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Date:	Mon, 7 Jul 2014 08:19:04 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
CC:	<tj@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] workqueue: initialize cpumask of wq_numa_possible_cpumask

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.
> 
> 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.

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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