2015-12-03 19:04 GMT+03:00 Sasha Levin <[email protected]>: > On 12/03/2015 10:39 AM, Andrey Ryabinin wrote: >> 2015-12-03 18:30 GMT+03:00 Sasha Levin <[email protected]>: >>> > Passing 0 to roundup_pow_of_two would lead to wrapping around and trying >>> > to >>> > find the last set bit on (unsigned long)(-1), which is obviously wrong. >>> > >>> > Instead, deal with this case by rounding it up to the closest power of two >>> > (2 ** 0). >>> > >>> > Signed-off-by: Sasha Levin <[email protected]> >>> > --- >>> > include/linux/log2.h | 3 +++ >>> > 1 file changed, 3 insertions(+) >>> > >>> > diff --git a/include/linux/log2.h b/include/linux/log2.h >>> > index fd7ff3d..b6bdf0c 100644 >>> > --- a/include/linux/log2.h >>> > +++ b/include/linux/log2.h >>> > @@ -60,6 +60,9 @@ bool is_power_of_2(unsigned long n) >>> > static inline __attribute__((const)) >>> > unsigned long __roundup_pow_of_two(unsigned long n) >>> > { >>> > + if (n == 0) >>> > + return 1UL << 0; >>> > + >> Perhaps we should fix callers instead? >> Comment near roundup_pow_of_two() says that result is undefined when n == 0: > > That's how I've started doing it, but when it showed up with 3 different > callers > I figured it's better to fix it at the source. > > This fix would return a valid value and is working fine with the callers. >
In that case patch should update the comment. > Thanks, > Sasha -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
