Patch "minmax: relax check to allow comparison between unsigned arguments and signed constants" has been added to the 5.10-stable tree

[<gregkh@linuxfoundation.org>]

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

    minmax: relax check to allow comparison between unsigned arguments and signed constants

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-relax-check-to-allow-comparison-between-unsigned-arguments-and-signed-constants.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 11:09:53 2025
From: Eliav Farber <farbere@amazon.com>
Date: Fri, 17 Oct 2025 09:05:04 +0000
Subject: minmax: relax check to allow comparison between unsigned arguments and signed constants
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
 @chelsio
 .com>, <davem@davemloft.net>, <kuba@kernel.org>, <peppe.cavallaro@st.com>, <alexandre.torgue@st.com>, <joabreu@synopsys.com>, <mcoquelin.stm32@gmail.com>, <malattia@linux.it>, <hdegoede@redhat.com>, <mgross@linux.intel.com>, <intel-linux-scu@intel.com>, <artur.paszkiewicz@intel.com>, <jejb@linux.ibm.com>, <martin.petersen@oracle.com>, <sakari.ailus@linux.intel.com>, <clm@fb.com>, <josef@toxicpanda.com>, <dsterba@suse.com>, <xiang@kernel.org>, <chao@kernel.org>, <jack@suse.com>, <tytso@mit.edu>, <adilger.kernel@dilger.ca>, <dushistov@mail.ru>, <luc.vanoostenryck@gmail.com>, <rostedt@goodmis.org>, <pmladek@suse.com>, <sergey.senozhatsky@gmail.com>, <andriy.shevchenko@linux.intel.com>, <linux@rasmusvillemoes.dk>, <minchan@kernel.org>, <ngupta@vflare.org>, <akpm@linux-foundation.org>, <kuznet@ms2.inr.ac.ru>, <yoshfuji@linux-ipv6.org>, <pablo@netfilter.org>, <kadlec@netfilter.org>, <fw@strlen.de>, <jmaloy@redhat.com>, <ying.xue@windriver.com>, <willy@infradead.org>, <farbere@amaz
 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@
 lists.sourceforge.net>
Cc: Christoph Hellwig <hch@infradead.org>, Linus Torvalds <torvalds@linux-foundation.org>
Message-ID: <20251017090519.46992-13-farbere@amazon.com>

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

[ Upstream commit 867046cc7027703f60a46339ffde91a1970f2901 ]

Allow (for example) min(unsigned_var, 20).

The opposite min(signed_var, 20u) is still errored.

Since a comparison between signed and unsigned never makes the unsigned
value negative it is only necessary to adjust the __types_ok() test.

Link: https://lkml.kernel.org/r/633b64e2f39e46bb8234809c5595b8c7@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 |   24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

--- a/include/linux/minmax.h
+++ b/include/linux/minmax.h
@@ -10,13 +10,18 @@
 /*
  * min()/max()/clamp() macros must accomplish three things:
  *
- * - avoid multiple evaluations of the arguments (so side-effects like
+ * - Avoid multiple evaluations of the arguments (so side-effects like
  *   "x++" happen only once) when non-constant.
- * - 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
+ * - Retain result as a constant expressions when called with only
  *   constant expressions (to avoid tripping VLA warnings in stack
  *   allocation usage).
+ * - Perform signed v unsigned type-checking (to generate compile
+ *   errors instead of nasty runtime surprises).
+ * - Unsigned char/short are always promoted to signed int and can be
+ *   compared against signed or unsigned arguments.
+ * - Unsigned arguments can be compared against non-negative signed constants.
+ * - Comparison of a signed argument against an unsigned constant fails
+ *   even if the constant is below __INT_MAX__ and could be cast to int.
  */
 #define __typecheck(x, y) \
 	(!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
@@ -26,9 +31,14 @@
 	__builtin_choose_expr(__is_constexpr(is_signed_type(typeof(x))),	\
 		is_signed_type(typeof(x)), 0)
 
-#define __types_ok(x, y) 			\
-	(__is_signed(x) == __is_signed(y) ||	\
-		__is_signed((x) + 0) == __is_signed((y) + 0))
+/* True for a non-negative signed int constant */
+#define __is_noneg_int(x)	\
+	(__builtin_choose_expr(__is_constexpr(x) && __is_signed(x), x, -1) >= 0)
+
+#define __types_ok(x, y) 					\
+	(__is_signed(x) == __is_signed(y) ||			\
+		__is_signed((x) + 0) == __is_signed((y) + 0) ||	\
+		__is_noneg_int(x) || __is_noneg_int(y))
 
 #define __cmp_op_min <
 #define __cmp_op_max >


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