Re: [Bugfix] sched: fix possible invalid memory access caused by CPU hot-addition

[Jiang Liu <jiang.liu@linux.intel.com>]

On 2014/4/23 9:59, David Rientjes wrote:
> On Tue, 22 Apr 2014, Peter Zijlstra wrote:
> 
>> On Tue, Apr 22, 2014 at 01:01:51PM -0700, Andrew Morton wrote:
>>> On Tue, 22 Apr 2014 10:15:15 +0200 Peter Zijlstra <peterz@infradead.org> wrote:
>>>
>>>> On Tue, Apr 22, 2014 at 01:27:15PM +0800, Jiang Liu wrote:
>>>>> When calling kzalloc_node(size, flags, node), we should first check
>>>>> whether node is onlined, otherwise it may cause invalid memory access
>>>>> as below.
>>>>
>>>> But this is only for memory less node crap, right? 
>>>
>>> um, why are memoryless nodes crap?
>>
>> Why wouldn't they be? Having CPUs with no local memory seems decidedly
>> suboptimal.
> 
> The quick fix for memoryless node issues is usually just do cpu_to_mem() 
> rather than cpu_to_node() in the caller.  This assumes that the arch is 
> setup correctly to handle memoryless nodes with 
> CONFIG_HAVE_MEMORYLESS_NODES (and we've had problems recently with 
> memoryless nodes not being configured correctly on powerpc).
> 
> That type of a fix would probably be better handled in the slab allocator, 
> though, since kmalloc_node(nid) shouldn't crash just because nid is 
> memoryless, we should be doing local_memory_node(node) when allocating the 
> slab pages.
> 
> However, I don't think memoryless nodes are the problem here since Jiang 
> is testing for !node_online(nid) in his patch, so it's a problem with 
> cpu_to_node() pointing to an offline node.  It makes sense for the page 
> allocator to crash in such a case, the node id is erroneous.
> 
> So either the cpu-to-node mapping is invalid or alloc_fair_sched_group() 
> is allocating memory for a cpu on an offline node.  The 
> for_each_possible_cpu() looks suspicious.  There's no guarantee that 
> local_memory_node(node) for an offline node will return anything with 
> affinity, so falling back to NUMA_NO_NODE looks appropriate in Jiang's 
> patch.
Hi David,
	That's the case, alloc_fair_sched_group() is trying to allocate
memory for CPU in offline node, which then access non-exist NODE_DATA.
Thanks!
Gerry

>