Re: Query regarding __hrtimer_get_next_event()

[Thomas Gleixner <tglx@linutronix.de>]

On Thu, 26 Oct 2017, Neeraj Upadhyay wrote:
> We have one query regarding the __hrtimer_get_next_event().
> The expires_next.tv64 is set to 0 if it is < 0. We observed
> an hrtimer interrupt storm for one of the hrtimers with
> below properties:
> 
> * Expires for the hrtimer was set to KTIME_MAX.
> * cpu base was HRTIMER_BASE_REALTIME with negative base->offset.
> * Due to below sub, expires overflowed to a negative value and
>   expires_next.tv64 was set to 0
>     expires = ktime_sub(hrtimer_get_expires(timer), base->offset);
> * Due to this, clockevent was programmed to min_delta_ns, everytime
>   as __hrtimer_get_next_event() returned 0.
> 
> 
> This may not be a valid use case (queuing a hrtimer with KTIME_MAX)
> expires, but should we guard the hrtimer next event code against
> this by using KTIME_MAX upper bound. Is something like below a
> proper way to guard it? Or am I missing something here?

Can you please explain how you managed to have a negative base->offset?

Thanks,

	tglx