netdev - [PATCH v3 net-next 7/7] qed: Fix possible race when reading firmware return code.

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Date:   Fri, 14 Oct 2016 05:19:23 -0400
From:   Manish Chopra <manish.chopra@...gic.com>
To:     <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>, <Yuval.Mintz@...gic.com>,
        Manish Chopra <manish.chopra@...iumnetworks.com>
Subject: [PATCH v3 net-next 7/7] qed: Fix possible race when reading firmware return code.

From: Manish Chopra <manish.chopra@...iumnetworks.com>

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@...iumnetworks.com>
Signed-off-by: Yuval Mintz <Yuval.Mintz@...iumnetworks.com>
---
 drivers/net/ethernet/qlogic/qed/qed_sp.h  |  4 ++--
 drivers/net/ethernet/qlogic/qed/qed_spq.c | 12 ++++++------
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/qlogic/qed/qed_sp.h b/drivers/net/ethernet/qlogic/qed/qed_sp.h
index 652c908..27c450f 100644
--- a/drivers/net/ethernet/qlogic/qed/qed_sp.h
+++ b/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 {
diff --git a/drivers/net/ethernet/qlogic/qed/qed_spq.c b/drivers/net/ethernet/qlogic/qed/qed_spq.c
index 259a615..6c05402 100644
--- a/drivers/net/ethernet/qlogic/qed/qed_spq.c
+++ b/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;
-- 
2.7.2