Messages in this thread | | | Subject | Re: Query regarding __hrtimer_get_next_event() | From | Neeraj Upadhyay <> | Date | Thu, 26 Oct 2017 19:53:22 +0530 |
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Hi tglx,
Forgot to mention, we are using kernel stable version 3.18 https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/tree/kernel/time/timekeeping.c?h=v3.18.77
wall time is being set to a value close to epoch but less than epoch + current uptime.
Looks like https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/kernel/time?id=e1d7ba8735551ed79c7a0463a042353574b96da3
handles this case, but is not present in 3.18 tree. We will try by pulling this patch to 3.18 tree.
int do_settimeofday(const struct timespec *tv) { xt = tk_xtime(tk); ts_delta.tv_sec = tv->tv_sec - xt.tv_sec; ts_delta.tv_nsec = tv->tv_nsec - xt.tv_nsec;
<snip> tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, ts_delta)); }
xt = ( tv_sec = 1508807131, tv_nsec = 223767601) 2017/10/24 9:5:31
tk->wall_to_monotonic = ( tv_sec = -1508803094, tv_nsec = 15152092)
ts_delta = (tv_sec = -1508803200, tv_nsec = -767601)
wall_to_monotonic is bigger than the ts_delta, so leading to wall_to_monotonic become positive value, resulting in -ve off_real.
Thanks Neeraj
On 10/26/2017 06:27 PM, Thomas Gleixner wrote: > 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
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