On 06/04/2020 12:00 PM, Peter Zijlstra wrote:
On Thu, Jun 04, 2020 at 12:17:23PM +0100, Will Deacon wrote:
Hi, [+Peter]
On Thu, Jun 04, 2020 at 10:48:03AM +0000, Christophe Leroy wrote:
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:
At first glance, this looks like a real bug in the 16k page code -- you're
loading the pte non-atomically on the fast GUP path and so you're prone to
tearing, which probably isn't what you want. For a short-term hack, I'd
suggest having CONFIG_HAVE_FAST_GUP depend on !CONFIG_PPC_16K_PAGES, but if
you want to support this them you'll need to rework your pte_t so that it
can be loaded atomically.
Looking at commit 55c8fc3f49302, they're all the exact same value, so
what they could do is grow another special gup_get_pte() variant that
just loads the first value.
Also, per that very same commit, there's a distinct lack of WRITE_ONCE()
in the pte_update() / __set_pte_at() paths for much of Power.
Thanks for the idea.
Now I get the same issue at
CC mm/mincore.o
In file included from ./include/asm-generic/bug.h:5:0,
from ./arch/powerpc/include/asm/bug.h:109,
from ./include/linux/bug.h:5,
from ./include/linux/mmdebug.h:5,
from ./include/linux/mm.h:9,
from ./include/linux/pagemap.h:8,
from mm/mincore.c:11:
In function 'huge_ptep_get',
inlined from 'mincore_hugetlb' at mm/mincore.c:35:20:
./include/linux/compiler.h:392:38: error: call to
'__compiletime_assert_218' 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); \
^
./include/asm-generic/hugetlb.h:125:9: note: in expansion of macro
'READ_ONCE'
return READ_ONCE(*ptep);
^
make[2]: *** [mm/mincore.o] Error 1
I guess for this one I have to implement platform specific huge_ptep_get()
Christophe
