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
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
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------------------------------------------------------
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
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