The patch titled Subject: linux/kernel.h: fix DIV_ROUND_CLOSEST with unsigned divisors has been added to the -mm tree. Its filename is linux-kernelh-fix-div_round_closest-with-unsigned-divisors.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Guenter Roeck <linux@xxxxxxxxxxxx> Subject: linux/kernel.h: fix DIV_ROUND_CLOSEST with unsigned divisors Commit 263a523 ("linux/kernel.h: Fix warning seen with W=1 due to change in DIV_ROUND_CLOSEST") 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. Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx> Reported-by: Juergen Beisert <jbe@xxxxxxxxxxxxxx> Tested-by: Juergen Beisert <jbe@xxxxxxxxxxxxxx> Cc: Jean Delvare <khali@xxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/kernel.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff -puN include/linux/kernel.h~linux-kernelh-fix-div_round_closest-with-unsigned-divisors include/linux/kernel.h --- a/include/linux/kernel.h~linux-kernelh-fix-div_round_closest-with-unsigned-divisors +++ a/include/linux/kernel.h @@ -77,13 +77,15 @@ /* * Divide positive or negative dividend by positive divisor and round - * to closest integer. Result is undefined for negative divisors. + * to closest integer. Result is undefined for negative divisors and + * for negative dividends if the divisor variable type is unsigned. */ #define DIV_ROUND_CLOSEST(x, divisor)( \ { \ typeof(x) __x = x; \ typeof(divisor) __d = divisor; \ - (((typeof(x))-1) > 0 || (__x) > 0) ? \ + (((typeof(x))-1) > 0 || \ + ((typeof(divisor))-1) > 0 || (__x) > 0) ? \ (((__x) + ((__d) / 2)) / (__d)) : \ (((__x) - ((__d) / 2)) / (__d)); \ } \ _ Patches currently in -mm which might be from linux@xxxxxxxxxxxx are origin.patch linux-next.patch linux-kernelh-fix-div_round_closest-with-unsigned-divisors.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html