Messages in this thread | | | Date | Fri, 26 Nov 2021 18:55:40 +0100 | Subject | Re: [PATCH] powerpc/mm: Use refcount_t for refcount | From | Christophe Leroy <> |
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Le 09/08/2019 à 14:36, Michael Ellerman a écrit : > Chuhong Yuan <hslester96@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 <hslester96@gmail.com> > > Thanks. > > We don't have a fast implementation of refcount_t, so I'm worried this > could cause a measurable performance regression.
Fast implementations have been removed by commit https://github.com/linuxppc/linux/commit/fb041bb7c0a918b95c6889fc965cdc4a75b4c0ca
It's now considered that the generic implementation is good enough for everybody.
However, this series doesn't apply anymore and needs rebase:
Applying: powerpc/mm: Use refcount_t for refcount Using index info to reconstruct a base tree... M arch/powerpc/mm/book3s64/mmu_context.c M arch/powerpc/mm/book3s64/pgtable.c M arch/powerpc/mm/pgtable-frag.c M include/linux/mm_types.h Falling back to patching base and 3-way merge... Auto-merging include/linux/mm_types.h CONFLICT (content): Merge conflict in include/linux/mm_types.h Auto-merging arch/powerpc/mm/pgtable-frag.c CONFLICT (content): Merge conflict in arch/powerpc/mm/pgtable-frag.c Auto-merging arch/powerpc/mm/book3s64/pgtable.c CONFLICT (content): Merge conflict in arch/powerpc/mm/book3s64/pgtable.c Auto-merging arch/powerpc/mm/book3s64/mmu_context.c Patch failed at 0001 powerpc/mm: Use refcount_t for refcount When you have resolved this problem, run "git am --continue". If you prefer to skip this patch, run "git am --skip" instead. To restore the original branch and stop patching, run "git am --abort".
Thanks Christophe
> > Did you benchmark it at all? > > 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
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