Re: [perf/x86] 75925e1ad7: BUG: unable to handle kernel paging request at 000045b8

[Peter Zijlstra]

On Fri, Jan 22, 2016 at 12:33:24PM +0800, kernel test robot wrote:
> Greetings,
> 
> 0day kernel testing robot got the below dmesg and the first bad commit is
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> 
> commit 75925e1ad7f5a4e867bd14ff8e7f114ea1596434
> Author:     Andi Kleen <ak@xxxxxxxxxxxxxxx>
> AuthorDate: Thu Oct 22 15:07:21 2015 -0700
> Commit:     Ingo Molnar <mingo@xxxxxxxxxx>
> CommitDate: Mon Nov 23 09:58:25 2015 +0100
> 
>     perf/x86: Optimize stack walk user accesses
>     
>     Change the perf user stack walking to use the new
>     __copy_from_user_nmi(), and split each access into word sized transfer
>     sizes. This allows to inline the complete access and optimize it all
>     into a single load.

Andi, please have a look at this. Also note that x86_64
__copy_from_user_nocheck() actually supports .size=16.