Re: [PATCH] workqueue: initialize cpumask of wq_numa_possible_cpumask

[Yasuaki Ishimatsu]

(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.
> >
> > Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
>
> 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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