linux-kernel - Re: [PATCH] dm dust: Convert an 'else if' into an 'else' in dust

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Message-ID: <CAKwvOdkNMnwRC9UO_cJq+e9+x5DHE0Nw0guzThxU_RX5obfSPQ@mail.gmail.com>
Date:   Tue, 30 Apr 2019 15:31:27 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] dm dust: Convert an 'else if' into an 'else' in dust_map

On Mon, Apr 29, 2019 at 7:10 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> When building with -Wsometimes-uninitialized, Clang warns:
>
> drivers/md/dm-dust.c:216:11: warning: variable 'ret' is used
> uninitialized whenever 'if' condition is false
> [-Wsometimes-uninitialized]
>         else if (bio_data_dir(bio) == WRITE)
>                  ^~~~~~~~~~~~~~~~~~~~~~~~~~
> include/linux/bio.h:69:2: note: expanded from macro 'bio_data_dir'
>         (op_is_write(bio_op(bio)) ? WRITE : READ)
>         ^
> drivers/md/dm-dust.c:219:9: note: uninitialized use occurs here
>         return ret;
>                ^~~
> drivers/md/dm-dust.c:216:7: note: remove the 'if' if its condition is
> always true
>         else if (bio_data_dir(bio) == WRITE)
>              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/md/dm-dust.c:209:9: note: initialize the variable 'ret' to
> silence this warning
>         int ret;
>                ^
>                 = 0
> 1 warning generated.
>
> It isn't wrong; however, bio_data_dir will only ever return READ and
> WRITE so the second 'else if' can really become an 'else' to silence
> this warning and not change the final meaning of the code.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/462
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  drivers/md/dm-dust.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/md/dm-dust.c b/drivers/md/dm-dust.c
> index 997830984893..5baeb56679ed 100644
> --- a/drivers/md/dm-dust.c
> +++ b/drivers/md/dm-dust.c
> @@ -213,7 +213,7 @@ static int dust_map(struct dm_target *ti, struct bio *bio)
>
>         if (bio_data_dir(bio) == READ)
>                 ret = dust_map_read(dd, bio->bi_iter.bi_sector, dd->fail_read_on_bb);
> -       else if (bio_data_dir(bio) == WRITE)
> +       else
>                 ret = dust_map_write(dd, bio->bi_iter.bi_sector, dd->fail_read_on_bb);
>
>         return ret;
> --
> 2.21.0
>

Thanks for the patch.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
-- 
Thanks,
~Nick Desaulniers