From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753878AbbL0UGL (ORCPT ); Sun, 27 Dec 2015 15:06:11 -0500 Received: from spo001.leaseweb.nl ([83.149.101.17]:43662 "EHLO spo001.leaseweb.nl" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751872AbbL0UGH (ORCPT ); Sun, 27 Dec 2015 15:06:07 -0500 Date: Sun, 27 Dec 2015 21:06:04 +0100 From: Wim Van Sebroeck To: Jisheng Zhang Cc: linux-watchdog@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, sebastian.hesselbarth@gmail.com Subject: Re: [PATCH] watchdog: dw_wdt: fix signedness bug in dw_wdt_top_in_seconds() Message-ID: <20151227200604.GA24971@spo001.leaseweb.nl> References: <1450189527-1015-1-git-send-email-jszhang@marvell.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1450189527-1015-1-git-send-email-jszhang@marvell.com> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Jisheng, > On 64bit platforms, "(1 << (16 + top)) / clk_get_rate(dw_wdt.clk)" is > sign-extended to 64bit then converted to unsigned 64bit, finally divide > the clk rate. If the top is the maximum TOP i.e 15, "(1 << (16 +15))" > will be sign-extended to 0xffffffff80000000, then converted to unsigned > 0xffffffff80000000, which is a huge number, thus the final result is > wrong. > > We fix this issue by giving usigned value(1U in this case) at first. > > Let's assume clk rate is 25MHZ, > Before the patch: > dw_wdt_top_in_seconds(15) = -864612050 > > After the patch: > dw_wdt_top_in_seconds(15) = 85 > > Signed-off-by: Jisheng Zhang > --- > drivers/watchdog/dw_wdt.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/watchdog/dw_wdt.c b/drivers/watchdog/dw_wdt.c > index 6ea0634..8fefa4ad 100644 > --- a/drivers/watchdog/dw_wdt.c > +++ b/drivers/watchdog/dw_wdt.c > @@ -81,7 +81,7 @@ static inline int dw_wdt_top_in_seconds(unsigned top) > * There are 16 possible timeout values in 0..15 where the number of > * cycles is 2 ^ (16 + i) and the watchdog counts down. > */ > - return (1 << (16 + top)) / clk_get_rate(dw_wdt.clk); > + return (1U << (16 + top)) / clk_get_rate(dw_wdt.clk); > } > > static int dw_wdt_get_top(void) > -- > 2.6.4 > Patch is added to linux-watchdog-next. Kind regards, Wim.