From: Jean Delvare Date: Thu, 20 Dec 2012 10:22:02 +0000 Subject: Re: [lm-sensors] [PATCH v2] linux/kernel.h: Fix DIV_ROUND_CLOSEST with unsigned divisors Message-Id: <20121220112202.3ead1fe1@endymion.delvare> List-Id: References: <1355928015-26212-1-git-send-email-linux@roeck-us.net> <20121219134721.bbde212f.akpm@linux-foundation.org> <20121219224122.GA26863@roeck-us.net> In-Reply-To: <20121219224122.GA26863@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Guenter Roeck Cc: Andrew Morton , linux-kernel@vger.kernel.org, lm-sensors@lm-sensors.org, Juergen Beisert Hi Guenter, On Wed, 19 Dec 2012 14:41:22 -0800, Guenter Roeck wrote: > On Wed, Dec 19, 2012 at 01:47:21PM -0800, Andrew Morton wrote: > > The changelog didn't describe the end-user visible effects of the bug. > > Please always include this information. Because... > > One observed effect is that the s2c_hwmon driver reports a value of 4198403 > instead of 0 if the ADC reads 0. > > Other impact is unpredictable. Problem is seen if the divisor is an unsigned > variable or constant and the dividend is less than (divisor/2). Really? In my own testing, the problem only shows with dividend = 0, and even then, only when dividend is signed and divisor is not. DIV_ROUND_CLOSEST(5, 20U) returns 0 as expected, and so do DIV_ROUND_CLOSEST(0 / 20), DIV_ROUND_CLOSEST(0U / 20) and DIV_ROUND_CLOSEST(0U / 20U). Are your observations different? > > The patch is applicable to 3.7.x. Should we backport it? > > Yes. DIV_ROUND_CLOSEST is used throughout the kernel, and impact is > unpredictable. > > 3.6 needs it as well. -- Jean Delvare _______________________________________________ lm-sensors mailing list lm-sensors@lm-sensors.org http://lists.lm-sensors.org/mailman/listinfo/lm-sensors