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>
diff --git a/drivers/target/loopback/tcm_loop.c b/drivers/target/loopback/tcm_loop.c
index 340de9d..a7f6dc6 100644
--- a/drivers/target/loopback/tcm_loop.c
+++ b/drivers/target/loopback/tcm_loop.c
@@ -960,8 +960,7 @@
struct tcm_loop_tpg, tl_se_tpg);
struct tcm_loop_hba *tl_hba = tl_tpg->tl_hba;
- atomic_inc(&tl_tpg->tl_tpg_port_count);
- smp_mb__after_atomic();
+ atomic_inc_mb(&tl_tpg->tl_tpg_port_count);
/*
* Add Linux/SCSI struct scsi_device by HCTL
*/
@@ -995,8 +994,7 @@
scsi_remove_device(sd);
scsi_device_put(sd);
- atomic_dec(&tl_tpg->tl_tpg_port_count);
- smp_mb__after_atomic();
+ atomic_dec_mb(&tl_tpg->tl_tpg_port_count);
pr_debug("TCM_Loop_ConfigFS: Port Unlink Successful\n");
}