linux-kernel - [PATCH 08/19 5.15.y] minmax: simplify and clarify min_t()/max

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Message-ID: <20251002204733.35652-9-farbere@amazon.com>
Date: Thu, 2 Oct 2025 20:47:22 +0000
From: Eliav Farber <farbere@...zon.com>
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CC: Linus Torvalds <torvalds@...ux-foundation.org>, David Laight
	<David.Laight@...lab.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Subject: [PATCH 08/19 5.15.y] minmax: simplify and clarify min_t()/max_t() implementation

From: Linus Torvalds <torvalds@...ux-foundation.org>

commit 017fa3e89187848fd056af757769c9e66ac3e93d upstream.

This simplifies the min_t() and max_t() macros by no longer making them
work in the context of a C constant expression.

That means that you can no longer use them for static initializers or
for array sizes in type definitions, but there were only a couple of
such uses, and all of them were converted (famous last words) to use
MIN_T/MAX_T instead.

Cc: David Laight <David.Laight@...lab.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Eliav Farber <farbere@...zon.com>
---
 include/linux/minmax.h | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/include/linux/minmax.h b/include/linux/minmax.h
index 2a40d3550f28..fc384714da45 100644
--- a/include/linux/minmax.h
+++ b/include/linux/minmax.h
@@ -45,17 +45,20 @@
 
 #define __cmp(op, x, y)	((x) __cmp_op_##op (y) ? (x) : (y))
 
-#define __cmp_once(op, x, y, unique_x, unique_y) ({	\
-	typeof(x) unique_x = (x);			\
-	typeof(y) unique_y = (y);			\
+#define __cmp_once_unique(op, type, x, y, ux, uy) \
+	({ type ux = (x); type uy = (y); __cmp(op, ux, uy); })
+
+#define __cmp_once(op, type, x, y) \
+	__cmp_once_unique(op, type, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
+
+#define __careful_cmp_once(op, x, y) ({			\
 	static_assert(__types_ok(x, y),			\
 		#op "(" #x ", " #y ") signedness error, fix types or consider u" #op "() before " #op "_t()"); \
-	__cmp(op, unique_x, unique_y); })
+	__cmp_once(op, __auto_type, x, y); })
 
 #define __careful_cmp(op, x, y)					\
 	__builtin_choose_expr(__is_constexpr((x) - (y)),	\
-		__cmp(op, x, y),				\
-		__cmp_once(op, x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y)))
+		__cmp(op, x, y), __careful_cmp_once(op, x, y))
 
 #define __clamp(val, lo, hi)	\
 	((val) >= (hi) ? (hi) : ((val) <= (lo) ? (lo) : (val)))
@@ -158,7 +161,7 @@
  * @x: first value
  * @y: second value
  */
-#define min_t(type, x, y)	__careful_cmp(min, (type)(x), (type)(y))
+#define min_t(type, x, y) __cmp_once(min, type, x, y)
 
 /**
  * max_t - return maximum of two values, using the specified type
@@ -166,7 +169,7 @@
  * @x: first value
  * @y: second value
  */
-#define max_t(type, x, y)	__careful_cmp(max, (type)(x), (type)(y))
+#define max_t(type, x, y) __cmp_once(max, type, x, y)
 
 /*
  * Do not check the array parameter using __must_be_array().
-- 
2.47.3