Messages in this thread | | | From | Neeraj Upadhyay <> | Subject | Query regarding __hrtimer_get_next_event() | Date | Thu, 26 Oct 2017 14:34:29 +0530 |
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Hi,
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.
static ktime_t __hrtimer_get_next_event(...) { <snip> for (; active; base++, active >>= 1) {
<snip> timer = container_of(next, struct hrtimer, node); expires = ktime_sub(hrtimer_get_expires(timer), base->offset); if (expires.tv64 < expires_next.tv64) { expires_next = expires; hrtimer_update_next_timer(cpu_base, timer); } } <snip> if (expires_next.tv64 < 0) expires_next.tv64 = 0; return expires_next; }
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?
expires = ktime_sub(hrtimer_get_expires(timer), base->offset); + /* + * if expires is a very high positive value and base->offset is + * negative, expires can overflow and get negative value. Set + * expires to KTIME_MAX, if we encounter this. + */ + if (hrtimer_get_expires(timer).tv64 > 0 && + base->offset.tv64 < 0 && expires.tv64 < 0) + expires.tv64 = KTIME_MAX; +
Thanks Neeraj
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