On Fri, Aug 9, 2019 at 8:36 PM Michael Ellerman <m...@ellerman.id.au> wrote: > > Chuhong Yuan <hsleste...@gmail.com> writes: > > Reference counters are preferred to use refcount_t instead of > > atomic_t. > > This is because the implementation of refcount_t can prevent > > overflows and detect possible use-after-free. > > So convert atomic_t ref counters to refcount_t. > > > > Signed-off-by: Chuhong Yuan <hsleste...@gmail.com> > > Thanks. > > We don't have a fast implementation of refcount_t, so I'm worried this > could cause a measurable performance regression. > > Did you benchmark it at all? >
I did not benchmark it and I don't have the testing environment... > cheers > > > diff --git a/arch/powerpc/mm/book3s64/mmu_context.c > > b/arch/powerpc/mm/book3s64/mmu_context.c > > index 2d0cb5ba9a47..f836fd5a6abc 100644 > > --- a/arch/powerpc/mm/book3s64/mmu_context.c > > +++ b/arch/powerpc/mm/book3s64/mmu_context.c > > @@ -231,7 +231,7 @@ static void pmd_frag_destroy(void *pmd_frag) > > /* drop all the pending references */ > > count = ((unsigned long)pmd_frag & ~PAGE_MASK) >> PMD_FRAG_SIZE_SHIFT; > > /* We allow PTE_FRAG_NR fragments from a PTE page */ > > - if (atomic_sub_and_test(PMD_FRAG_NR - count, > > &page->pt_frag_refcount)) { > > + if (refcount_sub_and_test(PMD_FRAG_NR - count, > > &page->pt_frag_refcount)) { > > pgtable_pmd_page_dtor(page); > > __free_page(page); > > } > > diff --git a/arch/powerpc/mm/book3s64/pgtable.c > > b/arch/powerpc/mm/book3s64/pgtable.c > > index 7d0e0d0d22c4..40056896ce4e 100644 > > --- a/arch/powerpc/mm/book3s64/pgtable.c > > +++ b/arch/powerpc/mm/book3s64/pgtable.c > > @@ -277,7 +277,7 @@ static pmd_t *__alloc_for_pmdcache(struct mm_struct *mm) > > return NULL; > > } > > > > - atomic_set(&page->pt_frag_refcount, 1); > > + refcount_set(&page->pt_frag_refcount, 1); > > > > ret = page_address(page); > > /* > > @@ -294,7 +294,7 @@ static pmd_t *__alloc_for_pmdcache(struct mm_struct *mm) > > * count. > > */ > > if (likely(!mm->context.pmd_frag)) { > > - atomic_set(&page->pt_frag_refcount, PMD_FRAG_NR); > > + refcount_set(&page->pt_frag_refcount, PMD_FRAG_NR); > > mm->context.pmd_frag = ret + PMD_FRAG_SIZE; > > } > > spin_unlock(&mm->page_table_lock); > > @@ -317,8 +317,7 @@ void pmd_fragment_free(unsigned long *pmd) > > { > > struct page *page = virt_to_page(pmd); > > > > - BUG_ON(atomic_read(&page->pt_frag_refcount) <= 0); > > - if (atomic_dec_and_test(&page->pt_frag_refcount)) { > > + if (refcount_dec_and_test(&page->pt_frag_refcount)) { > > pgtable_pmd_page_dtor(page); > > __free_page(page); > > } > > diff --git a/arch/powerpc/mm/pgtable-frag.c b/arch/powerpc/mm/pgtable-frag.c > > index a7b05214760c..4ef8231b677f 100644 > > --- a/arch/powerpc/mm/pgtable-frag.c > > +++ b/arch/powerpc/mm/pgtable-frag.c > > @@ -24,7 +24,7 @@ void pte_frag_destroy(void *pte_frag) > > /* drop all the pending references */ > > count = ((unsigned long)pte_frag & ~PAGE_MASK) >> PTE_FRAG_SIZE_SHIFT; > > /* We allow PTE_FRAG_NR fragments from a PTE page */ > > - if (atomic_sub_and_test(PTE_FRAG_NR - count, > > &page->pt_frag_refcount)) { > > + if (refcount_sub_and_test(PTE_FRAG_NR - count, > > &page->pt_frag_refcount)) { > > pgtable_page_dtor(page); > > __free_page(page); > > } > > @@ -71,7 +71,7 @@ static pte_t *__alloc_for_ptecache(struct mm_struct *mm, > > int kernel) > > return NULL; > > } > > > > - atomic_set(&page->pt_frag_refcount, 1); > > + refcount_set(&page->pt_frag_refcount, 1); > > > > ret = page_address(page); > > /* > > @@ -87,7 +87,7 @@ static pte_t *__alloc_for_ptecache(struct mm_struct *mm, > > int kernel) > > * count. > > */ > > if (likely(!pte_frag_get(&mm->context))) { > > - atomic_set(&page->pt_frag_refcount, PTE_FRAG_NR); > > + refcount_set(&page->pt_frag_refcount, PTE_FRAG_NR); > > pte_frag_set(&mm->context, ret + PTE_FRAG_SIZE); > > } > > spin_unlock(&mm->page_table_lock); > > @@ -110,8 +110,7 @@ void pte_fragment_free(unsigned long *table, int kernel) > > { > > struct page *page = virt_to_page(table); > > > > - BUG_ON(atomic_read(&page->pt_frag_refcount) <= 0); > > - if (atomic_dec_and_test(&page->pt_frag_refcount)) { > > + if (refcount_dec_and_test(&page->pt_frag_refcount)) { > > if (!kernel) > > pgtable_page_dtor(page); > > __free_page(page); > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > > index 3a37a89eb7a7..7fe23a3faf95 100644 > > --- a/include/linux/mm_types.h > > +++ b/include/linux/mm_types.h > > @@ -14,6 +14,7 @@ > > #include <linux/uprobes.h> > > #include <linux/page-flags-layout.h> > > #include <linux/workqueue.h> > > +#include <linux/refcount.h> > > > > #include <asm/mmu.h> > > > > @@ -147,7 +148,7 @@ struct page { > > unsigned long _pt_pad_2; /* mapping */ > > union { > > struct mm_struct *pt_mm; /* x86 pgds only */ > > - atomic_t pt_frag_refcount; /* powerpc */ > > + refcount_t pt_frag_refcount; /* powerpc */ > > }; > > #if ALLOC_SPLIT_PTLOCKS > > spinlock_t *ptl; > > -- > > 2.20.1