[PATCH] overflow: Match arithmetic in both parts of __builtin_choose_expr

[Bill Wendling <morbo@google.com>]

The two parts of the '__builtin_choose_expr()' had different arithmetic
expressions. This patch correct it so that both parts calculate:

  COUNT * sizeof(*MEMBER) + __must_be_array(MEMBER)

In practice, the call to '__must_be_array' is meant to assert if
'MEMBER' isn't an array and return '0' otherwise. However, symmetry is
less prone to subtle errors (and far more satisfying).

Fixes: 230f6fa2c1db ("overflow: Provide constant expression struct_size")
Signed-off-by: Bill Wendling <morbo@google.com>
---
 include/linux/overflow.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index a8cb6319b4fb..265ec265aa3e 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -418,7 +418,8 @@ static __always_inline size_t __must_check size_sub(size_t minuend, size_t subtr
 #define flex_array_size(p, member, count)				\
 	__builtin_choose_expr(__is_constexpr(count),			\
 		(count) * sizeof(*(p)->member) + __must_be_array((p)->member),	\
-		size_mul(count, sizeof(*(p)->member) + __must_be_array((p)->member)))
+		size_add(size_mul(count, sizeof(*(p)->member)),		\
+			 __must_be_array((p)->member)))
 
 /**
  * struct_size() - Calculate size of structure with trailing flexible array.
-- 
2.56.0.385.gd3acb90ef8-goog