[PATCH 1/2] net/mlx5e: shut up maybe-uninitialized warning

Build-testing this driver with -Wmaybe-uninitialized gives a new false-positive
warning that I can't really explain:

drivers/net/ethernet/mellanox/mlx5/core/en_tc.c: In function 'mlx5e_configure_flower':
drivers/net/ethernet/mellanox/mlx5/core/en_tc.c:509:3: error: 'old_attr' may be used uninitialized in this function [-Werror=maybe-uninitialized]

It's obvious from the code that 'old_attr' is initialized whenever 'old'
is non-NULL here. The warning appears with all versions I tested from gcc-4.7
through gcc-6.1, and I could not come up with a way to rewrite the function
in a more readable way that avoids the warning, so I'm adding another
initialization to shut it up.

Fixes: 8b32580df1cb ("net/mlx5e: Add TC vlan action for SRIOV offloads")
Signed-off-by: Arnd Bergmann <redacted>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_tc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_tc.c b/drivers/net/ethernet/mellanox/mlx5/core/en_tc.c
index a350b7171e3d..ce8c54d18906 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_tc.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_tc.c

@@ -451,7 +451,7 @@ int mlx5e_configure_flower(struct mlx5e_priv *priv, __be16 protocol,
 	struct mlx5e_tc_flow *flow;
 	struct mlx5_flow_spec *spec;
 	struct mlx5_flow_rule *old = NULL;
-	struct mlx5_esw_flow_attr *old_attr;
+	struct mlx5_esw_flow_attr *old_attr = NULL;
 	struct mlx5_eswitch *esw = priv->mdev->priv.eswitch;
 
 	if (esw && esw->mode == SRIOV_OFFLOADS)

-- 
2.9.0

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If fi->fib_nhs is zero, the router interface pointer is uninitialized, as shown by
this warning:

drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c: In function 'mlxsw_sp_router_fib_event':
drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:1674:21: error: 'r' may be used uninitialized in this function [-Werror=maybe-uninitialized]
drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:1643:23: note: 'r' was declared here

This changes the loop so we handle the case the same way as finding no router
interface pointer attached to one of the nexthops to ensure we always
trap here instead of using uninitialized data.

Fixes: b45f64d16d45 ("mlxsw: spectrum_router: Use FIB notifications instead of switchdev calls")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
index 48d50efec5e2..78fc557d6dd7 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c

@@ -1640,7 +1640,7 @@ mlxsw_sp_router_fib4_entry_init(struct mlxsw_sp *mlxsw_sp,
 				struct mlxsw_sp_fib_entry *fib_entry)
 {
 	struct fib_info *fi = fen_info->fi;
-	struct mlxsw_sp_rif *r;
+	struct mlxsw_sp_rif *r = NULL;
 	int nhsel;
 	int err;
 

@@ -1664,11 +1664,15 @@ mlxsw_sp_router_fib4_entry_init(struct mlxsw_sp *mlxsw_sp,
 			 * to us. Set trap and pass the packets for
 			 * this prefix to kernel.
 			 */
-			fib_entry->type = MLXSW_SP_FIB_ENTRY_TYPE_TRAP;
-			return 0;
+			break;
 		}
 	}
 
+	if (!r) {
+		fib_entry->type = MLXSW_SP_FIB_ENTRY_TYPE_TRAP;
+		return 0;
+	}
+
 	if (fi->fib_scope != RT_SCOPE_UNIVERSE) {
 		fib_entry->type = MLXSW_SP_FIB_ENTRY_TYPE_LOCAL;
 		fib_entry->rif = r->rif;

-- 
2.9.0

On Fri, Sep 30, 2016 at 06:17:10PM +0200, Arnd Bergmann wrote:

If fi->fib_nhs is zero, the router interface pointer is uninitialized, as shown by
this warning:

drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c: In function 'mlxsw_sp_router_fib_event':
drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:1674:21: error: 'r' may be used uninitialized in this function [-Werror=maybe-uninitialized]
drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:1643:23: note: 'r' was declared here

This changes the loop so we handle the case the same way as finding no router
interface pointer attached to one of the nexthops to ensure we always
trap here instead of using uninitialized data.

Fixes: b45f64d16d45 ("mlxsw: spectrum_router: Use FIB notifications instead of switchdev calls")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

For net-next:
Acked-by: Ido Schimmel <redacted>

BTW, which flags did you pass to generate this error? I can only
reproduce this with EXTRA_CFLAGS="-Wmaybe-uninitialized -Werror", but
for some reason EXTRA_CFLAGS="-Wall -Werror" is silent. Any idea why? I
would like to add this to my git hooks and avoid these errors in the
future :)

Thanks!

On Friday 30 September 2016, Ido Schimmel wrote:

BTW, which flags did you pass to generate this error? I can only
reproduce this with EXTRA_CFLAGS="-Wmaybe-uninitialized -Werror", but
for some reason EXTRA_CFLAGS="-Wall -Werror" is silent. Any idea why? I
would like to add this to my git hooks and avoid these errors in the
future :)

Linus disabled the warning for v4.8. I've just talked to him today about this
warning in particular, and hope that we can find a way to enable it by
default again in the future, as a lot of possible bugs get introduced,
but certain compiler versions also produce a lot of false positives.

	Arnd

On Fri, Sep 30, 2016 at 7:17 PM, Arnd Bergmann [off-list ref] wrote:

Build-testing this driver with -Wmaybe-uninitialized gives a new false-positive
warning that I can't really explain:

drivers/net/ethernet/mellanox/mlx5/core/en_tc.c: In function 'mlx5e_configure_flower':
drivers/net/ethernet/mellanox/mlx5/core/en_tc.c:509:3: error: 'old_attr' may be used uninitialized in this function [-Werror=maybe-uninitialized]

It's obvious from the code that 'old_attr' is initialized whenever 'old'
is non-NULL here. The warning appears with all versions I tested from gcc-4.7
through gcc-6.1, and I could not come up with a way to rewrite the function
in a more readable way that avoids the warning, so I'm adding another
initialization to shut it up.

Fixes: 8b32580df1cb ("net/mlx5e: Add TC vlan action for SRIOV offloads")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Yeah, this is clearly false positive and I was sure that newish GCCs
don't show that, but you are the master here.. so FWIW

Acked-by: Or Gerlitz <redacted>

From: Arnd Bergmann <redacted>
Date: Fri, 30 Sep 2016 18:17:09 +0200

Build-testing this driver with -Wmaybe-uninitialized gives a new false-positive
warning that I can't really explain:

drivers/net/ethernet/mellanox/mlx5/core/en_tc.c: In function 'mlx5e_configure_flower':
drivers/net/ethernet/mellanox/mlx5/core/en_tc.c:509:3: error: 'old_attr' may be used uninitialized in this function [-Werror=maybe-uninitialized]

It's obvious from the code that 'old_attr' is initialized whenever 'old'
is non-NULL here. The warning appears with all versions I tested from gcc-4.7
through gcc-6.1, and I could not come up with a way to rewrite the function
in a more readable way that avoids the warning, so I'm adding another
initialization to shut it up.

Fixes: 8b32580df1cb ("net/mlx5e: Add TC vlan action for SRIOV offloads")
Signed-off-by: Arnd Bergmann <redacted>

Applied.
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From: Arnd Bergmann <arnd@arndb.de>
Date: Fri, 30 Sep 2016 18:17:10 +0200

If fi->fib_nhs is zero, the router interface pointer is uninitialized, as shown by
this warning:

drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c: In function 'mlxsw_sp_router_fib_event':
drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:1674:21: error: 'r' may be used uninitialized in this function [-Werror=maybe-uninitialized]
drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:1643:23: note: 'r' was declared here

This changes the loop so we handle the case the same way as finding no router
interface pointer attached to one of the nexthops to ensure we always
trap here instead of using uninitialized data.

Fixes: b45f64d16d45 ("mlxsw: spectrum_router: Use FIB notifications instead of switchdev calls")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Applied.