[Xen-devel] [PATCH 3/3] xen/blkback: Use refcount_t for refcount

[Chuhong Yuan <hslester96@xxxxxxxxx>]

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@xxxxxxxxx>
---
 drivers/block/xen-blkback/common.h | 7 ++++---
 drivers/block/xen-blkback/xenbus.c | 2 +-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/block/xen-blkback/common.h 
b/drivers/block/xen-blkback/common.h
index 1d3002d773f7..9db5f3586fb4 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -35,6 +35,7 @@
 #include <linux/wait.h>
 #include <linux/io.h>
 #include <linux/rbtree.h>
+#include <linux/refcount.h>
 #include <asm/setup.h>
 #include <asm/pgalloc.h>
 #include <asm/hypervisor.h>
@@ -309,7 +310,7 @@ struct xen_blkif {
        struct xen_vbd          vbd;
        /* Back pointer to the backend_info. */
        struct backend_info     *be;
-       atomic_t                refcnt;
+       refcount_t              refcnt;
        /* for barrier (drain) requests */
        struct completion       drain_complete;
        atomic_t                drain;
@@ -362,10 +363,10 @@ struct pending_req {
                         (_v)->bdev->bd_part->nr_sects : \
                          get_capacity((_v)->bdev->bd_disk))
 
-#define xen_blkif_get(_b) (atomic_inc(&(_b)->refcnt))
+#define xen_blkif_get(_b) (refcount_inc(&(_b)->refcnt))
 #define xen_blkif_put(_b)                              \
        do {                                            \
-               if (atomic_dec_and_test(&(_b)->refcnt)) \
+               if (refcount_dec_and_test(&(_b)->refcnt))       \
                        schedule_work(&(_b)->free_work);\
        } while (0)
 
diff --git a/drivers/block/xen-blkback/xenbus.c 
b/drivers/block/xen-blkback/xenbus.c
index 3ac6a5d18071..ecc5f9c5bf3f 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -169,7 +169,7 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
                return ERR_PTR(-ENOMEM);
 
        blkif->domid = domid;
-       atomic_set(&blkif->refcnt, 1);
+       refcount_set(&blkif->refcnt, 1);
        init_completion(&blkif->drain_complete);
        INIT_WORK(&blkif->free_work, xen_blkif_deferred_free);
 
-- 
2.20.1


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