On Fri, 2 Jan 2015 11:31:36 +0100
Heiko Carstens <heiko.carstens@xxxxxxxxxx> wrote:
> On Wed, Dec 31, 2014 at 12:56:59AM -0500, Mike Frysinger wrote:
> > i've configured my kernel to have:
> > CONFIG_KVM=y
> > CONFIG_NR_CPUS=2
> > CONFIG_SPLIT_PTLOCK_CPUS=4
> >
> > and that makes the build very unhappy:
> > CC arch/s390/mm/pgtable.o
> > arch/s390/mm/pgtable.c: In function ‘__gmap_segment_gaddr’:
> > arch/s390/mm/pgtable.c:327:2: error: implicit declaration of function
> > ‘pmd_to_page’ [-Werror=implicit-function-declaration]
> > page = pmd_to_page((pmd_t *) entry);
> > ^
> >
> > this is because include/linux/mm_types.h has:
> > #define USE_SPLIT_PMD_PTLOCKS (USE_SPLIT_PTE_PTLOCKS && \
> > IS_ENABLED(CONFIG_ARCH_ENABLE_SPLIT_PMD_PTLOCK))
> >
> > and include/linux/mm.h has:
> > #if USE_SPLIT_PMD_PTLOCKS
> > static struct page *pmd_to_page(pmd_t *pmd)
> > ...
> >
> > i did set NR_CPUS down on purpose (this system only has two cpus), but
> > apparently tweaking SPLIT_PTLOCK_CPUS isn't an option :). in mm/Kconfig:
> > config SPLIT_PTLOCK_CPUS
> > int
> > default "4"
> > -mike
>
> Thanks for reporting. The patch below should fix it (adding Martin to To:)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index f80d0194c9bc..4ee25aea7861 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1555,14 +1555,14 @@ static inline void pgtable_page_dtor(struct page *page)
> ((unlikely(pmd_none(*(pmd))) && __pte_alloc_kernel(pmd, address))? \
> NULL: pte_offset_kernel(pmd, address))
>
> -#if USE_SPLIT_PMD_PTLOCKS
> -
> -static struct page *pmd_to_page(pmd_t *pmd)
> +static inline struct page *pmd_to_page(pmd_t *pmd)
> {
> unsigned long mask = ~(PTRS_PER_PMD * sizeof(pmd_t) - 1);
> return virt_to_page((void *)((unsigned long) pmd & mask));
> }
>
> +#if USE_SPLIT_PMD_PTLOCKS
> +
> static inline spinlock_t *pmd_lockptr(struct mm_struct *mm, pmd_t *pmd)
> {
> return ptlock_ptr(pmd_to_page(pmd));
That looks good, there is no reason why the pmd_to_page helper should be
conditional on the USE_SPLIT_PMD_PTLOCKS define.
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.
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