linux-kernel - Re: [PATCH v3] ktime: Fix ktime

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Date:	Tue, 12 May 2015 16:14:52 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	John Stultz <john.stultz@...aro.org>
cc:	lkml <linux-kernel@...r.kernel.org>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Ingo Molnar <mingo@...nel.org>,
	Josh Boyer <jwboyer@...hat.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Trevor Cordes <trevor@...nopolis.ca>, stable@...r.kernel.org
Subject: Re: [PATCH v3] ktime: Fix ktime_divns to do signed division

On Fri, 8 May 2015, John Stultz wrote:
> +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);

This triggers the typecheck for u64 in do_div(). The delta patch below
should do the trick.

Thanks,

	tglx

diff --git a/include/linux/ktime.h b/include/linux/ktime.h
index ab2de1c7932c..b9620ebe356f 100644
--- a/include/linux/ktime.h
+++ b/include/linux/ktime.h
@@ -177,13 +177,13 @@ static inline s64 ktime_divns(const ktime_t kt, s64 div)
 	if (__builtin_constant_p(div) && !(div >> 32)) {
 		s64 ns = kt.tv64;
 		int neg = (ns < 0);
+		u64 tmp;
 
 		if (neg)
 			ns = -ns;
-		do_div(ns, div);
-		if (neg)
-			ns = -ns;
-		return ns;
+		tmp = ns;
+		do_div(tmp, div);
+		return neg ? -tmp : tmp;
 	} else {
 		return __ktime_divns(kt, div);
 	}
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index c98ce4d9f613..bac65f810afd 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -268,8 +268,9 @@ lock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
  */
 s64 __ktime_divns(const ktime_t kt, s64 div)
 {
-	s64 dclc;
 	int neg, sft = 0;
+	s64 dclc;
+	u64 tmp;
 
 	dclc = ktime_to_ns(kt);
 	neg = (dclc < 0);
@@ -280,12 +281,9 @@ s64 __ktime_divns(const ktime_t kt, s64 div)
 		sft++;
 		div >>= 1;
 	}
-	dclc >>= sft;
-	do_div(dclc, (unsigned long) div);
-	if (neg)
-		dclc = -dclc;
-
-	return dclc;
+	tmp = dclc >> sft;
+	do_div(tmp, (unsigned long) div);
+	return neg ? -tmp : tmp;
 }
 EXPORT_SYMBOL_GPL(__ktime_divns);
 #endif /* BITS_PER_LONG >= 64 */
--
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