Kernel 4.15 lost set_robust_list support on POWER 9

[Mauricio Faria de Oliveira]

Nick, Michael,

On 02/05/2018 10:48 AM, Florian Weimer wrote:
> 7041  set_robust_list(0x7fff93dc3980, 24) = -1 ENOSYS (Function not 
> implemented)

The regression was introduced by commit 371b8044 ("powerpc/64s: 
Initialize ISAv3 MMU registers before setting partition table").

The problem is Radix MMU specific (does not occur with 'disable_radix'),
and does not occur with that code reverted (ie do not set PIDR to zero).

Do you see any reasons why?
(wondering if at all related to access_ok() in include/asm/uaccess.h)

with:

     # strace -e set_robust_list -f ./test
     set_robust_list(0x7fffa4b03910, 24)     = -1 ENOSYS (Function not 
implemented)
     +++ exited with 1 +++

     # uname -r
     4.15.0

without:

     # strace -e set_robust_list -f ./test
     set_robust_list(0x7fff889c3910, 24)     = 0
     +++ exited with 0 +++

     # uname -r
     4.15.0.nopidr