ktime: Fix ktime_divns to do signed division (f7bcb70e) · Commits · 戴 / test

It was noted that the 32bit implementation of ktime_divns() was doing unsigned division and didn't properly handle negative values. And when a ktime helper was changed to utilize ktime_divns, it caused a regression on some IR blasters. See the following bugzilla for details: https://bugzilla.redhat.com/show_bug.cgi?id=1200353 This patch fixes the problem in ktime_divns 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 checks for negative dividers for both 32-bit (BUG_ON) and 64-bit(WARN_ON) versions to make sure no such use cases creep in. [ tglx: Hand an u64 to do_div() to avoid the compiler warning ] Fixes: 'ktime: Sanitize ktime_to_us/ms conversion' Reported-and-tested-by:

Trevor Cordes <trevor@tecnopolis.ca> Signed-off-by:

John Stultz <john.stultz@linaro.org> Acked-by:

Nicolas Pitre <nicolas.pitre@linaro.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Josh Boyer <jwboyer@redhat.com> Cc: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/1431118043-23452-1-git-send-email-john.stultz@linaro.org Signed-off-by:

Thomas Gleixner <tglx@linutronix.de>

include/linux/ktime.h

+21 −6

Original line number	Diff line number	Diff line
		@@ -166,19 +166,34 @@ 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;
		do_div(ns, div);
		return ns;
		s64 ns = kt.tv64;
		u64 tmp = ns < 0 ? -ns : ns;

		do_div(tmp, div);
		return ns < 0 ? -tmp : tmp;
		} 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.
		*/
		WARN_ON(div < 0);
		return kt.tv64 / div;
		}
		#endif

		static inline s64 ktime_to_us(const ktime_t kt)

kernel/time/hrtimer.c

+8 −6

Original line number	Diff line number	Diff line
		@@ -266,21 +266,23 @@ 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;
		u64 tmp;

		dclc = ktime_to_ns(kt);
		tmp = dclc < 0 ? -dclc : dclc;

		/* Make sure the divisor is less than 2^32: */
		while (div >> 32) {
		sft++;
		div >>= 1;
		}
		dclc >>= sft;
		do_div(dclc, (unsigned long) div);

		return dclc;
		tmp >>= sft;
		do_div(tmp, (unsigned long) div);
		return dclc < 0 ? -tmp : tmp;
		}
		EXPORT_SYMBOL_GPL(__ktime_divns);
		#endif /* BITS_PER_LONG >= 64 */

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