Benjamin Herrenschmidt wrote:
>> --- Exception: 301 at .memset+0x60/0xfc
>>     LR = .pcpu_alloc+0x718/0x8fc
> 
> So it's memsetting something that causes it to hash_page(), ie, faulting
> in pages (vmalloc space ?) so far nothing obviously wrong....

It's probably memset() call near the end of pcpu_populate_chunk()
where percpu allocator clears the allocated areas before returning to
user.  I don't think the first chunk is causing the problem as they're
all in the linear mapped area.  From the second chunk on, they're on
vmalloc area and very near to the top of it, so that might be exposing
a hidden problem in paging code?  BTW, for some reason, the problem is
not reproducible on my powerstation.

Sachin, can you please apply the attached patch on top of the current
linus tree, reproduce the hang and report full kernel log?  Let's see
which address is causing the problem.

Thanks.

-- 
tejun