linux-kernel - Re: [PATCH] dm flakey: Fix clang -Wparentheses-equality in flakey

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Date:   Thu, 2 Feb 2023 11:00:37 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     agk@...hat.com, snitzer@...nel.org, trix@...hat.com,
        sweettea-kernel@...miny.me, mpatocka@...hat.com,
        dm-devel@...hat.com, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, patches@...ts.linux.dev
Subject: Re: [PATCH] dm flakey: Fix clang -Wparentheses-equality in flakey_map()

On Thu, Feb 2, 2023 at 9:00 AM Nathan Chancellor <nathan@...nel.org> wrote:
>
> Clang warns:
>
>   ../drivers/md/dm-flakey.c:369:28: error: equality comparison with extraneous parentheses [-Werror,-Wparentheses-equality]
>                           if ((fc->corrupt_bio_rw == WRITE)) {
>                                ~~~~~~~~~~~~~~~~~~~^~~~~~~~
>   ../drivers/md/dm-flakey.c:369:28: note: remove extraneous parentheses around the comparison to silence this warning
>                           if ((fc->corrupt_bio_rw == WRITE)) {
>                               ~                   ^       ~
>   ../drivers/md/dm-flakey.c:369:28: note: use '=' to turn this equality comparison into an assignment
>                           if ((fc->corrupt_bio_rw == WRITE)) {
>                                                   ^~
>                                                   =
>   1 error generated.
>
> GCC only warns when one set of parentheses are used for assignment
> expressions, whereas clang additionally warns when two sets of
> parentheses are used for equality comparisons. Remove the extra set of
> parentheses to silence the warning as it suggests, as this is obviously
> supposed to be an equality comparison.
>
> Fixes: 0e766389cedc ("dm flakey: fix logic when corrupting a bio")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1798
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

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

> ---
> I do not mind this change being squashed with the offending commit, as I
> noticed it was Cc'd for stable, which would minimize the chance for
> breakage.
> ---
>  drivers/md/dm-flakey.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/md/dm-flakey.c b/drivers/md/dm-flakey.c
> index 08f9aa476d97..335684a1aeaa 100644
> --- a/drivers/md/dm-flakey.c
> +++ b/drivers/md/dm-flakey.c
> @@ -366,7 +366,7 @@ static int flakey_map(struct dm_target *ti, struct bio *bio)
>                  * Corrupt matching writes.
>                  */
>                 if (fc->corrupt_bio_byte) {
> -                       if ((fc->corrupt_bio_rw == WRITE)) {
> +                       if (fc->corrupt_bio_rw == WRITE) {
>                                 if (all_corrupt_bio_flags_match(bio, fc))
>                                         corrupt_bio_data(bio, fc);
>                         }
>
> ---
> base-commit: 6f30cc248507ee96c22ff4c3cbc86099ff12b7a9
> change-id: 20230202-dm-parenthesis-warning-6139f4b5020b
>
> Best regards,
> --
> Nathan Chancellor <nathan@...nel.org>
>


-- 
Thanks,
~Nick Desaulniers