[Xen-devel] [PATCH v2 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>
---
Changes in v2:
  - Also convert pending_req::pendcnt to refcount_t.

 drivers/block/xen-blkback/blkback.c | 6 +++---
 drivers/block/xen-blkback/common.h  | 9 +++++----
 drivers/block/xen-blkback/xenbus.c  | 2 +-
 3 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/drivers/block/xen-blkback/blkback.c 
b/drivers/block/xen-blkback/blkback.c
index fd1e19f1a49f..b24bb0aea35f 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -1098,7 +1098,7 @@ static void __end_block_io_op(struct pending_req 
*pending_req,
         * the grant references associated with 'request' and provide
         * the proper response on the ring.
         */
-       if (atomic_dec_and_test(&pending_req->pendcnt))
+       if (refcount_dec_and_test(&pending_req->pendcnt))
                xen_blkbk_unmap_and_respond(pending_req);
 }
 
@@ -1395,7 +1395,7 @@ static int dispatch_rw_block_io(struct xen_blkif_ring 
*ring,
                bio_set_op_attrs(bio, operation, operation_flags);
        }
 
-       atomic_set(&pending_req->pendcnt, nbio);
+       refcount_set(&pending_req->pendcnt, nbio);
        blk_start_plug(&plug);
 
        for (i = 0; i < nbio; i++)
@@ -1424,7 +1424,7 @@ static int dispatch_rw_block_io(struct xen_blkif_ring 
*ring,
  fail_put_bio:
        for (i = 0; i < nbio; i++)
                bio_put(biolist[i]);
-       atomic_set(&pending_req->pendcnt, 1);
+       refcount_set(&pending_req->pendcnt, 1);
        __end_block_io_op(pending_req, BLK_STS_RESOURCE);
        msleep(1); /* back off a bit */
        return -EIO;
diff --git a/drivers/block/xen-blkback/common.h 
b/drivers/block/xen-blkback/common.h
index 1d3002d773f7..824d64a8339b 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;
@@ -343,7 +344,7 @@ struct pending_req {
        struct xen_blkif_ring   *ring;
        u64                     id;
        int                     nr_segs;
-       atomic_t                pendcnt;
+       refcount_t              pendcnt;
        unsigned short          operation;
        int                     status;
        struct list_head        free_list;
@@ -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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