The patch titled
Subject: lib/div64.c: off by one in shift
has been added to the -mm tree. Its filename is
lib-div64-off-by-one-in-shift.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/lib-div64-off-by-one-in-shift.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/lib-div64-off-by-one-in-shift.patch
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------------------------------------------------------
From: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
Subject: lib/div64.c: off by one in shift
fls counts bits starting from 1 to 32 (returns 0 for zero argument). If
we add 1 we shift right one bit more and loose precision from divisor,
what cause function incorect results with some numbers.
Corrected code was tested in user-space, see bugzilla:
https://bugzilla.kernel.org/show_bug.cgi?id=202391
Link: http://lkml.kernel.org/r/1548686944-11891-1-git-send-email-sgruszka@xxxxxxxxxx
Fixes: 658716d19f8f ("div64_u64(): improve precision on 32bit platforms")
Signed-off-by: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
Reported-by: Siarhei Volkau <lis8215@xxxxxxxxx>
Tested-by: Siarhei Volkau <lis8215@xxxxxxxxx>
Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/div64.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/lib/div64.c~lib-div64-off-by-one-in-shift
+++ a/lib/div64.c
@@ -109,7 +109,7 @@ u64 div64_u64_rem(u64 dividend, u64 divi
quot = div_u64_rem(dividend, divisor, &rem32);
*remainder = rem32;
} else {
- int n = 1 + fls(high);
+ int n = fls(high);
quot = div_u64(dividend >> n, divisor >> n);
if (quot != 0)
@@ -147,7 +147,7 @@ u64 div64_u64(u64 dividend, u64 divisor)
if (high == 0) {
quot = div_u64(dividend, divisor);
} else {
- int n = 1 + fls(high);
+ int n = fls(high);
quot = div_u64(dividend >> n, divisor >> n);
if (quot != 0)
_
Patches currently in -mm which might be from sgruszka@xxxxxxxxxx are
lib-div64-off-by-one-in-shift.patch
