Re: [PATCH v3] ktime: Fix ktime_divns to do signed division

[Thomas Gleixner]

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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