target: encapsulate smp_mb__after_atomic()

The target code has a rather generous helping of smp_mb__after_atomic()
throughout the code base.  Most atomic operations were followed by one
and none were preceded by smp_mb__before_atomic(), nor accompanied by a
comment explaining the need for a barrier.

Instead of trying to prove for every case whether or not it is needed,
this patch introduces atomic_inc_mb() and atomic_dec_mb(), which
explicitly include the memory barriers before and after the atomic
operation.  For now they are defined in a target header, although they
could be of general use.

Most of the existing atomic/mb combinations were replaced by the new
helpers.  In a few cases the atomic was sandwiched in
spin_lock/spin_unlock and I simply removed the barrier.

I suspect that in most cases the correct conversion would have been to
drop the barrier.  I also suspect that a few cases exist where a) the
barrier was necessary and b) a second barrier before the atomic would
have been necessary and got added by this patch.

Signed-off-by: Joern Engel <joern@logfs.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 5 insertions, 10 deletions

diff --git a/drivers/target/target_core_ua.c b/drivers/target/target_core_ua.c
index 101858e245b3..1738b1646988 100644
--- a/drivers/target/target_core_ua.c
+++ b/drivers/target/target_core_ua.c
@@ -161,8 +161,7 @@ int core_scsi3_ua_allocate(
 		spin_unlock(&deve->ua_lock);
 		spin_unlock_irq(&nacl->device_list_lock);
 
-		atomic_inc(&deve->ua_count);
-		smp_mb__after_atomic();
+		atomic_inc_mb(&deve->ua_count);
 		return 0;
 	}
 	list_add_tail(&ua->ua_nacl_list, &deve->ua_list);
@@ -174,8 +173,7 @@ int core_scsi3_ua_allocate(
 		nacl->se_tpg->se_tpg_tfo->get_fabric_name(), unpacked_lun,
 		asc, ascq);
 
-	atomic_inc(&deve->ua_count);
-	smp_mb__after_atomic();
+	atomic_inc_mb(&deve->ua_count);
 	return 0;
 }
 
@@ -189,8 +187,7 @@ void core_scsi3_ua_release_all(
 		list_del(&ua->ua_nacl_list);
 		kmem_cache_free(se_ua_cache, ua);
 
-		atomic_dec(&deve->ua_count);
-		smp_mb__after_atomic();
+		atomic_dec_mb(&deve->ua_count);
 	}
 	spin_unlock(&deve->ua_lock);
 }
@@ -250,8 +247,7 @@ void core_scsi3_ua_for_check_condition(
 		list_del(&ua->ua_nacl_list);
 		kmem_cache_free(se_ua_cache, ua);
 
-		atomic_dec(&deve->ua_count);
-		smp_mb__after_atomic();
+		atomic_dec_mb(&deve->ua_count);
 	}
 	spin_unlock(&deve->ua_lock);
 	spin_unlock_irq(&nacl->device_list_lock);
@@ -309,8 +305,7 @@ int core_scsi3_ua_clear_for_request_sense(
 		list_del(&ua->ua_nacl_list);
 		kmem_cache_free(se_ua_cache, ua);
 
-		atomic_dec(&deve->ua_count);
-		smp_mb__after_atomic();
+		atomic_dec_mb(&deve->ua_count);
 	}
 	spin_unlock(&deve->ua_lock);
 	spin_unlock_irq(&nacl->device_list_lock);