locking/atomic, kref: Add kref_read()

Since we need to change the implementation, stop exposing internals.

Provide kref_read() to read the current reference count; typically
used for debug messages.

Kills two anti-patterns:

	atomic_read(&kref->refcount)
	kref->refcount.counter

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/drivers/target/target_core_pr.c b/drivers/target/target_core_pr.c
index d761025..e180511 100644
--- a/drivers/target/target_core_pr.c
+++ b/drivers/target/target_core_pr.c
@@ -788,7 +788,7 @@ static struct t10_pr_registration *__core_scsi3_alloc_registration(
 			 * __core_scsi3_add_registration()
 			 */
 			dest_lun = rcu_dereference_check(deve_tmp->se_lun,
-				atomic_read(&deve_tmp->pr_kref.refcount) != 0);
+				kref_read(&deve_tmp->pr_kref) != 0);
 
 			pr_reg_atp = __core_scsi3_do_alloc_registration(dev,
 						nacl_tmp, dest_lun, deve_tmp,
@@ -1463,7 +1463,7 @@ static int core_scsi3_lunacl_depend_item(struct se_dev_entry *se_deve)
 	 * For nacl->dynamic_node_acl=1
 	 */
 	lun_acl = rcu_dereference_check(se_deve->se_lun_acl,
-				atomic_read(&se_deve->pr_kref.refcount) != 0);
+				kref_read(&se_deve->pr_kref) != 0);
 	if (!lun_acl)
 		return 0;
 
@@ -1478,7 +1478,7 @@ static void core_scsi3_lunacl_undepend_item(struct se_dev_entry *se_deve)
 	 * For nacl->dynamic_node_acl=1
 	 */
 	lun_acl = rcu_dereference_check(se_deve->se_lun_acl,
-				atomic_read(&se_deve->pr_kref.refcount) != 0);
+				kref_read(&se_deve->pr_kref) != 0);
 	if (!lun_acl) {
 		kref_put(&se_deve->pr_kref, target_pr_kref_release);
 		return;
@@ -1759,7 +1759,7 @@ core_scsi3_decode_spec_i_port(
 		 * 2nd loop which will never fail.
 		 */
 		dest_lun = rcu_dereference_check(dest_se_deve->se_lun,
-				atomic_read(&dest_se_deve->pr_kref.refcount) != 0);
+				kref_read(&dest_se_deve->pr_kref) != 0);
 
 		dest_pr_reg = __core_scsi3_alloc_registration(cmd->se_dev,
 					dest_node_acl, dest_lun, dest_se_deve,
@@ -3466,7 +3466,7 @@ core_scsi3_emulate_pro_register_and_move(struct se_cmd *cmd, u64 res_key,
 					iport_ptr);
 	if (!dest_pr_reg) {
 		struct se_lun *dest_lun = rcu_dereference_check(dest_se_deve->se_lun,
-				atomic_read(&dest_se_deve->pr_kref.refcount) != 0);
+				kref_read(&dest_se_deve->pr_kref) != 0);
 
 		spin_unlock(&dev->dev_reservation_lock);
 		if (core_scsi3_alloc_registration(cmd->se_dev, dest_node_acl,