On 09/13/2019 12:41 PM, Christophe Leroy wrote: > > > Le 13/09/2019 à 09:03, Christophe Leroy a écrit : >> >> >> Le 13/09/2019 à 08:58, Anshuman Khandual a écrit : >>> On 09/13/2019 11:53 AM, Christophe Leroy wrote: >>>> Fix build failure on powerpc. >>>> >>>> Fix preemption imbalance. >>>> >>>> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx> >>>> --- >>>> mm/arch_pgtable_test.c | 3 +++ >>>> 1 file changed, 3 insertions(+) >>>> >>>> diff --git a/mm/arch_pgtable_test.c b/mm/arch_pgtable_test.c >>>> index 8b4a92756ad8..f2b3c9ec35fa 100644 >>>> --- a/mm/arch_pgtable_test.c >>>> +++ b/mm/arch_pgtable_test.c >>>> @@ -24,6 +24,7 @@ >>>> #include <linux/swap.h> >>>> #include <linux/swapops.h> >>>> #include <linux/sched/mm.h> >>>> +#include <linux/highmem.h> >>> >>> This is okay. >>> >>>> #include <asm/pgalloc.h> >>>> #include <asm/pgtable.h> >>>> @@ -400,6 +401,8 @@ static int __init arch_pgtable_tests_init(void) >>>> p4d_clear_tests(p4dp); >>>> pgd_clear_tests(mm, pgdp); >>>> + pte_unmap(ptep); >>>> + >>> >>> Now the preemption imbalance via pte_alloc_map() path i.e >>> >>> pte_alloc_map() -> pte_offset_map() -> kmap_atomic() >>> >>> Is not this very much powerpc 32 specific or this will be applicable >>> for all platform which uses kmap_XXX() to map high memory ? >>> >> >> See https://elixir.bootlin.com/linux/v5.3-rc8/source/include/linux/highmem.h#L91 >> >> I think it applies at least to all arches using the generic implementation. >> >> Applies also to arm: >> https://elixir.bootlin.com/linux/v5.3-rc8/source/arch/arm/mm/highmem.c#L52 >> >> Applies also to mips: >> https://elixir.bootlin.com/linux/v5.3-rc8/source/arch/mips/mm/highmem.c#L47 >> >> Same on sparc: >> https://elixir.bootlin.com/linux/v5.3-rc8/source/arch/sparc/mm/highmem.c#L52 >> >> Same on x86: >> https://elixir.bootlin.com/linux/v5.3-rc8/source/arch/x86/mm/highmem_32.c#L34 >> >> I have not checked others, but I guess it is like that for all. >> > > > Seems like I answered too quickly. All kmap_atomic() do preempt_disable(), but not all pte_alloc_map() call kmap_atomic(). > > However, for instance ARM does: > > https://elixir.bootlin.com/linux/v5.3-rc8/source/arch/arm/include/asm/pgtable.h#L200 > > And X86 as well: > > https://elixir.bootlin.com/linux/v5.3-rc8/source/arch/x86/include/asm/pgtable_32.h#L51 > > Microblaze also: > > https://elixir.bootlin.com/linux/v5.3-rc8/source/arch/microblaze/include/asm/pgtable.h#L495 All the above platforms checks out to be using k[un]map_atomic(). I am wondering whether any of the intermediate levels will have similar problems on any these 32 bit platforms or any other platforms which might be using generic k[un]map_atomic(). There can be many permutations here. p4dp = p4d_alloc(mm, pgdp, vaddr); pudp = pud_alloc(mm, p4dp, vaddr); pmdp = pmd_alloc(mm, pudp, vaddr); Otherwise pte_alloc_map()/pte_unmap() looks good enough which will atleast take care of a known failure.
