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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 1hdAtB-0002KH-3T; Tue, 18 Jun 2019 09:58:53 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hdAt6-0002IU-6K for linux-arm-kernel@lists.infradead.org; Tue, 18 Jun 2019 09:58:52 +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 390A4344; Tue, 18 Jun 2019 02:58:47 -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 2F9DE3F246; Tue, 18 Jun 2019 03:00:32 -0700 (PDT) Subject: Re: [PATCH] arm64: smp: fix smp_send_stop() behaviour To: James Morse , Will Deacon References: <20190613122146.45459-1-cristian.marussi@arm.com> <20190617180913.GN30800@fuggles.cambridge.arm.com> From: Cristian Marussi Message-ID: <1bdde105-2784-c6b9-e6d7-91c760c3deef@arm.com> Date: Tue, 18 Jun 2019 10:58:45 +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: Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190618_025848_414774_65DB308C X-CRM114-Status: GOOD ( 20.17 ) 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, 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 James On 18/06/2019 10:36, James Morse wrote: > Hi Christian, Will, > > On 17/06/2019 19:09, Will Deacon wrote: >> 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. > > >>> 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? > > We should do the same in crash_smp_send_stop(), its possible a newly-online core triggers > kdump by calling panic() in the same way. > > machine_kexec() is called on the last surviving cpu after migrate_to_reboot_cpu() has run. > At first glance it looks like this could never happen there, but kexec re-enables > cpu-hotplug (commit 011e4b02f1da), and we can reschedule before we start moving memory > around, so I'm not convinced its immune... > > I'll look into machine_kexec() behavior in these regards. Thanks for the review ! Cristian > > Thanks, > > James > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel