[PATCH] xfs: Convert from atomic_t to refcount_t on xlog_ticket->t_ref

[Xiyu Yang]

refcount_t type and corresponding API can protect refcounters from
accidental underflow and overflow and further use-after-free situations.

Signed-off-by: Xiyu Yang <xiyuyang19@xxxxxxxxxxxx>
Signed-off-by: Xin Tan <tanxin.ctf@xxxxxxxxx>
---
 fs/xfs/xfs_log.c      | 10 +++++-----
 fs/xfs/xfs_log_priv.h |  4 +++-
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 36fa2650b081..1da711f1a229 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -3347,8 +3347,8 @@ void
 xfs_log_ticket_put(
 	xlog_ticket_t	*ticket)
 {
-	ASSERT(atomic_read(&ticket->t_ref) > 0);
-	if (atomic_dec_and_test(&ticket->t_ref))
+	ASSERT(refcount_read(&ticket->t_ref) > 0);
+	if (refcount_dec_and_test(&ticket->t_ref))
 		kmem_cache_free(xfs_log_ticket_zone, ticket);
 }
 
@@ -3356,8 +3356,8 @@ xlog_ticket_t *
 xfs_log_ticket_get(
 	xlog_ticket_t	*ticket)
 {
-	ASSERT(atomic_read(&ticket->t_ref) > 0);
-	atomic_inc(&ticket->t_ref);
+	ASSERT(refcount_read(&ticket->t_ref) > 0);
+	refcount_inc(&ticket->t_ref);
 	return ticket;
 }
 
@@ -3477,7 +3477,7 @@ xlog_ticket_alloc(
 
 	unit_res = xlog_calc_unit_res(log, unit_bytes);
 
-	atomic_set(&tic->t_ref, 1);
+	refcount_set(&tic->t_ref, 1);
 	tic->t_task		= current;
 	INIT_LIST_HEAD(&tic->t_queue);
 	tic->t_unit_res		= unit_res;
diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
index 4c41bbfa33b0..c4157d87cea4 100644
--- a/fs/xfs/xfs_log_priv.h
+++ b/fs/xfs/xfs_log_priv.h
@@ -6,6 +6,8 @@
 #ifndef	__XFS_LOG_PRIV_H__
 #define __XFS_LOG_PRIV_H__
 
+#include <linux/refcount.h>
+
 struct xfs_buf;
 struct xlog;
 struct xlog_ticket;
@@ -163,7 +165,7 @@ typedef struct xlog_ticket {
 	struct list_head   t_queue;	 /* reserve/write queue */
 	struct task_struct *t_task;	 /* task that owns this ticket */
 	xlog_tid_t	   t_tid;	 /* transaction identifier	 : 4  */
-	atomic_t	   t_ref;	 /* ticket reference count       : 4  */
+	refcount_t	   t_ref;	 /* ticket reference count       : 4  */
 	int		   t_curr_res;	 /* current reservation in bytes : 4  */
 	int		   t_unit_res;	 /* unit reservation in bytes    : 4  */
 	char		   t_ocnt;	 /* original count		 : 1  */
-- 
2.7.4