qed: Fix possible race when reading firmware return code.

While handling SPQ ramrod completion, there is a possible race
where driver might not read updated fw return code based on
ramrod completion done. This patch ensures that fw return code
is written first and then completion done flag is updated
using appropriate memory barriers.

Signed-off-by: Manish Chopra <manish.chopra@caviumnetworks.com>
Signed-off-by: Yuval Mintz <Yuval.Mintz@caviumnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/qlogic/qed/qed_sp.h

@@ -111,8 +111,8 @@ union qed_spq_req_comp {
 };
 
 struct qed_spq_comp_done {
-	u64	done;
-	u8	fw_return_code;
+	unsigned int	done;
+	u8		fw_return_code;
 };
 
 struct qed_spq_entry {

drivers/net/ethernet/qlogic/qed/qed_spq.c

@@ -54,11 +54,10 @@ static void qed_spq_blocking_cb(struct qed_hwfn *p_hwfn,
 
 	comp_done = (struct qed_spq_comp_done *)cookie;
 
-	comp_done->done			= 0x1;
-	comp_done->fw_return_code	= fw_return_code;
+	comp_done->fw_return_code = fw_return_code;
 
-	/* make update visible to waiting thread */
-	smp_wmb();
+	/* Make sure completion done is visible on waiting thread */
+	smp_store_release(&comp_done->done, 0x1);
 }
 
 static int __qed_spq_block(struct qed_hwfn *p_hwfn,
@@ -74,8 +73,9 @@ static int __qed_spq_block(struct qed_hwfn *p_hwfn,
 
 	while (iter_cnt--) {
 		/* Validate we receive completion update */
-		smp_rmb();
-		if (comp_done->done == 1) {
+		if (READ_ONCE(comp_done->done) == 1) {
+			/* Read updated FW return value */
+			smp_read_barrier_depends();
 			if (p_fw_ret)
 				*p_fw_ret = comp_done->fw_return_code;
 			return 0;