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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 2FF8AC31E51 for ; Tue, 18 Jun 2019 09:41:44 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 00CE7206B7 for ; Tue, 18 Jun 2019 09:41:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="GgHdvEPv" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 00CE7206B7 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date: Message-ID:From:References:To:Subject:Reply-To:Content-ID:Content-Description :Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=HgG7g7ySGHxo+3RZgUzz/5KT1kWIWF8e0dYkPCWdjPA=; b=GgHdvEPvZMZUEY bJlM3NtUMCAxZ0pEBQOA58W4K5SDjU+ta9c6/gEk2QA/cmmu1oalTF4fhtHTiYVf5u7zE90Wr8Cz1 BzgKu0NUmXyR4/l6NHyn1rjqpAJenNZrgkWXLIbiZSbiAKpqkrPfOAIFqPbja36KTcPVKamF+XhAY ItpNNyKowt5IHlXkhvKNjRVRYJZlCzrQi0chmh3KKYAjR0N9VmXSBtiahSFhcCKRYZN/bzLe9z7TE Aiex03nm/EEyeIZQk2jCOgAU+CFmlntFF3VLM40rUA67EyKkaEQ21XItnmJmT11eqPAuLwHgGEoqS PkN5VdzAS14oO9N8EgKA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hdAcV-0001A4-Uv; Tue, 18 Jun 2019 09:41:39 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hdAcS-00019D-DJ for linux-arm-kernel@lists.infradead.org; Tue, 18 Jun 2019 09:41:37 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 186B0344; Tue, 18 Jun 2019 02:41:34 -0700 (PDT) Received: from [10.1.197.50] (e120937-lin.cambridge.arm.com [10.1.197.50]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 10AEE3F246; Tue, 18 Jun 2019 02:43:18 -0700 (PDT) Subject: Re: [PATCH] arm64: smp: fix smp_send_stop() behaviour To: Will Deacon References: <20190613122146.45459-1-cristian.marussi@arm.com> <20190617180913.GN30800@fuggles.cambridge.arm.com> From: Cristian Marussi Message-ID: Date: Tue, 18 Jun 2019 10:41:32 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190617180913.GN30800@fuggles.cambridge.arm.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190618_024136_546988_BDEE6234 X-CRM114-Status: GOOD ( 21.07 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, catalin.marinas@arm.com, james.morse@arm.com, dave.martin@arm.com, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Will Thanks for the review. On 17/06/2019 19:09, Will Deacon wrote: > [+James M] > > On Thu, Jun 13, 2019 at 01:21:46PM +0100, Cristian Marussi wrote: >> On a 2-CPUs system, when one CPU is already online if the other >> panics while starting-up, smp_send_stop() will fail to send any >> STOP message to the other already online core, resulting in a >> system still responsive and alive at the end of the panic procedure. >> This patch makes smp_send_stop() account also for the online status >> of the calling CPU while evaluating how many CPUs are effectively >> online: this way, an adequate number of STOPs is sent, so enforcing >> a proper freeze of the system at the end of panic even under the >> above conditions. >> >> Reported-by: Dave Martin >> Signed-off-by: Cristian Marussi >> --- >> >> This peculiar panic-procedure behaviour was exposed hitting a BUG() >> while running a KSFT cpu-hotplug test on a 2-core ARMv8 model. >> Such trigger-BUG() was fixed by a distinct commit already included >> in Linux 5.2-rc4 [0] >> >> [0] https://lore.kernel.org/linux-arm-kernel/1559576102-12156-1-git-send-email-Dave.Martin@arm.com/ >> --- >> arch/arm64/kernel/smp.c | 12 +++++++++--- >> 1 file changed, 9 insertions(+), 3 deletions(-) >> >> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c >> index bb4b3f07761a..c7d604427883 100644 >> --- a/arch/arm64/kernel/smp.c >> +++ b/arch/arm64/kernel/smp.c >> @@ -971,8 +971,14 @@ void tick_broadcast(const struct cpumask *mask) >> void smp_send_stop(void) >> { >> unsigned long timeout; >> + unsigned int this_cpu_online = cpu_online(smp_processor_id()); >> >> - if (num_online_cpus() > 1) { >> + /* >> + * If this CPU isn't fully online, it will not be counted in >> + * num_online_cpus(): on a 2-CPU system this situation will >> + * result in no message being sent to the other already online CPU. >> + */ >> + if (num_online_cpus() > this_cpu_online) { >> cpumask_t mask; >> >> cpumask_copy(&mask, cpu_online_mask); >> @@ -985,10 +991,10 @@ void smp_send_stop(void) >> >> /* Wait up to one second for other CPUs to stop */ >> timeout = USEC_PER_SEC; >> - while (num_online_cpus() > 1 && timeout--) >> + while (num_online_cpus() > this_cpu_online && timeout--) >> udelay(1); >> >> - if (num_online_cpus() > 1) >> + if (num_online_cpus() > this_cpu_online) >> pr_warning("SMP: failed to stop secondary CPUs %*pbl\n", >> cpumask_pr_args(cpu_online_mask)); > > Whilst this looks ok to me, I'm worried about whether or not we have this > sort of logic elsewhere. For example, do we need to fix > crash_smp_send_stop() (and possibly machine_kexec()) too? I think we certainly have such logic in crash_smp_send_stop() too at least, maybe it is just less easily exposed given the different use case of the function. This wanted to be just a fix only against the observed troubled panic, but I could extend it to cover similar issues spotted by code analysis, if deemed worth. Thanks Cristian > > Will > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel