2019-08-08 07:19:20

by Chuhong Yuan

Subject: [PATCH 1/2] s390/extmem: 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/mm/extmem.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/s390/mm/extmem.c b/arch/s390/mm/extmem.c
index 0b5622714c12..78e801287c72 100644
--- a/arch/s390/mm/extmem.c
+++ b/arch/s390/mm/extmem.c
@@ -19,6 +19,7 @@
#include <linux/memblock.h>
#include <linux/ctype.h>
#include <linux/ioport.h>
+#include <linux/refcount.h>
#include <asm/diag.h>
#include <asm/page.h>
#include <asm/pgtable.h>
@@ -64,7 +65,7 @@ struct dcss_segment {
char res_name[16];
unsigned long start_addr;
unsigned long end;
- atomic_t ref_count;
+ refcount_t ref_count;
int do_nonshared;
unsigned int vm_segtype;
struct qrange range[6];
@@ -362,7 +363,7 @@ __segment_load (char *name, int do_nonshared, unsigned long *addr, unsigned long
seg->start_addr = start_addr;
seg->end = end_addr;
seg->do_nonshared = do_nonshared;
- atomic_set(&seg->ref_count, 1);
+ refcount_set(&seg->ref_count, 1);
list_add(&seg->list, &dcss_list);
*addr = seg->start_addr;
*end = seg->end;
@@ -422,7 +423,7 @@ segment_load (char *name, int do_nonshared, unsigned long *addr,
rc = __segment_load (name, do_nonshared, addr, end);
else {
if (do_nonshared == seg->do_nonshared) {
- atomic_inc(&seg->ref_count);
+ refcount_inc(&seg->ref_count);
*addr = seg->start_addr;
*end = seg->end;
rc = seg->vm_segtype;
@@ -468,7 +469,7 @@ segment_modify_shared (char *name, int do_nonshared)
rc = 0;
goto out_unlock;
}
- if (atomic_read (&seg->ref_count) != 1) {
+ if (refcount_read(&seg->ref_count) != 1) {
pr_warn("DCSS %s is in use and cannot be reloaded\n", name);
rc = -EAGAIN;
goto out_unlock;
@@ -544,7 +545,7 @@ segment_unload(char *name)
pr_err("Unloading unknown DCSS %s failed\n", name);
goto out_unlock;
}
- if (atomic_dec_return(&seg->ref_count) != 0)
+ if (!refcount_dec_and_test(&seg->ref_count))
goto out_unlock;
release_resource(seg->res);
kfree(seg->res);
--
2.20.1

2019-08-08 11:37:04

by Heiko Carstens

Subject: Re: [PATCH 1/2] s390/extmem: Use refcount_t for refcount

On Thu, Aug 08, 2019 at 03:18:17PM +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/mm/extmem.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)

Applied, thanks.