From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3A88FC43381 for ; Sat, 30 Mar 2019 01:32:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 00703217F5 for ; Sat, 30 Mar 2019 01:32:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553909579; bh=kOvRqM021NlXDBzpWaW6VhZwLf+FhgwRIZlIkjLWnsQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=zcuB1vAE0dtCw1mUiCnYsKbqAfb1MFQe6l4TUDfn0Jx7X2ZmD01Du/2IMouP2KGWg EYFlI1c19wrybRedPsq4QLERl8nwCq0WXeyg5LgzQ01ousmNL/niuRFf5jUoD/mt4Z JpB3rw7czmncw5wsOHX7rfeq5vTCR+/1oBn94cI0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732436AbfC3Bc5 (ORCPT ); Fri, 29 Mar 2019 21:32:57 -0400 Received: from mail.kernel.org ([198.145.29.99]:40834 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732416AbfC3Bcp (ORCPT ); Fri, 29 Mar 2019 21:32:45 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 861832184C; Sat, 30 Mar 2019 01:32:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553909564; bh=kOvRqM021NlXDBzpWaW6VhZwLf+FhgwRIZlIkjLWnsQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=I1QyIcyYXyeefL2P0zze+T8zarvUVs1Xp4xVWLQzxiRwqZ/A31RyprjuSwY0hqe1g LbomrjSkWpjSpIU80UbDkgqOSCklWcvFe0zLeNjDkcDxvq0jdsWNrygSQdD2qtzZgP +5h1WCsGufiTpFyJ1Gkxh3kLv/5OGI7HiCN70Ioo= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Stanislaw Gruszka , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH AUTOSEL 3.18 09/10] lib/div64.c: off by one in shift Date: Fri, 29 Mar 2019 21:32:26 -0400 Message-Id: <20190330013227.1365-9-sashal@kernel.org> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20190330013227.1365-1-sashal@kernel.org> References: <20190330013227.1365-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Stanislaw Gruszka [ 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(-) diff --git a/lib/div64.c b/lib/div64.c index 4382ad77777e..ce76dc3d674e 100644 --- a/lib/div64.c +++ b/lib/div64.c @@ -100,7 +100,7 @@ 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) @@ -138,7 +138,7 @@ 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) -- 2.19.1