From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754603AbcAHKSq (ORCPT ); Fri, 8 Jan 2016 05:18:46 -0500 Received: from mail-wm0-f52.google.com ([74.125.82.52]:38341 "EHLO mail-wm0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753490AbcAHKSm (ORCPT ); Fri, 8 Jan 2016 05:18:42 -0500 From: Michal Hocko To: Linus Torvalds Cc: Andrew Morton , Arkadiusz Miskiewicz , Joonsoo Kim , Cristopher Lameter , Tejun Heo , Tetsuo Handa , lkp@01.org, LKML , Michal Hocko Subject: [PATCH] vmstat: allocate vmstat_wq before it is used Date: Fri, 8 Jan 2016 11:18:29 +0100 Message-Id: <1452248309-17930-1-git-send-email-mhocko@kernel.org> X-Mailer: git-send-email 2.6.4 In-Reply-To: <87r3hsg4io.fsf@yhuang-dev.intel.com> References: <87r3hsg4io.fsf@yhuang-dev.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Michal Hocko kernel test robot has reported the following crash: [ 3.870718] BUG: unable to handle kernel NULL pointer dereferenceNULL pointer dereference at 00000100 at 00000100 [ 3.872615] IP: [] __queue_work+0x26/0x390 [] __queue_work+0x26/0x390 [ 3.873758] *pdpt = 0000000000000000 *pde = f000ff53f000ff53 *pde = f000ff53f000ff53 [ 3.875096] Oops: 0000 [#1] PREEMPT PREEMPT SMP SMP [ 3.876130] CPU: 0 PID: 24 Comm: kworker/0:1 Not tainted 4.4.0-rc4-00139-g373ccbe #1 [ 3.878135] Workqueue: events vmstat_shepherd [ 3.879207] task: cb684600 ti: cb7ba000 task.ti: cb7ba000 [ 3.880445] EIP: 0060:[] EFLAGS: 00010046 CPU: 0 [ 3.881704] EIP is at __queue_work+0x26/0x390 [ 3.882823] EAX: 00000046 EBX: cbb37800 ECX: cbb37800 EDX: 00000000 [ 3.884457] ESI: 00000000 EDI: 00000000 EBP: cb7bbe68 ESP: cb7bbe38 [ 3.886005] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 [ 3.887229] CR0: 8005003b CR2: 00000100 CR3: 01fd5000 CR4: 000006b0 [ 3.888663] Stack: [ 3.895204] Call Trace: [ 3.895854] [] ? mutex_unlock+0xd/0x10 [ 3.897120] [] __queue_delayed_work+0xa1/0x160 [ 3.898530] [] queue_delayed_work_on+0x36/0x60 [ 3.899790] [] vmstat_shepherd+0xad/0xf0 [ 3.900899] [] process_one_work+0x1aa/0x4c0 [ 3.902093] [] ? process_one_work+0x112/0x4c0 [ 3.903520] [] ? do_raw_spin_lock+0xe/0x150 [ 3.904853] [] worker_thread+0x41/0x440 [ 3.906023] [] ? process_one_work+0x4c0/0x4c0 [ 3.907242] [] kthread+0xb0/0xd0 [ 3.908188] [] ret_from_kernel_thread+0x21/0x40 [ 3.909601] [] ? __kthread_parkme+0x80/0x80 The reason is that start_shepherd_timer schedules the shepherd work item which uses vmstat_wq (vmstat_shepherd) before setup_vmstat allocates that workqueue so if the further initialization takes more than HZ we might end up scheduling on a NULL vmstat_wq. This is really unlikely but not impossible. Fixes: 373ccbe59270 ("mm, vmstat: allow WQ concurrency to discover memory reclaim doesn't make any progress") Reported-by: kernel test robot Signed-off-by: Michal Hocko --- Hi Linus, I am not marking this for stable because I hope we can sneak it into 4.4. The patch is trivial and obvious. I am sorry about the breakage. If you prefer to postpone it to 4.5-rc1 because this is not really that critical and shouldn't happen most of the time then I will repost with stable tag added. Thanks! mm/vmstat.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/vmstat.c b/mm/vmstat.c index 4ebc17d948cb..c54fd2924f25 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1483,6 +1483,7 @@ static void __init start_shepherd_timer(void) BUG(); cpumask_copy(cpu_stat_off, cpu_online_mask); + vmstat_wq = alloc_workqueue("vmstat", WQ_FREEZABLE|WQ_MEM_RECLAIM, 0); schedule_delayed_work(&shepherd, round_jiffies_relative(sysctl_stat_interval)); } @@ -1550,7 +1551,6 @@ static int __init setup_vmstat(void) start_shepherd_timer(); cpu_notifier_register_done(); - vmstat_wq = alloc_workqueue("vmstat", WQ_FREEZABLE|WQ_MEM_RECLAIM, 0); #endif #ifdef CONFIG_PROC_FS proc_create("buddyinfo", S_IRUGO, NULL, &fragmentation_file_operations); -- 2.6.4