The patch titled
Subject: include/linux/math.h: fix mult_frac() multiple argument evaluation bug
has been added to the -mm mm-nonmm-unstable branch. Its filename is
fix-mult_frac-multiple-argument-evaluation-bug.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fix-mult_frac-multiple-argument-evaluation-bug.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: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Subject: include/linux/math.h: fix mult_frac() multiple argument evaluation bug
Date: Sat, 20 May 2023 21:25:19 +0300
mult_frac() evaluates _all_ arguments multiple times in the body.
Clarify comment while I'm at it.
Link: https://lkml.kernel.org/r/f9f9fdbb-ec8e-4f5e-a998-2a58627a1a43@p183
Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/math.h | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)
--- a/include/linux/math.h~fix-mult_frac-multiple-argument-evaluation-bug
+++ a/include/linux/math.h
@@ -118,17 +118,17 @@ __STRUCT_FRACT(s32)
__STRUCT_FRACT(u32)
#undef __STRUCT_FRACT
-/*
- * Multiplies an integer by a fraction, while avoiding unnecessary
- * overflow or loss of precision.
- */
-#define mult_frac(x, numer, denom)( \
-{ \
- typeof(x) quot = (x) / (denom); \
- typeof(x) rem = (x) % (denom); \
- (quot * (numer)) + ((rem * (numer)) / (denom)); \
-} \
-)
+/* Calculate "x * n / d" without unnecessary overflow or loss of precision. */
+#define mult_frac(x, n, d) \
+({ \
+ typeof(x) x_ = (x); \
+ typeof(n) n_ = (n); \
+ typeof(d) d_ = (d); \
+ \
+ typeof(x_) q = x_ / d_; \
+ typeof(x_) r = x_ % d_; \
+ q * n_ + r * n_ / d_; \
+})
#define sector_div(a, b) do_div(a, b)
_
Patches currently in -mm which might be from adobriyan@xxxxxxxxx are
add-intptr_t.patch
fix-mult_frac-multiple-argument-evaluation-bug.patch
