linux-kernel - Re: [PATCH] driver core: ensure a device has valid node id in device

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Date:   Tue, 10 Sep 2019 14:53:39 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Yunsheng Lin <linyunsheng@...wei.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, rafael@...nel.org,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...nel.org, linuxarm@...wei.com
Subject: Re: [PATCH] driver core: ensure a device has valid node id in
 device_add()

On Tue 10-09-19 20:47:40, Yunsheng Lin wrote:
> On 2019/9/10 19:12, Greg KH wrote:
> > On Tue, Sep 10, 2019 at 01:04:51PM +0200, Michal Hocko wrote:
> >> On Tue 10-09-19 18:58:05, Yunsheng Lin wrote:
> >>> On 2019/9/10 17:31, Greg KH wrote:
> >>>> On Tue, Sep 10, 2019 at 02:43:32PM +0800, Yunsheng Lin wrote:
> >>>>> On 2019/9/9 17:53, Greg KH wrote:
> >>>>>> On Mon, Sep 09, 2019 at 02:04:23PM +0800, Yunsheng Lin wrote:
> >>>>>>> Currently a device does not belong to any of the numa nodes
> >>>>>>> (dev->numa_node is NUMA_NO_NODE) when the node id is neither
> >>>>>>> specified by fw nor by virtual device layer and the device has
> >>>>>>> no parent device.
> >>>>>>
> >>>>>> Is this really a problem?
> >>>>>
> >>>>> Not really.
> >>>>> Someone need to guess the node id when it is not specified, right?
> >>>>
> >>>> No, why?  Guessing guarantees you will get it wrong on some systems.
> >>>>
> >>>> Are you seeing real problems because the id is not being set?  What
> >>>> problem is this fixing that you can actually observe?
> >>>
> >>> When passing the return value of dev_to_node() to cpumask_of_node()
> >>> without checking the node id if the node id is not valid, there is
> >>> global-out-of-bounds detected by KASAN as below:
> >>
> >> OK, I seem to remember this being brought up already. And now when I
> >> think about it, we really want to make cpumask_of_node NUMA_NO_NODE
> >> aware. That means using the same trick the allocator does for this
> >> special case.
> > 
> > That seems reasonable to me, and much more "obvious" as to what is going
> > on.
> > 
> 
> Ok, thanks for the suggestion.
> 
> For arm64 and x86, there are two versions of cpumask_of_node().
> 
> when CONFIG_DEBUG_PER_CPU_MAPS is defined, the cpumask_of_node()
>    in arch/x86/mm/numa.c is used, which does partial node id checking:
> 
> const struct cpumask *cpumask_of_node(int node)
> {
>         if (node >= nr_node_ids) {
>                 printk(KERN_WARNING
>                         "cpumask_of_node(%d): node > nr_node_ids(%u)\n",
>                         node, nr_node_ids);
>                 dump_stack();
>                 return cpu_none_mask;
>         }
>         if (node_to_cpumask_map[node] == NULL) {
>                 printk(KERN_WARNING
>                         "cpumask_of_node(%d): no node_to_cpumask_map!\n",
>                         node);
>                 dump_stack();
>                 return cpu_online_mask;
>         }
>         return node_to_cpumask_map[node];
> }
> 
> when CONFIG_DEBUG_PER_CPU_MAPS is undefined, the cpumask_of_node()
>    in arch/x86/include/asm/topology.h is used:
> 
> static inline const struct cpumask *cpumask_of_node(int node)
> {
>         return node_to_cpumask_map[node];
> }

I would simply go with. There shouldn't be any need for heavy weight
checks that CONFIG_DEBUG_PER_CPU_MAPS has.

static inline const struct cpumask *cpumask_of_node(int node)
{
	/* A nice comment goes here */
	if (node == NUMA_NO_NODE)
		return node_to_cpumask_map[numa_mem_id()];
        return node_to_cpumask_map[node];
}
-- 
Michal Hocko
SUSE Labs