+ lib-mul_u64_u64_div_u64-combine-overflow-and-divide-by-zero-checks.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

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The patch titled
     Subject: lib: mul_u64_u64_div_u64(): combine overflow and divide by zero checks
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     lib-mul_u64_u64_div_u64-combine-overflow-and-divide-by-zero-checks.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/lib-mul_u64_u64_div_u64-combine-overflow-and-divide-by-zero-checks.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: David Laight <david.laight.linux@gmail.com>
Subject: lib: mul_u64_u64_div_u64(): combine overflow and divide by zero checks
Date: Wed, 5 Nov 2025 20:10:28 +0000

Since the overflow check always triggers when the divisor is zero
move the check for divide by zero inside the overflow check.
This means there is only one test in the normal path.

Link: https://lkml.kernel.org/r/20251105201035.64043-3-david.laight.linux@gmail.com
Signed-off-by: David Laight <david.laight.linux@gmail.com>
Reviewed-by: Nicolas Pitre <npitre@baylibre.com>
Cc: Biju Das <biju.das.jz@bp.renesas.com>
Cc: Borislav Betkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Li RongQing <lirongqing@baidu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/math/div64.c |   21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

--- a/lib/math/div64.c~lib-mul_u64_u64_div_u64-combine-overflow-and-divide-by-zero-checks
+++ a/lib/math/div64.c
@@ -212,12 +212,16 @@ u64 mul_u64_u64_div_u64(u64 a, u64 b, u6
 
 #endif
 
-	/* make sure d is not zero, trigger runtime exception otherwise */
-	if (unlikely(d == 0)) {
-		unsigned long zero = 0;
-
-		OPTIMIZER_HIDE_VAR(zero);
-		return ~0UL/zero;
+	if (unlikely(n_hi >= d)) {
+		/* trigger runtime exception if divisor is zero */
+		if (d == 0) {
+			unsigned long zero = 0;
+
+			OPTIMIZER_HIDE_VAR(zero);
+			return ~0UL/zero;
+		}
+		/* overflow: result is unrepresentable in a u64 */
+		return ~0ULL;
 	}
 
 	int shift = __builtin_ctzll(d);
@@ -234,11 +238,6 @@ u64 mul_u64_u64_div_u64(u64 a, u64 b, u6
 		 */
 	}
 
-	if (n_hi >= d) {
-		/* overflow: result is unrepresentable in a u64 */
-		return -1;
-	}
-
 	/* Do the full 128 by 64 bits division */
 
 	shift = __builtin_clzll(d);
_

Patches currently in -mm which might be from david.laight.linux@gmail.com are

lib-mul_u64_u64_div_u64-rename-parameter-c-to-d.patch
lib-mul_u64_u64_div_u64-combine-overflow-and-divide-by-zero-checks.patch
lib-mul_u64_u64_div_u64-simplify-check-for-a-64bit-product.patch
lib-add-mul_u64_add_u64_div_u64-and-mul_u64_u64_div_u64_roundup.patch
lib-add-tests-for-mul_u64_u64_div_u64_roundup.patch
lib-test_mul_u64_u64_div_u64-test-both-generic-and-arch-versions.patch
lib-mul_u64_u64_div_u64-optimise-multiply-on-32bit-x86.patch
lib-mul_u64_u64_div_u64-optimise-the-divide-code.patch
lib-test_mul_u64_u64_div_u64-test-the-32bit-code-on-64bit.patch