Patch "minmax: fix up min3() and max3() too" has been added to the 6.1-stable tree

[gregkh at linuxfoundation.org]

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

    minmax: fix up min3() and max3() too

to the 6.1-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-fix-up-min3-and-max3-too.patch
and it can be found in the queue-6.1 subdirectory.

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


>From stable+bounces-183175-greg=kroah.com at vger.kernel.org Fri Oct  3 14:17:52 2025
From: Eliav Farber <farbere at amazon.com>
Date: Fri, 3 Oct 2025 12:15:13 +0000
Subject: minmax: fix up min3() and max3() too
To: <gregkh at linuxfoundation.org>, <kenneth.feng at amd.com>, <alexander.deucher at amd.com>, <christian.koenig at amd.com>, <airlied at gmail.com>, <simona at ffwll.ch>, <linus.walleij at linaro.org>, <dmitry.torokhov at gmail.com>, <tglx at linutronix.de>, <wens at csie.org>, <jernej.skrabec at gmail.com>, <samuel at sholland.org>, <agk at redhat.com>, <snitzer at kernel.org>, <mpatocka at redhat.com>, <clm at fb.com>, <dsterba at suse.com>, <luc.vanoostenryck at gmail.com>, <pmladek at suse.com>, <rostedt at goodmis.org>, <andriy.shevchenko at linux.intel.com>, <linux at rasmusvillemoes.dk>, <senozhatsky at chromium.org>, <akpm at linux-foundation.org>, <lijo.lazar at amd.com>, <asad.kamal at amd.com>, <kevinyang.wang at amd.com>, <David.Laight at ACULAB.COM>, <amd-gfx at lists.freedesktop.org>, <dri-devel at lists.freedesktop.org>, <linux-kernel at vger.kernel.org>, <linux-input at vger.kernel.org>, <linux-arm-kernel at lists.infradead.org>, <linux-sunxi at lists.linux.dev>, <dm-devel at lists.linux.dev>, <linux-btrfs at vger.kernel.org>, <linux-sparse at vger.kernel.org>, <stable at vger.
 kernel.org>, <farbere at amazon.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>, David Laight <David.Laight at aculab.com>, Arnd Bergmann <arnd at kernel.org>
Message-ID: <20251003121520.8176-5-farbere at amazon.com>

From: Linus Torvalds <torvalds at linux-foundation.org>

[ Upstream commit 21b136cc63d2a9ddd60d4699552b69c214b32964 ]

David Laight pointed out that we should deal with the min3() and max3()
mess too, which still does excessive expansion.

And our current macros are actually rather broken.

In particular, the macros did this:

  #define min3(x, y, z) min((typeof(x))min(x, y), z)
  #define max3(x, y, z) max((typeof(x))max(x, y), z)

and that not only is a nested expansion of possibly very complex
arguments with all that involves, the typing with that "typeof()" cast
is completely wrong.

For example, imagine what happens in max3() if 'x' happens to be a
'unsigned char', but 'y' and 'z' are 'unsigned long'.  The types are
compatible, and there's no warning - but the result is just random
garbage.

No, I don't think we've ever hit that issue in practice, but since we
now have sane infrastructure for doing this right, let's just use it.
It fixes any excessive expansion, and also avoids these kinds of broken
type issues.

Requested-by: David Laight <David.Laight at aculab.com>
Acked-by: Arnd Bergmann <arnd at kernel.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Eliav Farber <farbere at amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 include/linux/minmax.h |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--- a/include/linux/minmax.h
+++ b/include/linux/minmax.h
@@ -152,13 +152,20 @@
 #define umax(x, y)	\
 	__careful_cmp(max, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)
 
+#define __careful_op3(op, x, y, z, ux, uy, uz) ({			\
+	__auto_type ux = (x); __auto_type uy = (y);__auto_type uz = (z);\
+	BUILD_BUG_ON_MSG(!__types_ok3(x,y,z,ux,uy,uz),			\
+		#op"3("#x", "#y", "#z") signedness error");		\
+	__cmp(op, ux, __cmp(op, uy, uz)); })
+
 /**
  * min3 - return minimum of three values
  * @x: first value
  * @y: second value
  * @z: third value
  */
-#define min3(x, y, z) min((typeof(x))min(x, y), z)
+#define min3(x, y, z) \
+	__careful_op3(min, x, y, z, __UNIQUE_ID(x_), __UNIQUE_ID(y_), __UNIQUE_ID(z_))
 
 /**
  * max3 - return maximum of three values
@@ -166,7 +173,8 @@
  * @y: second value
  * @z: third value
  */
-#define max3(x, y, z) max((typeof(x))max(x, y), z)
+#define max3(x, y, z) \
+	__careful_op3(max, x, y, z, __UNIQUE_ID(x_), __UNIQUE_ID(y_), __UNIQUE_ID(z_))
 
 /**
  * min_not_zero - return the minimum that is _not_ zero, unless both are zero


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

queue-6.1/minmax-improve-macro-expansion-and-type-checking.patch
queue-6.1/minmax.h-simplify-the-variants-of-clamp.patch
queue-6.1/minmax.h-move-all-the-clamp-definitions-after-the-min-max-ones.patch
queue-6.1/minmax-don-t-use-max-in-situations-that-want-a-c-constant-expression.patch
queue-6.1/minmax.h-remove-some-defines-that-are-only-expanded-once.patch
queue-6.1/minmax.h-use-build_bug_on_msg-for-the-lo-hi-test-in-clamp.patch
queue-6.1/minmax-simplify-min-max-clamp-implementation.patch
queue-6.1/minmax.h-add-whitespace-around-operators-and-after-commas.patch
queue-6.1/minmax-fix-up-min3-and-max3-too.patch
queue-6.1/minmax.h-reduce-the-define-expansion-of-min-max-and-clamp.patch
queue-6.1/minmax.h-update-some-comments.patch