Re: [PATCH] powerpc/mm: Use refcount_t for refcount
Le 09/08/2019 à 14:36, Michael Ellerman a écrit :
Chuhong Yuan 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
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, >pt_frag_refcount)) {
+ if (refcount_sub_and_test(PMD_FRAG_NR - count,
>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(>pt_frag_refcount, 1);
+ refcount_set(>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(>pt_frag_refcount, PMD_FRAG_NR);
+ refcount_set(>pt_frag_refcount, PMD_FRAG_NR);
mm->context.pmd_frag = ret + PMD_FRAG_SIZE;
}
spin_unlock(>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(>pt_frag_refcount) <= 0);
- if (atomic_dec_and_test(>pt_frag_refcount)) {
+ if (refcount_dec_and_test(>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, >pt_frag_refcount)) {
+ if (refcount_sub_and_test(PTE_FRAG_NR - count,
>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(>pt_frag_refcount, 1);
+ refcount_set(>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(>context))) {
- atomic_set(>pt_frag_refcount, PTE_FRAG_NR);
+ refcount_set(>pt_frag_refcount, PTE_FRAG_NR);
pte_frag_set(>context, ret + PTE_FRAG_SIZE);
}
Re: [PATCH] powerpc/mm: Use refcount_t for refcount
On Fri, Aug 9, 2019 at 8:36 PM Michael Ellerman wrote:
>
> Chuhong Yuan 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
>
> 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,
> > >pt_frag_refcount)) {
> > + if (refcount_sub_and_test(PMD_FRAG_NR - count,
> > >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(>pt_frag_refcount, 1);
> > + refcount_set(>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(>pt_frag_refcount, PMD_FRAG_NR);
> > + refcount_set(>pt_frag_refcount, PMD_FRAG_NR);
> > mm->context.pmd_frag = ret + PMD_FRAG_SIZE;
> > }
> > spin_unlock(>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(>pt_frag_refcount) <= 0);
> > - if (atomic_dec_and_test(>pt_frag_refcount)) {
> > + if (refcount_dec_and_test(>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,
> > >pt_frag_refcount)) {
> > + if (refcount_sub_and_test(PTE_FRAG_NR - count,
> > >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(>pt_frag_refcount, 1);
> > + refcount_set(>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(>context))) {
> > - atomic_set(>pt_frag_refcount, PTE_FRAG_NR);
> > + refcount_set(>pt_frag_refcount, PTE_FRAG_NR);
> > pte_frag_set(>context, ret + PTE_FRAG_SIZE);
> > }
> > spin_unlock(>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(>pt_frag_refcount) <= 0);
> > - if (atomic_dec_and_test(>pt_frag_refcount)) {
> > + if (refcount_dec_and_test(>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
> > #include
> > #include
> > +#include
> >
> > #include
> >
> > @@ -147,7 +148,7 @@ struct page {
> > unsigned long _pt_pad_2;/* mapping */
> > union {
> >
Re: [PATCH] powerpc/mm: Use refcount_t for refcount
Chuhong Yuan 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
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?
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, >pt_frag_refcount)) {
> + if (refcount_sub_and_test(PMD_FRAG_NR - count,
> >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(>pt_frag_refcount, 1);
> + refcount_set(>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(>pt_frag_refcount, PMD_FRAG_NR);
> + refcount_set(>pt_frag_refcount, PMD_FRAG_NR);
> mm->context.pmd_frag = ret + PMD_FRAG_SIZE;
> }
> spin_unlock(>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(>pt_frag_refcount) <= 0);
> - if (atomic_dec_and_test(>pt_frag_refcount)) {
> + if (refcount_dec_and_test(>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, >pt_frag_refcount)) {
> + if (refcount_sub_and_test(PTE_FRAG_NR - count,
> >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(>pt_frag_refcount, 1);
> + refcount_set(>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(>context))) {
> - atomic_set(>pt_frag_refcount, PTE_FRAG_NR);
> + refcount_set(>pt_frag_refcount, PTE_FRAG_NR);
> pte_frag_set(>context, ret + PTE_FRAG_SIZE);
> }
> spin_unlock(>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(>pt_frag_refcount) <= 0);
> - if (atomic_dec_and_test(>pt_frag_refcount)) {
> + if (refcount_dec_and_test(>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
> #include
> #include
> +#include
>
> #include
>
> @@ -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
[PATCH] powerpc/mm: Use refcount_t for refcount
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
---
arch/powerpc/mm/book3s64/mmu_context.c | 2 +-
arch/powerpc/mm/book3s64/pgtable.c | 7 +++
arch/powerpc/mm/pgtable-frag.c | 9 -
include/linux/mm_types.h | 3 ++-
4 files changed, 10 insertions(+), 11 deletions(-)
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, >pt_frag_refcount)) {
+ if (refcount_sub_and_test(PMD_FRAG_NR - count,
>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(>pt_frag_refcount, 1);
+ refcount_set(>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(>pt_frag_refcount, PMD_FRAG_NR);
+ refcount_set(>pt_frag_refcount, PMD_FRAG_NR);
mm->context.pmd_frag = ret + PMD_FRAG_SIZE;
}
spin_unlock(>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(>pt_frag_refcount) <= 0);
- if (atomic_dec_and_test(>pt_frag_refcount)) {
+ if (refcount_dec_and_test(>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, >pt_frag_refcount)) {
+ if (refcount_sub_and_test(PTE_FRAG_NR - count,
>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(>pt_frag_refcount, 1);
+ refcount_set(>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(>context))) {
- atomic_set(>pt_frag_refcount, PTE_FRAG_NR);
+ refcount_set(>pt_frag_refcount, PTE_FRAG_NR);
pte_frag_set(>context, ret + PTE_FRAG_SIZE);
}
spin_unlock(>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(>pt_frag_refcount) <= 0);
- if (atomic_dec_and_test(>pt_frag_refcount)) {
+ if (refcount_dec_and_test(>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
#include
#include
+#include
#include
@@ -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
