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

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Message-Id: <20230912-bcachefs-warning-fixes-v1-7-a1cc83a38836@kernel.org>
Date:   Tue, 12 Sep 2023 12:15:44 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     kent.overstreet@...ux.dev
Cc:     bfoster@...hat.com, linux-bcachefs@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        patches@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH 7/7] bcachefs: Fix -Wcompare-distinct-pointer-types in
 bch2_copygc_get_buckets()

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>
---
 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