linux-kernel - Re: [PATCH] chelsio: use BUG() instead of BUG

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Message-ID: <CAKwvOdkLmJaDH8XdCQBJkiFztme3_c7-AE+Z47imkdYA0n4ShQ@mail.gmail.com>
Date:   Mon, 25 Mar 2019 10:31:10 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Vishal Kulkarni <vishal@...lsio.com>,
        "David S. Miller" <davem@...emloft.net>,
        clang-built-linux@...glegroups.com,
        Nathan Chancellor <natechancellor@...il.com>,
        Ganesh Goudar <ganeshgr@...lsio.com>,
        Casey Leedom <leedom@...lsio.com>,
        Rahul Lakkireddy <rahul.lakkireddy@...lsio.com>,
        Arjun Vynipadath <arjun@...lsio.com>, netdev@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] chelsio: use BUG() instead of BUG_ON(1)

On Mon, Mar 25, 2019 at 5:49 AM Arnd Bergmann <arnd@...db.de> wrote:
>
> clang warns about possible bugs in a dead code branch after
> BUG_ON(1) when CONFIG_PROFILE_ALL_BRANCHES is enabled:
>
>  drivers/net/ethernet/chelsio/cxgb4/sge.c:479:3: error: variable 'buf_size' is used uninitialized whenever 'if'
>       condition is false [-Werror,-Wsometimes-uninitialized]
>                 BUG_ON(1);
>                 ^~~~~~~~~
>  include/asm-generic/bug.h:61:36: note: expanded from macro 'BUG_ON'
>  #define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0)
>                                    ^~~~~~~~~~~~~~~~~~~
>  include/linux/compiler.h:48:23: note: expanded from macro 'unlikely'
>  #  define unlikely(x)   (__branch_check__(x, 0, __builtin_constant_p(x)))
>                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  drivers/net/ethernet/chelsio/cxgb4/sge.c:482:9: note: uninitialized use occurs here
>         return buf_size;
>                ^~~~~~~~
>  drivers/net/ethernet/chelsio/cxgb4/sge.c:479:3: note: remove the 'if' if its condition is always true
>                 BUG_ON(1);
>                 ^
>  include/asm-generic/bug.h:61:32: note: expanded from macro 'BUG_ON'
>  #define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0)
>                                ^
>  drivers/net/ethernet/chelsio/cxgb4/sge.c:459:14: note: initialize the variable 'buf_size' to silence this warning
>         int buf_size;
>                     ^
>                      = 0
>
> Use BUG() here to create simpler code that clang understands
> correctly.

This is more concise and better expresses what we want to do here.
Thanks for the patch.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/net/ethernet/chelsio/cxgb4/cxgb4_debugfs.c | 2 +-
>  drivers/net/ethernet/chelsio/cxgb4/sge.c           | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_debugfs.c b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_debugfs.c
> index 3130b43bba52..02959035ed3f 100644
> --- a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_debugfs.c
> +++ b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_debugfs.c
> @@ -2620,7 +2620,7 @@ static inline struct port_info *ethqset2pinfo(struct adapter *adap, int qset)
>         }
>
>         /* should never happen! */
> -       BUG_ON(1);
> +       BUG();
>         return NULL;
>  }
>
> diff --git a/drivers/net/ethernet/chelsio/cxgb4/sge.c b/drivers/net/ethernet/chelsio/cxgb4/sge.c
> index 88773ca58e6b..b3da81e90132 100644
> --- a/drivers/net/ethernet/chelsio/cxgb4/sge.c
> +++ b/drivers/net/ethernet/chelsio/cxgb4/sge.c
> @@ -476,7 +476,7 @@ static inline int get_buf_size(struct adapter *adapter,
>                 break;
>
>         default:
> -               BUG_ON(1);
> +               BUG();
>         }
>
>         return buf_size;
> --
> 2.20.0
>


-- 
Thanks,
~Nick Desaulniers