From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tang Chen Subject: Re: [PATCH] Do not use cpu_to_node() to find an offlined cpu's node. Date: Tue, 09 Oct 2012 16:39:27 +0800 Message-ID: <5073E2BF.9050306@cn.fujitsu.com> References: <1349665183-11718-1-git-send-email-tangchen@cn.fujitsu.com> <5073E18A.2090203@cn.fujitsu.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5073E18A.2090203@cn.fujitsu.com> Sender: linux-numa-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Wen Congyang , David Rientjes Cc: mingo@redhat.com, peterz@infradead.org, miaox@cn.fujitsu.com, linux-kernel@vger.kernel.org, linux-numa@vger.kernel.org Hi David, Thanks for reviewing this patch. :) On 10/09/2012 04:34 PM, Wen Congyang wrote: > At 10/09/2012 02:21 PM, David Rientjes Wrote: >> On Mon, 8 Oct 2012, Tang Chen wrote: >>> + /* If the cpu has been offlined, its nid was set to -1. */ >>> + if (nid != -1) { >> >> NUMA_NO_NODE. Yes, NUMA_NO_NODE is better. I'll improve it, thanks. :) >> >> Eek, the nid shouldn't be -1 yet, though, for cpu hotplug since this >> should be called at CPU_DYING level and migrate_tasks() still sees a valid >> cpu. As Wen said below, nid is now set to -1 when cpu is hotremoved. I reproduce this problem in this situation: all cpus are online, and hot remove a system board directorily, without offlining any cpu. As a result, the removed cpu's nid is set to -1, and this causes problems. > > the cpu's node is set when the cpu is hotpluged(not online), and it will > be cleared when the cpu is hotremoved(This patch is in akpm tree): > https://lkml.org/lkml/2012/9/3/39 > > I guess the task is in sleep state when the cpu is offlined, and it doesn't > be migrated to another cpu. > > Thanks > Wen Congyang > >> >> On x86, cpumask_of_node() is always guaranteed to return a valid cpumask >> after boot so presumably this is a problem in some non-x86 arch code and >> isn't actually a sched problem. BTW, my box is x86. I think for the reason I said above, cpumask_of_node() will no longer guaranteed anything even if on x86. Thanks. :) >> >>> + nodemask = cpumask_of_node(nid); >>> + >>> + /* Look for allowed, online CPU in same node. */ >>> + for_each_cpu(dest_cpu, nodemask) { >>> + if (!cpu_online(dest_cpu)) >>> + continue; >>> + if (!cpu_active(dest_cpu)) >>> + continue; >>> + if (cpumask_test_cpu(dest_cpu, tsk_cpus_allowed(p))) >>> + return dest_cpu; >>> + } >>> } >>> >>> for (;;) { >> > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >