSDnAPlafCWbIbj+fVaPjRgLXxBLYj2+reObJ0duhgkj1On B/RwdybgTkIi3ajOUQ2j7ORpSeUDMZz187rZ02sRoCPqHerIGi+6Ive3pLH2MHMcC/ Wt6l7B+BR9KKMKD4veoKROyWZ38VxJ/Bk61QLyW3eGZbXyZkY95I+3EgwPU2h+98Tw pND7dbVAeFWAA== Date: Tue, 14 Feb 2023 10:23:22 -0800 From: Josh Poimboeuf To: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= 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, guoren@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 v2 19/24] xtensa/cpu: Make sure cpu_die() doesn't return Message-ID: <20230214182322.r5tyeowxzloiuh72@treble> References: <1b4afd82-83cb-0060-7cab-8e16d2e69ff9@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1b4afd82-83cb-0060-7cab-8e16d2e69ff9@linaro.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 14, 2023 at 08:55:32AM +0100, Philippe Mathieu-Daudé wrote: > Hi Josh, > > On 14/2/23 08:05, Josh Poimboeuf wrote: > > cpu_die() 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/xtensa/kernel/smp.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/arch/xtensa/kernel/smp.c b/arch/xtensa/kernel/smp.c > > index 4dc109dd6214..7bad78495536 100644 > > --- a/arch/xtensa/kernel/smp.c > > +++ b/arch/xtensa/kernel/smp.c > > Can you update the documentation along? Currently we have: > > /* > * Called from the idle thread for the CPU which has been shutdown. > * > * Note that we disable IRQs here, but do not re-enable them > * before returning to the caller. This is also the behaviour > * of the other hotplug-cpu capable cores, so presumably coming > * out of idle fixes this. > */ void __ref cpu_die(void) { idle_task_exit(); local_irq_disable(); __asm__ __volatile__( " movi a2, cpu_restart\n" " jx a2\n"); BUG(); } Hm, not only is the comment wrong, but it seems to be branching to cpu_restart? That doesn't seem right at all. Max/Chris? -- Josh