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

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Date:   Tue, 9 Jul 2019 16:10:24 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.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 Tue, Jul 09, 2019 at 03:44:59PM -0700, Nick Desaulniers wrote:
> 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

I assume that the reason for this is there may be other cipher types
added in the future? I suppose the maintainers can give more clarity to
that.

Furthermore, if they want the switch statements to remain, it looks like
fill_static_params_ctx also returns in the default statement so it seems
like this is the right fix.

Cheers,
Nathan