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From:   Arnd Bergmann <arnd@kernel.org>
To:     Saeed Mahameed <saeedm@nvidia.com>,
        Leon Romanovsky <leon@kernel.org>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, Tariq Toukan <tariqt@nvidia.com>,
        Maxim Mikityanskiy <maximmi@nvidia.com>,
        Gal Pressman <gal@nvidia.com>, Lama Kayal <lkayal@nvidia.com>,
        Moshe Tal <moshet@nvidia.com>, netdev@vger.kernel.org,
        linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev
Subject: [PATCH] [v2] mlx5: reduce stack usage in mlx5_setup_tc
Date:   Tue, 17 Jan 2023 22:01:55 +0100
Message-Id: <20230117210324.1371169-1-arnd@kernel.org>
MIME-Version: 1.0
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From: Arnd Bergmann <arnd@arndb.de>

Clang warns about excessive stack usage on 32-bit targets:

drivers/net/ethernet/mellanox/mlx5/core/en_main.c:3597:12: error: stack frame size (1184) exceeds limit (1024) in 'mlx5e_setup_tc' [-Werror,-Wframe-larger-than]
static int mlx5e_setup_tc(struct net_device *dev, enum tc_setup_type type,

It turns out that both the mlx5e_setup_tc_mqprio_dcb() function and
the mlx5e_safe_switch_params() function it calls have a copy of
'struct mlx5e_params' on the stack, and this structure is fairly
large.

Use dynamic allocation for the inner one.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
v2: simplify the patch
---
 .../net/ethernet/mellanox/mlx5/core/en_main.c   | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
index 6bb0fdaa5efa..b0b872728653 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
@@ -2998,32 +2998,37 @@ int mlx5e_safe_switch_params(struct mlx5e_priv *priv,
 			     mlx5e_fp_preactivate preactivate,
 			     void *context, bool reset)
 {
-	struct mlx5e_channels new_chs = {};
+	struct mlx5e_channels *new_chs;
 	int err;
 
 	reset &= test_bit(MLX5E_STATE_OPENED, &priv->state);
 	if (!reset)
 		return mlx5e_switch_priv_params(priv, params, preactivate, context);
 
-	new_chs.params = *params;
+	new_chs = kzalloc(sizeof(*new_chs), GFP_KERNEL);
+	if (!new_chs)
+		return -ENOMEM;
+	new_chs->params = *params;
 
-	mlx5e_selq_prepare_params(&priv->selq, &new_chs.params);
+	mlx5e_selq_prepare_params(&priv->selq, &new_chs->params);
 
-	err = mlx5e_open_channels(priv, &new_chs);
+	err = mlx5e_open_channels(priv, new_chs);
 	if (err)
 		goto err_cancel_selq;
 
-	err = mlx5e_switch_priv_channels(priv, &new_chs, preactivate, context);
+	err = mlx5e_switch_priv_channels(priv, new_chs, preactivate, context);
 	if (err)
 		goto err_close;
 
+	kfree(new_chs);
 	return 0;
 
 err_close:
-	mlx5e_close_channels(&new_chs);
+	mlx5e_close_channels(new_chs);
 
 err_cancel_selq:
 	mlx5e_selq_cancel(&priv->selq);
+	kfree(new_chs);
 	return err;
 }
 
-- 
2.39.0