[PATCH] scsi: libfc: Use refcount_* APIs for reference count management

[Deepak R Varma]

The atomic_t API based object reference counter management is prone to
counter value overflows, object use-after-free issues and to return
puzzling values. The improved refcount_t APIs are designed to address
these known issues with atomic_t reference counter management. This
white paper [1] has detailed reasons for moving from atomic_t to
refcount_t APIs. Hence replace the atomic_* based implementation by its
refcount_* based equivalent.
The issue is identified using atomic_as_refcounter.cocci Coccinelle
semantic patch script.

	[1] https://arxiv.org/pdf/1710.06175.pdf

Signed-off-by: Deepak R Varma <drv@xxxxxxxxx>
---
Note: The proposal is compile tested only.

 drivers/scsi/libfc/fc_exch.c | 10 +++++-----
 include/scsi/libfc.h         |  2 +-
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/scsi/libfc/fc_exch.c b/drivers/scsi/libfc/fc_exch.c
index 1d91c457527f..1c49fddb65e3 100644
--- a/drivers/scsi/libfc/fc_exch.c
+++ b/drivers/scsi/libfc/fc_exch.c
@@ -246,7 +246,7 @@ static const char *fc_exch_rctl_name(unsigned int op)
  */
 static inline void fc_exch_hold(struct fc_exch *ep)
 {
-	atomic_inc(&ep->ex_refcnt);
+	refcount_inc(&ep->ex_refcnt);
 }

 /**
@@ -312,7 +312,7 @@ static void fc_exch_release(struct fc_exch *ep)
 {
 	struct fc_exch_mgr *mp;

-	if (atomic_dec_and_test(&ep->ex_refcnt)) {
+	if (refcount_dec_and_test(&ep->ex_refcnt)) {
 		mp = ep->em;
 		if (ep->destructor)
 			ep->destructor(&ep->seq, ep->arg);
@@ -329,7 +329,7 @@ static inline void fc_exch_timer_cancel(struct fc_exch *ep)
 {
 	if (cancel_delayed_work(&ep->timeout_work)) {
 		FC_EXCH_DBG(ep, "Exchange timer canceled\n");
-		atomic_dec(&ep->ex_refcnt); /* drop hold for timer */
+		refcount_dec(&ep->ex_refcnt); /* drop hold for timer */
 	}
 }

@@ -1897,7 +1897,7 @@ static void fc_exch_reset(struct fc_exch *ep)
 	ep->state |= FC_EX_RST_CLEANUP;
 	fc_exch_timer_cancel(ep);
 	if (ep->esb_stat & ESB_ST_REC_QUAL)
-		atomic_dec(&ep->ex_refcnt);	/* drop hold for rec_qual */
+		refcount_dec(&ep->ex_refcnt);	/* drop hold for rec_qual */
 	ep->esb_stat &= ~ESB_ST_REC_QUAL;
 	sp = &ep->seq;
 	rc = fc_exch_done_locked(ep);
@@ -2332,7 +2332,7 @@ static void fc_exch_els_rrq(struct fc_frame *fp)
 	 */
 	if (ep->esb_stat & ESB_ST_REC_QUAL) {
 		ep->esb_stat &= ~ESB_ST_REC_QUAL;
-		atomic_dec(&ep->ex_refcnt);	/* drop hold for rec qual */
+		refcount_dec(&ep->ex_refcnt);	/* drop hold for rec qual */
 	}
 	if (ep->esb_stat & ESB_ST_COMPLETE)
 		fc_exch_timer_cancel(ep);
diff --git a/include/scsi/libfc.h b/include/scsi/libfc.h
index 6e29e1719db1..ce65149b300c 100644
--- a/include/scsi/libfc.h
+++ b/include/scsi/libfc.h
@@ -432,7 +432,7 @@ struct fc_seq {
  */
 struct fc_exch {
 	spinlock_t	    ex_lock;
-	atomic_t	    ex_refcnt;
+	refcount_t	    ex_refcnt;
 	enum fc_class	    class;
 	struct fc_exch_mgr  *em;
 	struct fc_exch_pool *pool;
--
2.34.1