lkml.org 
[lkml]   [2017]   [Oct]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectQuery regarding __hrtimer_get_next_event()
Date
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

--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member of the Code Aurora Forum, hosted by The Linux Foundation

\
 
 \ /
  Last update: 2017-10-26 11:04    [W:0.044 / U:1.892 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site