From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 9B24C2C008C for ; Wed, 12 Jun 2013 13:25:30 +1000 (EST) Message-ID: <1371007522.8250.169.camel@pasglop> Subject: Re: [PATCH] powerpc/sysfs: disable hotplug for the boot cpu From: Benjamin Herrenschmidt To: Zhao Chenhui Date: Wed, 12 Jun 2013 13:25:22 +1000 In-Reply-To: <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> <20130603104315.GA1365@localhost.localdomain> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 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 Mon, 2013-06-03 at 18:43 +0800, Zhao Chenhui wrote: > 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; But the code in pseries/hotplug-cpu.c doesn't, we just "move" the boot CPU around when that happens. Any reason we can't do that generically ? Cheers, Ben. > 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); > > > > > >