From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Michal Hocko , Andrew Morton , Linus Torvalds , Kamal Mostafa Subject: [PATCH 4.2.y-ckt 298/305] vmstat: allocate vmstat_wq before it is used Date: Fri, 15 Jan 2016 16:01:52 -0800 Message-Id: <1452902519-2754-299-git-send-email-kamal@canonical.com> In-Reply-To: <1452902519-2754-1-git-send-email-kamal@canonical.com> References: <1452902519-2754-1-git-send-email-kamal@canonical.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: 4.2.8-ckt2 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: Michal Hocko commit 751e5f5c753e8d447bcf89f9e96b9616ac081628 upstream. kernel test robot has reported the following crash: BUG: unable to handle kernel NULL pointer dereference at 00000100 IP: [] __queue_work+0x26/0x390 *pdpt = 0000000000000000 *pde = f000ff53f000ff53 *pde = f000ff53f000ff53 Oops: 0000 [#1] PREEMPT PREEMPT SMP SMP CPU: 0 PID: 24 Comm: kworker/0:1 Not tainted 4.4.0-rc4-00139-g373ccbe #1 Workqueue: events vmstat_shepherd task: cb684600 ti: cb7ba000 task.ti: cb7ba000 EIP: 0060:[] EFLAGS: 00010046 CPU: 0 EIP is at __queue_work+0x26/0x390 EAX: 00000046 EBX: cbb37800 ECX: cbb37800 EDX: 00000000 ESI: 00000000 EDI: 00000000 EBP: cb7bbe68 ESP: cb7bbe38 DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 CR0: 8005003b CR2: 00000100 CR3: 01fd5000 CR4: 000006b0 Stack: Call Trace: __queue_delayed_work+0xa1/0x160 queue_delayed_work_on+0x36/0x60 vmstat_shepherd+0xad/0xf0 process_one_work+0x1aa/0x4c0 worker_thread+0x41/0x440 kthread+0xb0/0xd0 ret_from_kernel_thread+0x21/0x40 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 Tested-by: Tetsuo Handa Cc: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Kamal Mostafa --- mm/vmstat.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/vmstat.c b/mm/vmstat.c index a94a02a..705d4a1 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1461,6 +1461,7 @@ 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)); } @@ -1528,7 +1529,6 @@ 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); -- 1.9.1