On Tue, May 12, 2015 at 7:14 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> 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.
>
I started looking into this, and this landed in my inbox. Thanks Thomas! :)
I reproduced the issue w/ the kbuildbot instructions and the patch
below resolves it.
Acked-by: John Stultz <john.stultz@xxxxxxxxxx>
> 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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