4.2.8-ckt2 -stable review patch. If anyone has any objections, please let me know.
---8<------------------------------------------------------------
From: Michal Hocko <mhocko@xxxxxxxx>
commit 751e5f5c753e8d447bcf89f9e96b9616ac081628 upstream.
kernel test robot has reported the following crash:
BUG: unable to handle kernel NULL pointer dereference at 00000100
IP: [<c1074df6>] __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:[<c1074df6>] 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 <ying.huang@xxxxxxxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Tested-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
---
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
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