From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from co9outboundpool.messaging.microsoft.com (co9ehsobe004.messaging.microsoft.com [207.46.163.27]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (Client CN "mail.global.frontbridge.com", Issuer "MSIT Machine Auth CA 2" (not verified)) by ozlabs.org (Postfix) with ESMTPS id CFDC92C007B for ; Mon, 3 Jun 2013 20:43:32 +1000 (EST) Date: Mon, 3 Jun 2013 18:43:15 +0800 From: Zhao Chenhui To: Benjamin Herrenschmidt Subject: Re: [PATCH] powerpc/sysfs: disable hotplug for the boot cpu Message-ID: <20130603104315.GA1365@localhost.localdomain> References: <1369727984-21505-1-git-send-email-chenhui.zhao@freescale.com> <1369727984-21505-2-git-send-email-chenhui.zhao@freescale.com> <1370036984.3928.144.camel@pasglop> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" In-Reply-To: <1370036984.3928.144.camel@pasglop> Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sat, Jun 01, 2013 at 07:49:44AM +1000, Benjamin Herrenschmidt wrote: > On Tue, 2013-05-28 at 15:59 +0800, Zhao Chenhui wrote: > > Some features depend on the boot cpu, for instance, hibernate/suspend. > > So disable hotplug for the boot cpu. > > Don't we have code to "move" the boot CPU around when that happens ? > > Ben. > Currently, the code in generic_cpu_disable() likes this: if (cpu == boot_cpuid) return -EBUSY; If the dying cpu is the boot cpu, it will return -EBUSY. In the subsequent error handling, cpu_notify_nofail(CPU_DOWN_FAILED) in _cpu_down() will be called. Unfortunately, some cpu notifier callbacks handled CPU_DOWN_PREPARE, but not CPU_DOWN_FAILED, such as sched_cpu_inactive(). So it will cause issues. If we set the hotpluggable for the boot cpu, we can prevent user applications from disabling the boot cpu. -Chenhui > > Signed-off-by: Zhao Chenhui > > --- > > arch/powerpc/kernel/sysfs.c | 4 +++- > > 1 files changed, 3 insertions(+), 1 deletions(-) > > > > diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c > > index e68a845..294b1c4e 100644 > > --- a/arch/powerpc/kernel/sysfs.c > > +++ b/arch/powerpc/kernel/sysfs.c > > @@ -655,8 +655,10 @@ static int __init topology_init(void) > > * CPU. For instance, the boot cpu might never be valid > > * for hotplugging. > > */ > > - if (ppc_md.cpu_die) > > + if (ppc_md.cpu_die && cpu != boot_cpuid) > > c->hotpluggable = 1; > > + else > > + c->hotpluggable = 0; > > > > if (cpu_online(cpu) || c->hotpluggable) { > > register_cpu(c, cpu); > > >