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=-9.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,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 7EFCDC282CE for ; Wed, 24 Apr 2019 17:15:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4936921900 for ; Wed, 24 Apr 2019 17:15:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556126145; bh=mDsO01OQwLrVPDFden1Z1tgb2VD5F43m3zxQ4gMJttQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=DZFK2sRexsORPykNOi5zlLQVaGGSXwW0g83Lg9ZPjW5ZBE07cVMDcZt8XqxdcRlfY Vfw4aKDtc3bxdMdms9oyB1500jHJ8UgKT+pNG/ltSBYTqrUdhXlZuXyfUPdTguedju 2C3sen+hVGiw4TSGc0lG4KaJERpTHRqSE6m0BJDc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387478AbfDXRPo (ORCPT ); Wed, 24 Apr 2019 13:15:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:40116 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387657AbfDXRPi (ORCPT ); Wed, 24 Apr 2019 13:15:38 -0400 Received: from localhost (62-193-50-229.as16211.net [62.193.50.229]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AC9082054F; Wed, 24 Apr 2019 17:15:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556126138; bh=mDsO01OQwLrVPDFden1Z1tgb2VD5F43m3zxQ4gMJttQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=2SbOA2o0L/XI6AuD7AB6zfZv3HueoRKtT6o7ovZVShd3pTy6YQ10alSSb+CQOt51/ fyyx34NfBc2odyKui9x2wS65qcy5LJlgB+1i9rLCl1YzFGlhuxlFFjGbKklFvnqz5l RYWSUy/IQjmPA0PcXIIws0Myc5Xztq/39Tq9o1e0= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Stanislaw Gruszka , Siarhei Volkau , Oleg Nesterov , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH 3.18 084/104] lib/div64.c: off by one in shift Date: Wed, 24 Apr 2019 19:09:41 +0200 Message-Id: <20190424170908.041845700@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190424170839.996641496@linuxfoundation.org> References: <20190424170839.996641496@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [ 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