Patch "minmax: allow min()/max()/clamp() if the arguments have the same signedness." has been added to the 5.10-stable tree

gregkh
2025-10-17T13:48:46Z

This is a note to let you know that I've just added the patch titled

minmax: allow min()/max()/clamp() if the arguments have the same signedness.

to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
minmax-allow-min-max-clamp-if-the-arguments-have-the-same-signedness.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.

From prvs=378230090=farbere@amazon.com Fri Oct 17 11:08:35 2025
From: Eliav Farber <farbere@amazon.com>
Date: Fri, 17 Oct 2025 09:05:01 +0000
Subject: minmax: allow min()/max()/clamp() if the arguments have the same signedness.
To: <gregkh@linuxfoundation.org>, <stable@vger.kernel.org>, <linux@armlinux.org.uk>, <jdike@addtoit.com>, <richard@nod.at>, <anton.ivanov@cambridgegreys.com>, <dave.hansen@linux.intel.com>, <luto@kernel.org>, <peterz@infradead.org>, <tglx@linutronix.de>, <mingo@redhat.com>, <bp@alien8.de>, <x86@kernel.org>, <hpa@zytor.com>, <tony.luck@intel.com>, <qiuxu.zhuo@intel.com>, <mchehab@kernel.org>, <james.morse@arm.com>, <rric@kernel.org>, <harry.wentland@amd.com>, <sunpeng.li@amd.com>, <alexander.deucher@amd.com>, <christian.koenig@amd.com>, <airlied@linux.ie>, <daniel@ffwll.ch>, <evan.quan@amd.com>, <james.qian.wang@arm.com>, <liviu.dudau@arm.com>, <mihail.atanassov@arm.com>, <brian.starkey@arm.com>, <maarten.lankhorst@linux.intel.com>, <mripard@kernel.org>, <tzimmermann@suse.de>, <robdclark@gmail.com>, <sean@poorly.run>, <jdelvare@suse.com>, <linux@roeck-us.net>, <fery@cypress.com>, <dmitry.torokhov@gmail.com>, <agk@redhat.com>, <snitzer@redhat.com>, <dm-devel@redhat.com>, <rajur
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on.com>,
<sashal@kernel.org>, <ruanjinjie@huawei.com>, <David.Laight@ACULAB.COM>, <herve.codina@bootlin.com>, <Jason@zx2c4.com>, <keescook@chromium.org>, <kbusch@kernel.org>, <nathan@kernel.org>, <bvanassche@acm.org>, <ndesaulniers@google.com>, <linux-arm-kernel@lists.infradead.org>, <linux-kernel@vger.kernel.org>, <linux-um@lists.infradead.org>, <linux-edac@vger.kernel.org>, <amd-gfx@lists.freedesktop.org>, <dri-devel@lists.freedesktop.org>, <linux-arm-msm@vger.kernel.org>, <freedreno@lists.freedesktop.org>, <linux-hwmon@vger.kernel.org>, <linux-input@vger.kernel.org>, <linux-media@vger.kernel.org>, <netdev@vger.kernel.org>, <linux-stm32@st-md-mailman.stormreply.com>, <platform-driver-x86@vger.kernel.org>, <linux-scsi@vger.kernel.org>, <linux-staging@lists.linux.dev>, <linux-btrfs@vger.kernel.org>, <linux-erofs@lists.ozlabs.org>, <linux-ext4@vger.kernel.org>, <linux-sparse@vger.kernel.org>, <linux-mm@kvack.org>, <netfilter-devel@vger.kernel.org>, <coreteam@netfilter.org>, <tipc-dis
cussion@
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Cc: Christoph Hellwig <hch@infradead.org>, Linus Torvalds <torvalds@linux-foundation.org>
Message-ID: <20251017090519.46992-10-farbere@amazon.com>

From: David Laight <David.Laight@ACULAB.COM>

[ Upstream commit d03eba99f5bf7cbc6e2fdde3b6fa36954ad58e09 ]

The type-check in min()/max() is there to stop unexpected results if a
negative value gets converted to a large unsigned value. However it also
rejects 'unsigned int' v 'unsigned long' compares which are common and
never problematc.

Replace the 'same type' check with a 'same signedness' check.

The new test isn't itself a compile time error, so use static_assert() to
report the error and give a meaningful error message.

Due to the way builtin_choose_expr() works detecting the error in the
'non-constant' side (where static_assert() can be used) also detects
errors when the arguments are constant.

Link: https://lkml.kernel.org/r/fe7e6c542e094bfca655abcd323c1c98@AcuMS.aculab.com
Signed-off-by: David Laight <david.laight@aculab.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Eliav Farber <farbere@amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/minmax.h | 62 ++++++++++++++++++++++++++-----------------------
1 file changed, 33 insertions(+), 29 deletions(-)

--- a/include/linux/minmax.h
+++ b/include/linux/minmax.h
@@ -12,9 +12,8 @@
*
* - avoid multiple evaluations of the arguments (so side-effects like
* "x++" happen only once) when non-constant.
- * - perform strict type-checking (to generate warnings instead of
- * nasty runtime surprises). See the "unnecessary" pointer comparison
- * in __typecheck().
+ * - perform signed v unsigned type-checking (to generate compile
+ * errors instead of nasty runtime surprises).
* - retain result as a constant expressions when called with only
* constant expressions (to avoid tripping VLA warnings in stack
* allocation usage).
@@ -22,23 +21,30 @@
#define __typecheck(x, y) \
(!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))

-#define __no_side_effects(x, y) \
- (__is_constexpr(x) && __is_constexpr(y))
+/* is_signed_type() isn't a constexpr for pointer types */
+#define __is_signed(x) \
+ __builtin_choose_expr(__is_constexpr(is_signed_type(typeof(x))), \
+ is_signed_type(typeof(x)), 0)

-#define __safe_cmp(x, y) \
- (__typecheck(x, y) && __no_side_effects(x, y))
+#define __types_ok(x, y) \
+ (__is_signed(x) == __is_signed(y))

-#define __cmp(x, y, op) ((x) op (y) ? (x) : (y))
+#define __cmp_op_min <
+#define __cmp_op_max >

-#define __cmp_once(x, y, unique_x, unique_y, op) ({ \
+#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); \
- __cmp(unique_x, unique_y, op); })
-
-#define __careful_cmp(x, y, op) \
- __builtin_choose_expr(__safe_cmp(x, y), \
- __cmp(x, y, op), \
- __cmp_once(x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y), op))
+ 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); })
+
+#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)))

#define __clamp(val, lo, hi) \
((val) >= (hi) ? (hi) : ((val) <= (lo) ? (lo) : (val)))
@@ -47,17 +53,15 @@
typeof(val) unique_val = (val); \
typeof(lo) unique_lo = (lo); \
typeof(hi) unique_hi = (hi); \
+ static_assert(__builtin_choose_expr(__is_constexpr((lo) > (hi)), \
+ (lo) <= (hi), true), \
+ "clamp() low limit " #lo " greater than high limit " #hi); \
+ static_assert(__types_ok(val, lo), "clamp() 'lo' signedness error"); \
+ static_assert(__types_ok(val, hi), "clamp() 'hi' signedness error"); \
__clamp(unique_val, unique_lo, unique_hi); })

-#define __clamp_input_check(lo, hi) \
- (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
- __is_constexpr((lo) > (hi)), (lo) > (hi), false)))
-
#define __careful_clamp(val, lo, hi) ({ \
- __clamp_input_check(lo, hi) + \
- __builtin_choose_expr(__typecheck(val, lo) && __typecheck(val, hi) && \
- __typecheck(hi, lo) && __is_constexpr(val) && \
- __is_constexpr(lo) && __is_constexpr(hi), \
+ __builtin_choose_expr(__is_constexpr((val) - (lo) + (hi)), \
__clamp(val, lo, hi), \
__clamp_once(val, lo, hi, __UNIQUE_ID(__val), \
__UNIQUE_ID(__lo), __UNIQUE_ID(__hi))); })
@@ -67,14 +71,14 @@
* @x: first value
* @y: second value
*/
-#define min(x, y) __careful_cmp(x, y, <)
+#define min(x, y) __careful_cmp(min, x, y)

/**
* max - return maximum of two values of the same or compatible types
* @x: first value
* @y: second value
*/
-#define max(x, y) __careful_cmp(x, y, >)
+#define max(x, y) __careful_cmp(max, x, y)

/**
* umin - return minimum of two non-negative values
@@ -83,7 +87,7 @@
* @y: second value
*/
#define umin(x, y) \
- __careful_cmp((x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull, <)
+ __careful_cmp(min, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)

/**
* umax - return maximum of two non-negative values
@@ -91,7 +95,7 @@
* @y: second value
*/
#define umax(x, y) \
- __careful_cmp((x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull, >)
+ __careful_cmp(max, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)

/**
* min3 - return minimum of three values
@@ -143,7 +147,7 @@
* @x: first value
* @y: second value
*/
-#define min_t(type, x, y) __careful_cmp((type)(x), (type)(y), <)
+#define min_t(type, x, y) __careful_cmp(min, (type)(x), (type)(y))

/**
* max_t - return maximum of two values, using the specified type
@@ -151,7 +155,7 @@
* @x: first value
* @y: second value
*/
-#define max_t(type, x, y) __careful_cmp((type)(x), (type)(y), >)
+#define max_t(type, x, y) __careful_cmp(max, (type)(x), (type)(y))

/*
* Do not check the array parameter using __must_be_array().

Patches currently in stable-queue which might be from farbere@amazon.com are

queue-5.10/minmax-allow-comparisons-of-int-against-unsigned-char-short.patch
queue-5.10/minmax-add-a-few-more-min_t-max_t-users.patch
queue-5.10/minmax-improve-macro-expansion-and-type-checking.patch
queue-5.10/minmax-fix-indentation-of-__cmp_once-and-__clamp_once.patch
queue-5.10/minmax.h-simplify-the-variants-of-clamp.patch
queue-5.10/minmax-add-in_range-macro.patch
queue-5.10/minmax.h-move-all-the-clamp-definitions-after-the-min-max-ones.patch
queue-5.10/minmax-allow-min-max-clamp-if-the-arguments-have-the-same-signedness.patch
queue-5.10/minmax-don-t-use-max-in-situations-that-want-a-c-constant-expression.patch
queue-5.10/minmax.h-remove-some-defines-that-are-only-expanded-once.patch
queue-5.10/minmax.h-use-build_bug_on_msg-for-the-lo-hi-test-in-clamp.patch
queue-5.10/minmax-simplify-min-max-clamp-implementation.patch
queue-5.10/minmax-deduplicate-__unconst_integer_typeof.patch
queue-5.10/minmax-simplify-and-clarify-min_t-max_t-implementation.patch
queue-5.10/minmax.h-add-whitespace-around-operators-and-after-commas.patch
queue-5.10/minmax-sanity-check-constant-bounds-when-clamping.patch
queue-5.10/minmax-avoid-overly-complicated-constant-expressions-in-vm-code.patch
queue-5.10/minmax-make-generic-min-and-max-macros-available-everywhere.patch
queue-5.10/minmax-fix-up-min3-and-max3-too.patch
queue-5.10/minmax.h-reduce-the-define-expansion-of-min-max-and-clamp.patch
queue-5.10/minmax-fix-header-inclusions.patch
queue-5.10/minmax-introduce-min-max-_array.patch
queue-5.10/btrfs-remove-duplicated-in_range-macro.patch
queue-5.10/overflow-tracing-define-the-is_signed_type-macro-once.patch
queue-5.10/minmax-relax-check-to-allow-comparison-between-unsigned-arguments-and-signed-constants.patch
queue-5.10/minmax-clamp-more-efficiently-by-avoiding-extra-comparison.patch
queue-5.10/minmax.h-update-some-comments.patch