linux-next: build failure on powerpc 8xx with 16k pages

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Hi all,

Using mpc885_ads_defconfig with CONFIG_PPC_16K_PAGES instead of 
CONFIG_PPC_4K_PAGES, getting the following build failure:

   CC      mm/gup.o
In file included from ./include/linux/kernel.h:11:0,
                  from mm/gup.c:2:
In function 'gup_hugepte.constprop',
     inlined from 'gup_huge_pd.isra.78' at mm/gup.c:2465:8:
./include/linux/compiler.h:392:38: error: call to 
'__compiletime_assert_257' declared with attribute error: Unsupported 
access size for {READ,WRITE}_ONCE().
   _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
                                       ^
./include/linux/compiler.h:373:4: note: in definition of macro 
'__compiletime_assert'
     prefix ## suffix();    \
     ^
./include/linux/compiler.h:392:2: note: in expansion of macro 
'_compiletime_assert'
   _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
   ^
./include/linux/compiler.h:405:2: note: in expansion of macro 
'compiletime_assert'
   compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long), \
   ^
./include/linux/compiler.h:291:2: note: in expansion of macro 
'compiletime_assert_rwonce_type'
   compiletime_assert_rwonce_type(x);    \
   ^
mm/gup.c:2428:8: note: in expansion of macro 'READ_ONCE'
   pte = READ_ONCE(*ptep);
         ^
In function 'gup_get_pte',
     inlined from 'gup_pte_range' at mm/gup.c:2228:9,
     inlined from 'gup_pmd_range' at mm/gup.c:2613:15,
     inlined from 'gup_pud_range' at mm/gup.c:2641:15,
     inlined from 'gup_p4d_range' at mm/gup.c:2666:15,
     inlined from 'gup_pgd_range' at mm/gup.c:2694:15,
     inlined from 'internal_get_user_pages_fast' at mm/gup.c:2785:3:
./include/linux/compiler.h:392:38: error: call to 
'__compiletime_assert_254' declared with attribute error: Unsupported 
access size for {READ,WRITE}_ONCE().
   _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
                                       ^
./include/linux/compiler.h:373:4: note: in definition of macro 
'__compiletime_assert'
     prefix ## suffix();    \
     ^
./include/linux/compiler.h:392:2: note: in expansion of macro 
'_compiletime_assert'
   _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
   ^
./include/linux/compiler.h:405:2: note: in expansion of macro 
'compiletime_assert'
   compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long), \
   ^
./include/linux/compiler.h:291:2: note: in expansion of macro 
'compiletime_assert_rwonce_type'
   compiletime_assert_rwonce_type(x);    \
   ^
mm/gup.c:2199:9: note: in expansion of macro 'READ_ONCE'
   return READ_ONCE(*ptep);
          ^
make[2]: *** [mm/gup.o] Error 1


Bisected to:

2ab3a0a02905 (HEAD, refs/bisect/bad) READ_ONCE: Enforce atomicity for 
{READ,WRITE}_ONCE() memory accesses

Christophe