scsi: hisi_sas: add memory barrier in task delivery function

In task start delivery function, we need to add a memory barrier to prevent
re-ordering of reading memory by hardware. Because the slot data is set in
task prepare function and it could be running in another CPU.

This patch adds an memory barrier after s->ready is read in the task start
delivery function, and uses WRITE_ONCE() in the places where s->ready is
set to ensure that the compiler does not re-order.

Signed-off-by: Xiaofei Tan <tanxiaofei@huawei.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/drivers/scsi/hisi_sas/hisi_sas_v1_hw.c b/drivers/scsi/hisi_sas/hisi_sas_v1_hw.c
index 7dc68740eac9..8f60f0e04599 100644
--- a/drivers/scsi/hisi_sas/hisi_sas_v1_hw.c
+++ b/drivers/scsi/hisi_sas/hisi_sas_v1_hw.c
@@ -903,23 +903,28 @@ get_free_slot_v1_hw(struct hisi_hba *hisi_hba, struct hisi_sas_dq *dq)
 static void start_delivery_v1_hw(struct hisi_sas_dq *dq)
 {
 	struct hisi_hba *hisi_hba = dq->hisi_hba;
-	struct hisi_sas_slot *s, *s1;
+	struct hisi_sas_slot *s, *s1, *s2 = NULL;
 	struct list_head *dq_list;
 	int dlvry_queue = dq->id;
-	int wp, count = 0;
+	int wp;
 
 	dq_list = &dq->list;
 	list_for_each_entry_safe(s, s1, &dq->list, delivery) {
 		if (!s->ready)
 			break;
-		count++;
-		wp = (s->dlvry_queue_slot + 1) % HISI_SAS_QUEUE_SLOTS;
+		s2 = s;
 		list_del(&s->delivery);
 	}
 
-	if (!count)
+	if (!s2)
 		return;
 
+	/*
+	 * Ensure that memories for slots built on other CPUs is observed.
+	 */
+	smp_rmb();
+	wp = (s2->dlvry_queue_slot + 1) % HISI_SAS_QUEUE_SLOTS;
+
 	hisi_sas_write32(hisi_hba, DLVRY_Q_0_WR_PTR + (dlvry_queue * 0x14), wp);
 }