linux-kernel - Re: [PATCH 7/7] bcachefs: Fix -Wcompare-distinct-pointer-types in bch2_copygc_get

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Message-ID: <20230913220627.stso6sxqyraizqod@google.com>
Date:   Wed, 13 Sep 2023 22:06:27 +0000
From:   Justin Stitt <justinstitt@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     kent.overstreet@...ux.dev, bfoster@...hat.com,
        linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, patches@...ts.linux.dev
Subject: Re: [PATCH 7/7] bcachefs: Fix -Wcompare-distinct-pointer-types in
 bch2_copygc_get_buckets()

On Tue, Sep 12, 2023 at 12:15:44PM -0700, Nathan Chancellor wrote:
> When building bcachefs for 32-bit ARM, there is a warning when using
> max() to compare an expression involving 'size_t' with an 'unsigned
> long' literal:
>
>   fs/bcachefs/movinggc.c:159:21: error: comparison of distinct pointer types ('typeof (16UL) *' (aka 'unsigned long *') and 'typeof (buckets_in_flight->nr / 4) *' (aka 'unsigned int *')) [-Werror,-Wcompare-distinct-pointer-types]
>     159 |         size_t nr_to_get = max(16UL, buckets_in_flight->nr / 4);
>         |                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   include/linux/minmax.h:76:19: note: expanded from macro 'max'
>      76 | #define max(x, y)       __careful_cmp(x, y, >)
>         |                         ^~~~~~~~~~~~~~~~~~~~~~
>   include/linux/minmax.h:38:24: note: expanded from macro '__careful_cmp'
>      38 |         __builtin_choose_expr(__safe_cmp(x, y), \
>         |                               ^~~~~~~~~~~~~~~~
>   include/linux/minmax.h:28:4: note: expanded from macro '__safe_cmp'
>      28 |                 (__typecheck(x, y) && __no_side_effects(x, y))
>         |                  ^~~~~~~~~~~~~~~~~
>   include/linux/minmax.h:22:28: note: expanded from macro '__typecheck'
>      22 |         (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
>         |                    ~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~
>   1 error generated.
>
> On 64-bit architectures, size_t is 'unsigned long', so there is no
> warning when comparing these two expressions. Use max_t(size_t, ...) for
> this situation, eliminating the warning.
>
> Fixes: dd49018737d4 ("bcachefs: Rhashtable based buckets_in_flight for copygc")
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
Reviewed-by: Justin Stitt <justinstitt@...gle.com>
> ---
>  fs/bcachefs/movinggc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/bcachefs/movinggc.c b/fs/bcachefs/movinggc.c
> index 256431a6dc0c..1cb441d90b34 100644
> --- a/fs/bcachefs/movinggc.c
> +++ b/fs/bcachefs/movinggc.c
> @@ -156,7 +156,7 @@ static int bch2_copygc_get_buckets(struct btree_trans *trans,
>  	struct bch_fs *c = trans->c;
>  	struct btree_iter iter;
>  	struct bkey_s_c k;
> -	size_t nr_to_get = max(16UL, buckets_in_flight->nr / 4);
> +	size_t nr_to_get = max_t(size_t, 16U, buckets_in_flight->nr / 4);
>  	size_t saw = 0, in_flight = 0, not_movable = 0, sectors = 0;
>  	int ret;
>
>
> --
> 2.42.0
>