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 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-fix-up-min3-and-max3-too.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 <[email protected]> know about it.
>From [email protected] Fri Oct 17 11:12:01 2025
From: Eliav Farber <[email protected]>
Date: Fri, 17 Oct 2025 09:05:12 +0000
Subject: minmax: fix up min3() and max3() too
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Cc: Linus Torvalds <[email protected]>, David Laight
<[email protected]>, Arnd Bergmann <[email protected]>
Message-ID: <[email protected]>
From: Linus Torvalds <[email protected]>
[ 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 <[email protected]>
Acked-by: Arnd Bergmann <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Eliav Farber <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
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 [email protected] 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
