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Date:	Mon, 7 Jul 2014 10:20:11 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
CC:	<tj@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] workqueue: initialize cpumask of wq_numa_possible_cpumask

(2014/07/07 10:04), Lai Jiangshan wrote:
> On 07/07/2014 08:33 AM, Yasuaki Ishimatsu wrote:
>> (2014/07/07 9:19), Lai Jiangshan wrote:
>>> On 07/07/2014 01:21 AM, Yasuaki Ishimatsu wrote:
>>>> When hot-adding and onlining CPU, kernel panic occurs, showing following
>>>> call trace.
>>>>
>>>>    BUG: unable to handle kernel paging request at 0000000000001d08
>>>>    IP: [<ffffffff8114acfd>] __alloc_pages_nodemask+0x9d/0xb10
>>>>    PGD 0
>>>>    Oops: 0000 [#1] SMP
>>>>    ...
>>>>    Call Trace:
>>>>     [<ffffffff812b8745>] ? cpumask_next_and+0x35/0x50
>>>>     [<ffffffff810a3283>] ? find_busiest_group+0x113/0x8f0
>>>>     [<ffffffff81193bc9>] ? deactivate_slab+0x349/0x3c0
>>>>     [<ffffffff811926f1>] new_slab+0x91/0x300
>>>>     [<ffffffff815de95a>] __slab_alloc+0x2bb/0x482
>>>>     [<ffffffff8105bc1c>] ? copy_process.part.25+0xfc/0x14c0
>>>>     [<ffffffff810a3c78>] ? load_balance+0x218/0x890
>>>>     [<ffffffff8101a679>] ? sched_clock+0x9/0x10
>>>>     [<ffffffff81105ba9>] ? trace_clock_local+0x9/0x10
>>>>     [<ffffffff81193d1c>] kmem_cache_alloc_node+0x8c/0x200
>>>>     [<ffffffff8105bc1c>] copy_process.part.25+0xfc/0x14c0
>>>>     [<ffffffff81114d0d>] ? trace_buffer_unlock_commit+0x4d/0x60
>>>>     [<ffffffff81085a80>] ? kthread_create_on_node+0x140/0x140
>>>>     [<ffffffff8105d0ec>] do_fork+0xbc/0x360
>>>>     [<ffffffff8105d3b6>] kernel_thread+0x26/0x30
>>>>     [<ffffffff81086652>] kthreadd+0x2c2/0x300
>>>>     [<ffffffff81086390>] ? kthread_create_on_cpu+0x60/0x60
>>>>     [<ffffffff815f20ec>] ret_from_fork+0x7c/0xb0
>>>>     [<ffffffff81086390>] ? kthread_create_on_cpu+0x60/0x60
>>>>
>>>> In my investigation, I found the root cause is wq_numa_possible_cpumask.
>>>> All entries of wq_numa_possible_cpumask is allocated by
>>>> alloc_cpumask_var_node(). And these entries are used without initializing.
>>>> So these entries have wrong value.
>>>>
>>>> When hot-adding and onlining CPU, wq_update_unbound_numa() is called.
>>>> wq_update_unbound_numa() calls alloc_unbound_pwq(). And alloc_unbound_pwq()
>>>> calls get_unbound_pool(). In get_unbound_pool(), worker_pool->node is set
>>>> as follow:
>>>>
>>>> #kernel/workqueue.c
>>>> 3592         /* if cpumask is contained inside a NUMA node, we belong to that node */
>>>> 3593         if (wq_numa_enabled) {
>>>> 3594                 for_each_node(node) {
>>>> 3595                         if (cpumask_subset(pool->attrs->cpumask,
>>>> 3596                                            wq_numa_possible_cpumask[node])) {
>>>> 3597                                 pool->node = node;
>>>> 3598                                 break;
>>>> 3599                         }
>>>> 3600                 }
>>>> 3601         }
>>>>
>>>> But wq_numa_possible_cpumask[node] does not have correct cpumask. So, wrong
>>>> node is selected. As a result, kernel panic occurs.
>>>>
>>>> By this patch, all entries of wq_numa_possible_cpumask are allocated by
>>>> zalloc_cpumask_var_node to initialize them. And the panic disappeared.
>
> Hi, Yasuaki
>

> You said the panic disappeared with the old patch, how did it happen
> since the old patch was considered incorrect?
>
> Did the panic happen so rarely that it was mistaken disappeared?
>
> How did you test the new one?

I tested new patch. And I confirmed the panic disappeared.

The patch is one liner.  So after testing correct patch (new one), I wrote
a patch into my tree by hand not use git format-patch/am command. Then I mistook
to create old patch and send it.

So I tested new patch and didn't test old patch.
Sorry for my mistake.

>
> In the point of review, we definitely need to use zalloc_cpumask_var_node()
> instead of alloc_cpumask_var_node() in wq_numa_init().
>
> So for the new patch:
>

> Reviewed-by: Lai Jiangshan <laijs@...fujitsu.com>
Thanks for your review.

Thanks,
Yasuaki Ishimatsu

>
> Thanks,
> Lai
>
>>>>
>>>> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
>>>
>>> Hi, Yasuaki
>>>
>>> All cpumasks in the wq_numa_possible_cpumask array are allocated in
>>> wq_numa_init():
>>>
>>>      for_each_node(node)
>>>          BUG_ON(!alloc_cpumask_var_node(&tbl[node], GFP_KERNEL,
>>>                  node_online(node) ? node : NUMA_NO_NODE));
>>>
>>>      [snip...]
>>>
>>>      wq_numa_possible_cpumask = tbl;
>>>
>>> I didn't find out how does this patch make the all entries of
>>> wq_numa_possible_cpumask zeroed.
>>
>> Sorry. I mistook. I will resend soon.
>>
>> Thanks,
>> Yasuaki Ishimatsu.
>>
>>>
>>> Or I misunderstood.
>>>
>>> Thanks,
>>> Lai
>>>
>>>> ---
>>>>    kernel/workqueue.c | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
>>>> index 6203d29..b393ded 100644
>>>> --- a/kernel/workqueue.c
>>>> +++ b/kernel/workqueue.c
>>>> @@ -3338,7 +3338,7 @@ struct workqueue_attrs *alloc_workqueue_attrs(gfp_t gfp_mask)
>>>>        attrs = kzalloc(sizeof(*attrs), gfp_mask);
>>>>        if (!attrs)
>>>>            goto fail;
>>>> -    if (!alloc_cpumask_var(&attrs->cpumask, gfp_mask))
>>>> +    if (!zalloc_cpumask_var(&attrs->cpumask, gfp_mask))
>>>>            goto fail;
>>>>
>>>>        cpumask_copy(attrs->cpumask, cpu_possible_mask);
>>>>
>>>> .
>>>>
>>>
>>
>>
>> .
>>
>


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