Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752018Ab2JHDAL (ORCPT ); Sun, 7 Oct 2012 23:00:11 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:3676 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751211Ab2JHDAJ (ORCPT ); Sun, 7 Oct 2012 23:00:09 -0400 X-IronPort-AV: E=Sophos;i="4.80,549,1344182400"; d="scan'208";a="5956546" From: Tang Chen To: mingo@redhat.com, peterz@infradead.org Cc: miaox@cn.fujitsu.com, wency@cn.fujitsu.com, linux-kernel@vger.kernel.org, linux-numa@vger.kernel.org, Tang Chen Subject: [PATCH] Do not use cpu_to_node() to find an offlined cpu's node. Date: Mon, 8 Oct 2012 10:59:43 +0800 Message-Id: <1349665183-11718-1-git-send-email-tangchen@cn.fujitsu.com> X-Mailer: git-send-email 1.7.10.1 X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2012/10/08 10:57:57, Serialize by Router on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2012/10/08 10:57:59, Serialize complete at 2012/10/08 10:57:59 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3016 Lines: 79 If a cpu is offline, its nid will be set to -1, and cpu_to_node(cpu) will return -1. As a result, cpumask_of_node(nid) will return NULL. In this case, find_next_bit() in for_each_cpu will get a NULL pointer and cause panic. Here is a call trace: [ 609.824017] Call Trace: [ 609.824017] [ 609.824017] [] select_fallback_rq+0x71/0x190 [ 609.824017] [] ? try_to_wake_up+0x2e/0x2f0 [ 609.824017] [] try_to_wake_up+0x2cb/0x2f0 [ 609.824017] [] ? __run_hrtimer+0x78/0x320 [ 609.824017] [] wake_up_process+0x15/0x20 [ 609.824017] [] hrtimer_wakeup+0x22/0x30 [ 609.824017] [] __run_hrtimer+0x83/0x320 [ 609.824017] [] ? update_rmtp+0x80/0x80 [ 609.824017] [] hrtimer_interrupt+0x106/0x280 [ 609.824017] [] ? sd_free_ctl_entry+0x68/0x70 [ 609.824017] [] smp_apic_timer_interrupt+0x69/0x99 [ 609.824017] [] apic_timer_interrupt+0x6f/0x80 There is a hrtimer process sleeping, whose cpu has already been offlined. When it is waken up, it tries to find another cpu to run, and get a -1 nid. As a result, cpumask_of_node(-1) returns NULL, and causes ernel panic. This patch fixes this problem by judging if the nid is -1. If nid is not -1, a cpu on the same node will be picked. Else, a online cpu on another node will be picked. Signed-off-by: Tang Chen --- kernel/sched/core.c | 24 +++++++++++++++--------- 1 files changed, 15 insertions(+), 9 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 66b36ab..e76dce9 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1263,18 +1263,24 @@ EXPORT_SYMBOL_GPL(kick_process); */ static int select_fallback_rq(int cpu, struct task_struct *p) { - const struct cpumask *nodemask = cpumask_of_node(cpu_to_node(cpu)); + int nid = cpu_to_node(cpu); + const struct cpumask *nodemask = NULL; enum { cpuset, possible, fail } state = cpuset; int dest_cpu; - /* 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; + /* If the cpu has been offlined, its nid was set to -1. */ + if (nid != -1) { + 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 (;;) { -- 1.7.1 -- 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/