Patch "minmax.h: update some comments" has been added to the 5.15-stable tree

[<gregkh@linuxfoundation.org>]

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

    minmax.h: update some comments

to the 5.15-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.h-update-some-comments.patch
and it can be found in the queue-5.15 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=36971892a=farbere@amazon.com Wed Oct  8 17:34:21 2025
From: Eliav Farber <farbere@amazon.com>
Date: Wed, 8 Oct 2025 15:29:39 +0000
Subject: minmax.h: update some comments
To: <gregkh@linuxfoundation.org>, <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>, <james.morse@arm.com>, <rric@kernel.org>, <airlied@linux.ie>, <daniel@ffwll.ch>, <maarten.lankhorst@linux.intel.com>, <mripard@kernel.org>, <tzimmermann@suse.de>, <robdclark@gmail.com>, <sean@poorly.run>, <jdelvare@suse.com>, <linux@roeck-us.net>, <linus.walleij@linaro.org>, <dmitry.torokhov@gmail.com>, <maz@kernel.org>, <wens@csie.org>, <jernej.skrabec@gmail.com>, <agk@redhat.com>, <snitzer@redhat.com>, <dm-devel@redhat.com>, <davem@davemloft.net>, <kuba@kernel.org>, <mcoquelin.stm32@gmail.com>, <krzysztof.kozlowski@canonical.com>, <malattia@linux.it>, <hdegoede@redhat.com>, <mgross@linux.intel.com>, <jejb@linux.ibm.com>, <martin.petersen@oracle.com>, <sakari.ailus@l
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Cc: Arnd Bergmann <arnd@kernel.org>, Christoph Hellwig <hch@infradead.org>, Dan Carpenter <dan.carpenter@linaro.org>, "Jason A. Donenfeld" <Jason@zx2c4.com>, Jens Axboe <axboe@kernel.dk>, Lorenzo Stoakes <lorenzo.stoakes@oracle.com>, Mateusz Guzik <mjguzik@gmail.com>, "Pedro Falcato" <pedro.falcato@gmail.com>
Message-ID: <20251008152946.29285-15-farbere@amazon.com>

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

[ Upstream commit 10666e99204818ef45c702469488353b5bb09ec7 ]

- Change three to several.
- Remove the comment about retaining constant expressions, no longer true.
- Realign to nearer 80 columns and break on major punctiation.
- Add a leading comment to the block before __signed_type() and __is_nonneg()
  Otherwise the block explaining the cast is a bit 'floating'.
  Reword the rest of that comment to improve readability.

Link: https://lkml.kernel.org/r/85b050c81c1d4076aeb91a6cded45fee@AcuMS.aculab.com
Signed-off-by: David Laight <david.laight@aculab.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Arnd Bergmann <arnd@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dan Carpenter <dan.carpenter@linaro.org>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Pedro Falcato <pedro.falcato@gmail.com>
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 |   61 ++++++++++++++++++++++---------------------------
 1 file changed, 28 insertions(+), 33 deletions(-)

--- a/include/linux/minmax.h
+++ b/include/linux/minmax.h
@@ -8,13 +8,10 @@
 #include <linux/types.h>
 
 /*
- * min()/max()/clamp() macros must accomplish three things:
+ * min()/max()/clamp() macros must accomplish several things:
  *
  * - Avoid multiple evaluations of the arguments (so side-effects like
  *   "x++" happen only once) when non-constant.
- * - 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
@@ -31,25 +28,23 @@
  *   bit #0 set if ok for unsigned comparisons
  *   bit #1 set if ok for signed comparisons
  *
- * In particular, statically non-negative signed integer
- * expressions are ok for both.
+ * In particular, statically non-negative signed integer expressions
+ * are ok for both.
  *
- * NOTE! Unsigned types smaller than 'int' are implicitly
- * converted to 'int' in expressions, and are accepted for
- * signed conversions for now. This is debatable.
- *
- * Note that 'x' is the original expression, and 'ux' is
- * the unique variable that contains the value.
- *
- * We use 'ux' for pure type checking, and 'x' for when
- * we need to look at the value (but without evaluating
- * it for side effects! Careful to only ever evaluate it
- * with sizeof() or __builtin_constant_p() etc).
- *
- * Pointers end up being checked by the normal C type
- * rules at the actual comparison, and these expressions
- * only need to be careful to not cause warnings for
- * pointer use.
+ * NOTE! Unsigned types smaller than 'int' are implicitly converted to 'int'
+ * in expressions, and are accepted for signed conversions for now.
+ * This is debatable.
+ *
+ * Note that 'x' is the original expression, and 'ux' is the unique variable
+ * that contains the value.
+ *
+ * We use 'ux' for pure type checking, and 'x' for when we need to look at the
+ * value (but without evaluating it for side effects!
+ * Careful to only ever evaluate it with sizeof() or __builtin_constant_p() etc).
+ *
+ * Pointers end up being checked by the normal C type rules at the actual
+ * comparison, and these expressions only need to be careful to not cause
+ * warnings for pointer use.
  */
 #define __signed_type_use(x, ux) (2 + __is_nonneg(x, ux))
 #define __unsigned_type_use(x, ux) (1 + 2 * (sizeof(ux) < 4))
@@ -57,19 +52,19 @@
 	__signed_type_use(x, ux) : __unsigned_type_use(x, ux))
 
 /*
- * To avoid warnings about casting pointers to integers
- * of different sizes, we need that special sign type.
+ * Check whether a signed value is always non-negative.
  *
- * On 64-bit we can just always use 'long', since any
- * integer or pointer type can just be cast to that.
+ * A cast is needed to avoid any warnings from values that aren't signed
+ * integer types (in which case the result doesn't matter).
  *
- * This does not work for 128-bit signed integers since
- * the cast would truncate them, but we do not use s128
- * types in the kernel (we do use 'u128', but they will
- * be handled by the !is_signed_type() case).
- *
- * NOTE! The cast is there only to avoid any warnings
- * from when values that aren't signed integer types.
+ * On 64-bit any integer or pointer type can safely be cast to 'long'.
+ * But on 32-bit we need to avoid warnings about casting pointers to integers
+ * of different sizes without truncating 64-bit values so 'long' or 'long long'
+ * must be used depending on the size of the value.
+ *
+ * This does not work for 128-bit signed integers since the cast would truncate
+ * them, but we do not use s128 types in the kernel (we do use 'u128',
+ * but they are handled by the !is_signed_type() case).
  */
 #ifdef CONFIG_64BIT
   #define __signed_type(ux) long


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

queue-5.15/minmax-add-a-few-more-min_t-max_t-users.patch
queue-5.15/minmax-improve-macro-expansion-and-type-checking.patch
queue-5.15/minmax-fix-indentation-of-__cmp_once-and-__clamp_once.patch
queue-5.15/minmax.h-simplify-the-variants-of-clamp.patch
queue-5.15/minmax-add-in_range-macro.patch
queue-5.15/minmax.h-move-all-the-clamp-definitions-after-the-min-max-ones.patch
queue-5.15/minmax-don-t-use-max-in-situations-that-want-a-c-constant-expression.patch
queue-5.15/minmax.h-remove-some-defines-that-are-only-expanded-once.patch
queue-5.15/minmax.h-use-build_bug_on_msg-for-the-lo-hi-test-in-clamp.patch
queue-5.15/minmax-simplify-min-max-clamp-implementation.patch
queue-5.15/minmax-deduplicate-__unconst_integer_typeof.patch
queue-5.15/minmax-simplify-and-clarify-min_t-max_t-implementation.patch
queue-5.15/minmax.h-add-whitespace-around-operators-and-after-commas.patch
queue-5.15/minmax-avoid-overly-complicated-constant-expressions-in-vm-code.patch
queue-5.15/minmax-make-generic-min-and-max-macros-available-everywhere.patch
queue-5.15/minmax-fix-up-min3-and-max3-too.patch
queue-5.15/minmax.h-reduce-the-define-expansion-of-min-max-and-clamp.patch
queue-5.15/minmax-introduce-min-max-_array.patch
queue-5.15/minmax.h-update-some-comments.patch