From: Andrew Morton Date: Wed, 19 Dec 2012 21:47:21 +0000 Subject: Re: [lm-sensors] [PATCH v2] linux/kernel.h: Fix DIV_ROUND_CLOSEST with unsigned divisors Message-Id: <20121219134721.bbde212f.akpm@linux-foundation.org> List-Id: References: <1355928015-26212-1-git-send-email-linux@roeck-us.net> In-Reply-To: <1355928015-26212-1-git-send-email-linux@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Guenter Roeck Cc: linux-kernel@vger.kernel.org, lm-sensors@lm-sensors.org, Juergen Beisert , Jean Delvare On Wed, 19 Dec 2012 06:40:15 -0800 Guenter Roeck wrote: > Commit 263a523 fixes a warning seen with W=1 due to change in > DIV_ROUND_CLOSEST. Unfortunately, the C compiler converts divide operations > with unsigned divisors to unsigned, even if the dividend is signed and > negative (for example, -10 / 5U = 858993457). The C standard says "If one > operand has unsigned int type, the other operand is converted to unsigned > int", so the compiler is not to blame. > As a result, DIV_ROUND_CLOSEST(0, 2U) and similar operations now return > bad values, since the automatic conversion of expressions such as "0 - 2U/2" > to unsigned was not taken into account. > > Fix by checking for the divisor variable type when deciding which operation > to perform. This fixes DIV_ROUND_CLOSEST(0, 2U), but still returns bad values > for negative dividends divided by unsigned divisors. Mark the latter case as > unsupported. The changelog didn't describe the end-user visible effects of the bug. Please always include this information. Because... The patch is applicable to 3.7.x. Should we backport it? _______________________________________________ lm-sensors mailing list lm-sensors@lm-sensors.org http://lists.lm-sensors.org/mailman/listinfo/lm-sensors