From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751613AbbEFTmK (ORCPT ); Wed, 6 May 2015 15:42:10 -0400 Received: from mail-pd0-f178.google.com ([209.85.192.178]:35412 "EHLO mail-pd0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750812AbbEFTmG (ORCPT ); Wed, 6 May 2015 15:42:06 -0400 From: John Stultz To: linux-kernel@vger.kernel.org Cc: John Stultz , Nicolas Pitre , Thomas Gleixner , Josh Boyer , One Thousand Gnomes , Trevor Cordes Subject: [RFC][PATCH v2] ktime: Fix ktime_divns to do signed division Date: Wed, 6 May 2015 12:41:55 -0700 Message-Id: <1430941315-18005-1-git-send-email-john.stultz@linaro.org> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It was noted that the 32bit implementation of ktime_divns() was doing unsigned division and didn't properly handle negative values. This patch fixes the problem by checking and preserving the sign bit, and then reapplying it if appropriate after the division, it also changes the return type to a s64 to make it more obvious this is expected. Nicolas also pointed out that negative dividers would cause infinite loops on 32bit systems, negative dividers is unlikely for users of this function, but out of caution this patch adds BUG_ON checks for negative dividers in both the 32 and 64bit versions to make sure no such use cases creep in. Cc: Nicolas Pitre Cc: Thomas Gleixner Cc: Josh Boyer Cc: One Thousand Gnomes Cc: Trevor Cordes Tested-by: Trevor Cordes Reported-by: Trevor Cordes Signed-off-by: John Stultz --- include/linux/ktime.h | 27 +++++++++++++++++++++++---- kernel/time/hrtimer.c | 11 ++++++++--- 2 files changed, 31 insertions(+), 7 deletions(-) diff --git a/include/linux/ktime.h b/include/linux/ktime.h index 5fc3d10..ac9359e 100644 --- a/include/linux/ktime.h +++ b/include/linux/ktime.h @@ -166,19 +166,38 @@ static inline bool ktime_before(const ktime_t cmp1, const ktime_t cmp2) } #if BITS_PER_LONG < 64 -extern u64 __ktime_divns(const ktime_t kt, s64 div); -static inline u64 ktime_divns(const ktime_t kt, s64 div) +extern s64 __ktime_divns(const ktime_t kt, s64 div); +static inline s64 ktime_divns(const ktime_t kt, s64 div) { + /* + * Negative divisors could cause an inf loop, + * so bug out here. + */ + BUG_ON(div < 0); if (__builtin_constant_p(div) && !(div >> 32)) { - u64 ns = kt.tv64; + s64 ns = kt.tv64; + int neg = (ns < 0); + + if (neg) + ns = -ns; do_div(ns, div); + if (neg) + ns = -ns; return ns; } else { return __ktime_divns(kt, div); } } #else /* BITS_PER_LONG < 64 */ -# define ktime_divns(kt, div) (u64)((kt).tv64 / (div)) +static inline s64 ktime_divns(const ktime_t kt, s64 div) +{ + /* + * 32-bit implementation cannot handle negative divisors, + * so catch them on 64bit as well. + */ + BUG_ON(div < 0); + return (u64)((kt).tv64 / (div)) +} #endif static inline s64 ktime_to_us(const ktime_t kt) diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index 76d4bd9..c98ce4d 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -266,12 +266,15 @@ lock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags) /* * Divide a ktime value by a nanosecond value */ -u64 __ktime_divns(const ktime_t kt, s64 div) +s64 __ktime_divns(const ktime_t kt, s64 div) { - u64 dclc; - int sft = 0; + s64 dclc; + int neg, sft = 0; dclc = ktime_to_ns(kt); + neg = (dclc < 0); + if (neg) + dclc = -dclc; /* Make sure the divisor is less than 2^32: */ while (div >> 32) { sft++; @@ -279,6 +282,8 @@ u64 __ktime_divns(const ktime_t kt, s64 div) } dclc >>= sft; do_div(dclc, (unsigned long) div); + if (neg) + dclc = -dclc; return dclc; } -- 1.9.1