Messages in this thread | | | Subject | Re: linux-next: build failure on powerpc 8xx with 16k pages | From | Christophe Leroy <> | Date | Thu, 4 Jun 2020 14:35:14 +0000 |
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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
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