From 6dc75ccba5680b67a4bcc72e96ec851326e66690 Mon Sep 17 00:00:00 2001 From: Stanislaw Gruszka Date: Thu, 7 Mar 2019 16:28:18 -0800 Subject: lib/div64.c: off by one in shift [ Upstream commit cdc94a37493135e355dfc0b0e086d84e3eadb50d ] 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@redhat.com Fixes: 658716d19f8f ("div64_u64(): improve precision on 32bit platforms") Signed-off-by: Stanislaw Gruszka Reported-by: Siarhei Volkau Tested-by: Siarhei Volkau Acked-by: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- lib/div64.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'lib') diff --git a/lib/div64.c b/lib/div64.c index 58e2a404097e..a2688b882461 100644 --- a/lib/div64.c +++ b/lib/div64.c @@ -103,7 +103,7 @@ u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder) 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) @@ -141,7 +141,7 @@ 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) -- cgit v1.2.3