Dear experts,
When i was running cyclictest with ltp(kernel 4.19.90 rt, arch64),
cyclictest got a big latecy(more than 10ms), the ftrace log shows that
modprobe called preempt_disable for a long time, which stops cyclictest
being switched.
here is a piece of log:
modprobe-4551 0...10 712.754529: preempt_disable:
caller=0xffff0001019900c8 parent=0xffff0001019900c8
...
modprobe-4551 0d..10 712.754589: irq_disable: caller=el1_irq+0x7c
parent=0xffff0001019900dc
modprobe-4551 0d.h10 712.754590: irq_handler_entry: irq=2
name=arch_timer
modprobe-4551 0d.h20 712.754591: hrtimer_cancel:
hrtimer=0xffff8020f4983d98
modprobe-4551 0d.h10 712.754591: hrtimer_expire_entry:
hrtimer=0xffff8020f4983d98 now=712720218245 function=hrtimer_wakeup/0x0
modprobe-4551 0d.h20 712.754592: sched_waking: comm=cyclictest
pid=2212 prio=9 target_cpu=000
modprobe-4551 0dNh30 712.754593: sched_wakeup: cyclictest:2212 [9]
success=1 CPU:000
modprobe-4551 0dNh10 712.754594: hrtimer_expire_exit:
hrtimer=0xffff8020f4983d98
modprobe-4551 0dNh10 712.754594: irq_handler_exit: irq=2
ret=handled
Further i found
preemptirq_delay_test(kernel/trace/preemptirq_delay_test.c) can
reproduce it easily and got the similar ftrace log.
The root cause i found is in el1_irq, it checks preempt count and
TIF_NEED_RESCHED before it goes through the path el1_preempt,
preempt_disable just stops it happening.
Then i came up an idea and did an experiment, call
preempt_count_set(0); and set_tsk_need_resched(task); in hrtimer_wakeup
to meet the expectation in order to reschdule.
static enum hrtimer_restart hrtimer_wakeup(struct hrtimer *timer)
{
struct hrtimer_sleeper *t =
container_of(timer, struct hrtimer_sleeper, timer);
struct task_struct *task = t->task;
t->task = NULL;
if (task)
wake_up_process(task);
if(preempt_count())
preempt_count_set(0);
set_tsk_need_resched(task);
return HRTIMER_NORESTART;
}
but, failed, system froze, no panic information.
Is there anyone having the same problem? i would appreciate it if you
could share me some information in this case, many thanks.
BR
Song Chen
