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SubjectRe: [PATCH] ktime_add_ns() may overflow on 32bit architectures
On 03/19/2013 05:29 AM, David Engraf wrote:
> Hello,
>
> I've triggered an overflow when using ktime_add_ns() on a 32bit
> architecture not supporting CONFIG_KTIME_SCALAR.
>
> When passing a very high value for u64 nsec, e.g. 7881299347898368000
> the do_div() function converts this value to seconds (7881299347)
> which is still to high to pass to the ktime_set() function as long.
> The result in my case is a negative value.
>
> The problem on my system occurs in the tick-sched.c,
> tick_nohz_stop_sched_tick() when time_delta is set to
> timekeeping_max_deferment(). The check for time_delta < KTIME_MAX is
> valid, thus ktime_add_ns() is called with a too large value resulting
> in a negative expire value. This leads to an endless loop in the
> ticker code:
>
> time_delta: 7881299347898368000
> expires = ktime_add_ns(last_update, time_delta)
> expires: negative value
>
> This error doesn't occurs on 64bit or architectures supporting
> CONFIG_KTIME_SCALAR (e.g. ARM, x86-32).

Sorry, this fell through the cracks. I see Andrew caught it, but I've
queued for 3.10 in my tree as well.

This should be tagged for -stable as well, no?

thanks
-john



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