2019-08-08 07:40:07

by Chuhong Yuan

Subject: [PATCH 2/2] s390/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 <[email protected]>
---
arch/s390/include/asm/gmap.h | 4 +++-
arch/s390/mm/gmap.c | 10 +++++-----
2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/s390/include/asm/gmap.h b/arch/s390/include/asm/gmap.h
index fcbd638fb9f4..37f96b6f0e61 100644
--- a/arch/s390/include/asm/gmap.h
+++ b/arch/s390/include/asm/gmap.h
@@ -9,6 +9,8 @@
#ifndef _ASM_S390_GMAP_H
#define _ASM_S390_GMAP_H

+#include <linux/refcount.h>
+
/* Generic bits for GMAP notification on DAT table entry changes. */
#define GMAP_NOTIFY_SHADOW 0x2
#define GMAP_NOTIFY_MPROT 0x1
@@ -46,7 +48,7 @@ struct gmap {
struct radix_tree_root guest_to_host;
struct radix_tree_root host_to_guest;
spinlock_t guest_table_lock;
- atomic_t ref_count;
+ refcount_t ref_count;
unsigned long *table;
unsigned long asce;
unsigned long asce_end;
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 39c3a6e3d262..cd8e03f04d6d 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -67,7 +67,7 @@ static struct gmap *gmap_alloc(unsigned long limit)
INIT_RADIX_TREE(&gmap->host_to_rmap, GFP_ATOMIC);
spin_lock_init(&gmap->guest_table_lock);
spin_lock_init(&gmap->shadow_lock);
- atomic_set(&gmap->ref_count, 1);
+ refcount_set(&gmap->ref_count, 1);
page = alloc_pages(GFP_KERNEL, CRST_ALLOC_ORDER);
if (!page)
goto out_free;
@@ -214,7 +214,7 @@ static void gmap_free(struct gmap *gmap)
*/
struct gmap *gmap_get(struct gmap *gmap)
{
- atomic_inc(&gmap->ref_count);
+ refcount_inc(&gmap->ref_count);
return gmap;
}
EXPORT_SYMBOL_GPL(gmap_get);
@@ -227,7 +227,7 @@ EXPORT_SYMBOL_GPL(gmap_get);
*/
void gmap_put(struct gmap *gmap)
{
- if (atomic_dec_return(&gmap->ref_count) == 0)
+ if (refcount_dec_and_test(&gmap->ref_count))
gmap_free(gmap);
}
EXPORT_SYMBOL_GPL(gmap_put);
@@ -1594,7 +1594,7 @@ static struct gmap *gmap_find_shadow(struct gmap *parent, unsigned long asce,
continue;
if (!sg->initialized)
return ERR_PTR(-EAGAIN);
- atomic_inc(&sg->ref_count);
+ refcount_inc(&sg->ref_count);
return sg;
}
return NULL;
@@ -1682,7 +1682,7 @@ struct gmap *gmap_shadow(struct gmap *parent, unsigned long asce,
}
}
}
- atomic_set(&new->ref_count, 2);
+ refcount_set(&new->ref_count, 2);
list_add(&new->list, &parent->children);
if (asce & _ASCE_REAL_SPACE) {
/* nothing to protect, return right away */
--
2.20.1

2019-08-08 07:54:26

by Cornelia Huck

Subject: Re: [PATCH 2/2] s390/mm: Use refcount_t for refcount

On Thu, 8 Aug 2019 15:18:26 +0800
Chuhong Yuan <[email protected]> wrote:

> 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 <[email protected]>
> ---
> arch/s390/include/asm/gmap.h | 4 +++-
> arch/s390/mm/gmap.c | 10 +++++-----
> 2 files changed, 8 insertions(+), 6 deletions(-)

Reviewed-by: Cornelia Huck <[email protected]>

2019-08-08 11:38:41

by Heiko Carstens

Subject: Re: [PATCH 2/2] s390/mm: Use refcount_t for refcount

On Thu, Aug 08, 2019 at 03:18:26PM +0800, Chuhong Yuan wrote:
> 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 <[email protected]>
> ---
> arch/s390/include/asm/gmap.h | 4 +++-
> arch/s390/mm/gmap.c | 10 +++++-----
> 2 files changed, 8 insertions(+), 6 deletions(-)

Applied, thanks.