linux-kernel - Re: [PATCH] net/mlx5e: Return in default case statement in tx_post_resync

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Message-ID: <CAKwvOdkYdNiKorJAKHZ7LTfk9eOpMqe6F4QSmJWQ=-YNuPAyrw@mail.gmail.com>
Date:   Tue, 9 Jul 2019 15:44:59 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Saeed Mahameed <saeedm@...lanox.com>,
        Leon Romanovsky <leon@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Boris Pismenny <borisp@...lanox.com>, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] net/mlx5e: Return in default case statement in tx_post_resync_params

On Mon, Jul 8, 2019 at 4:13 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> clang warns:
>
> drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c:251:2:
> warning: variable 'rec_seq_sz' is used uninitialized whenever switch
> default is taken [-Wsometimes-uninitialized]
>         default:
>         ^~~~~~~
> drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c:255:46: note:
> uninitialized use occurs here
>         skip_static_post = !memcmp(rec_seq, &rn_be, rec_seq_sz);
>                                                     ^~~~~~~~~~
> drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c:239:16: note:
> initialize the variable 'rec_seq_sz' to silence this warning
>         u16 rec_seq_sz;
>                       ^
>                        = 0
> 1 warning generated.
>
> This case statement was clearly designed to be one that should not be
> hit during runtime because of the WARN_ON statement so just return early
> to prevent copying uninitialized memory up into rn_be.
>
> Fixes: d2ead1f360e8 ("net/mlx5e: Add kTLS TX HW offload support")
> Link: https://github.com/ClangBuiltLinux/linux/issues/590
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c
> index 3f5f4317a22b..5c08891806f0 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c
> @@ -250,6 +250,7 @@ tx_post_resync_params(struct mlx5e_txqsq *sq,
>         }
>         default:
>                 WARN_ON(1);
> +               return;
>         }

hmm...a switch statement with a single case is a code smell.  How
about a single conditional with early return?  Then the "meat" of the
happy path doesn't need an additional level of indentation.
-- 
Thanks,
~Nick Desaulniers