The patch titled Subject: vmstat: allocate vmstat_wq before it is used has been added to the -mm tree. Its filename is vmstat-allocate-vmstat_wq-before-it-is-used.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/vmstat-allocate-vmstat_wq-before-it-is-used.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/vmstat-allocate-vmstat_wq-before-it-is-used.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Michal Hocko <mhocko@xxxxxxxxxx> Subject: vmstat: allocate vmstat_wq before it is used 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: [<c1074df6>] __queue_work+0x26/0x390 [<c1074df6>] __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:[<c1074df6>] 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] [<c1a381dd>] ? mutex_unlock+0xd/0x10 [ 3.897120] [<c1075221>] __queue_delayed_work+0xa1/0x160 [ 3.898530] [<c10764c6>] queue_delayed_work_on+0x36/0x60 [ 3.899790] [<c11494bd>] vmstat_shepherd+0xad/0xf0 [ 3.900899] [<c1075a7a>] process_one_work+0x1aa/0x4c0 [ 3.902093] [<c10759e2>] ? process_one_work+0x112/0x4c0 [ 3.903520] [<c10ac31e>] ? do_raw_spin_lock+0xe/0x150 [ 3.904853] [<c1075dd1>] worker_thread+0x41/0x440 [ 3.906023] [<c1075d90>] ? process_one_work+0x4c0/0x4c0 [ 3.907242] [<c107b7c0>] kthread+0xb0/0xd0 [ 3.908188] [<c1a3c651>] ret_from_kernel_thread+0x21/0x40 [ 3.909601] [<c107b710>] ? __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 <ying.huang@xxxxxxxxxxxxxxx> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> --- 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! 1 file changed, 1 insertion(+), 1 deletion(-) index 4ebc17d948cb..c54fd2924f25 100644 Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/vmstat.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -puN mm/vmstat.c~vmstat-allocate-vmstat_wq-before-it-is-used mm/vmstat.c --- a/mm/vmstat.c~vmstat-allocate-vmstat_wq-before-it-is-used +++ a/mm/vmstat.c @@ -1483,6 +1483,7 @@ static void __init start_shepherd_timer( 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); _ Patches currently in -mm which might be from mhocko@xxxxxxxxxx are vmstat-allocate-vmstat_wq-before-it-is-used.patch mm-rework-mapcount-accounting-to-enable-4k-mapping-of-thps-fix-5-fix.patch mm-oom-introduce-oom-reaper-fix.patch mm-oom-introduce-oom-reaper-fix-4.patch mm-oom-introduce-oom-reaper-fix-5.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html