From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleg Nesterov Subject: Re: [RFC PATCH v3 7/9] yield_to(), cpu-hotplug: Prevent offlining of other CPUs properly Date: Sun, 9 Dec 2012 20:48:26 +0100 Message-ID: <20121209194826.GB2816@redhat.com> References: <20121207173702.27305.1486.stgit@srivatsabhat.in.ibm.com> <20121207173950.27305.39499.stgit@srivatsabhat.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mx1.redhat.com ([209.132.183.28]:3895 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758871Ab2LITsZ (ORCPT ); Sun, 9 Dec 2012 14:48:25 -0500 Content-Disposition: inline In-Reply-To: <20121207173950.27305.39499.stgit@srivatsabhat.in.ibm.com> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: "Srivatsa S. Bhat" Cc: tglx@linutronix.de, peterz@infradead.org, paulmck@linux.vnet.ibm.com, rusty@rustcorp.com.au, mingo@kernel.org, akpm@linux-foundation.org, namhyung@kernel.org, vincent.guittot@linaro.org, tj@kernel.org, sbw@mit.edu, amit.kucheria@linaro.org, rostedt@goodmis.org, rjw@sisk.pl, wangyun@linux.vnet.ibm.com, xiaoguangrong@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org On 12/07, Srivatsa S. Bhat wrote: > > Once stop_machine() is gone from the CPU offline path, we won't be able to > depend on local_irq_save() to prevent CPUs from going offline from under us. OK, I guess we need to avoid resched_task()->smp_send_reschedule() after __cpu_disable() and before migrate_tasks(). But, whatever problem we have, > Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going offline, > while invoking from atomic context. it should be solved, so... > - if (preempt && rq != p_rq) > + if (preempt && rq != p_rq && cpu_online(task_cpu(p))) Why do we need this change? Afaics, you could add BUG_ON(!cpu_online(...)) instead? I am just curious. Oleg.