linux-kernel - [PATCH 3.2 113/147] IB/mlx4: Fix compiler warning about uninitialized 'vlan' variable

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Message-ID: <lsq.1510009387.583675093@decadent.org.uk>
Date:   Mon, 06 Nov 2017 23:03:07 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Paul Bolle" <pebolle@...cali.nl>,
        "Roland Dreier" <roland@...estorage.com>
Subject: [PATCH 3.2 113/147] IB/mlx4: Fix compiler warning about
 uninitialized 'vlan' variable

3.2.95-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Paul Bolle <pebolle@...cali.nl>

commit 57d88cffc83a2120266bbe9e72cbba5bd5f33675 upstream.

Building qp.o triggers this gcc warning:

    drivers/infiniband/hw/mlx4/qp.c: In function ‘mlx4_ib_post_send’:
    drivers/infiniband/hw/mlx4/qp.c:1862:62: warning: ‘vlan’ may be used uninitialized in this function [-Wmaybe-uninitialized]
    drivers/infiniband/hw/mlx4/qp.c:1752:6: note: ‘vlan’ was declared here

Looking at the code it is clear 'vlan' is only set and used if 'is_eth'
is non-zero. But by initializing 'vlan' to 0xffff, on

    gcc (Ubuntu 4.7.2-22ubuntu1) 4.7.2

on x86-64 at least, we fix the warning, and the compiler was already
setting 'vlan' to 0 in the generated code, so there's no real downside.

Signed-off-by: Paul Bolle <pebolle@...cali.nl>

[ Get rid of unnecessary move of 'is_vlan' initialization.  - Roland ]

Signed-off-by: Roland Dreier <roland@...estorage.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/infiniband/hw/mlx4/qp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/infiniband/hw/mlx4/qp.c
+++ b/drivers/infiniband/hw/mlx4/qp.c
@@ -1363,7 +1363,7 @@ static int build_mlx_header(struct mlx4_
 	int is_eth;
 	int is_vlan = 0;
 	int is_grh;
-	u16 vlan;
+	u16 vlan = 0xffff;
 
 	send_size = 0;
 	for (i = 0; i < wr->num_sge; ++i)