Re: [uml-devel] [UM] Long loop in __getnsdayoftime() after resume from ram

[Richard Weinberger]

On Fri, Apr 24, 2015 at 9:58 PM, Thomas Meyer <thomas@xxxxxxxx> wrote:
> Am Montag, den 20.10.2014, 11:56 +0200 schrieb Richard Weinberger:
>> Am 20.10.2014 um 11:51 schrieb Thomas Meyer:
>> >> Hmm, does this always happen?
>> >
>> > Yes, my single core system seems to trigger this every time after resume from ram.
>>
>> What is your host kernel?
>>
>> >> At least on my notebook it did not happen. I've started an UML yesterday
>> >> suspended it and after more than 12h it worked fine today.
>> >>
>> >> BTW: Do you see the issue also then freezing UML using the freezer cgroup?
>> >
>> > I'm not sure what do you mean by this. Do I need to enable some special configs for this in the host or uml kernel?
>>
>> Create on the host side a new freezer cgroup, put UML into it and freeze/thaw it.
>> i.e. mkdir /sys/fs/cgroup/freezer/uml ; echo <pid of a shell> >  /sys/fs/cgroup/freezer/uml/tasks.
>> In the said shell run UML and then freeze it using echo FROZEN > /sys/fs/cgroup/freezer/uml/freezer.state.
>> Later thaw it: echo THAWED > /sys/fs/cgroup/freezer/uml/freezer.state
>>
>
> Sadly, this also happens with a cgroup freezer group :-(
>
> bt
> #0  __iter_div_u64_rem (remainder=<optimized out>, divisor=<optimized out>, dividend=14641577537827850536) at include/linux/math64.h:12
> 7
> #1  timespec_add_ns (ns=<optimized out>, a=<optimized out>) at include/linux/time.h:235
> #2  __getnstimeofday64 (ts=0xffffffffffffffff) at kernel/time/timekeeping.c:658
> #3  0x0000000060098a00 in getnstimeofday64 (ts=<optimized out>) at kernel/time/timekeeping.c:678
> #4  0x0000000060098a4c in do_gettimeofday (tv=0xab359e50) at kernel/time/timekeeping.c:897
> #5  0x0000000060090d66 in SYSC_gettimeofday (tz=<optimized out>, tv=<optimized out>) at kernel/time/time.c:107
> #6  SyS_gettimeofday (tv=-1, tz=2097152000) at kernel/time/time.c:102
> #7  0x0000000060032cf3 in handle_syscall (r=0xa39db9e8) at arch/um/kernel/skas/syscall.c:35
> #8  0x000000006004a247 in handle_trap (local_using_sysemu=<optimized out>, regs=<optimized out>, pid=<optimized out>) at arch/um/os-Lin
> ux/skas/process.c:174
> #9  userspace (regs=0xa39db9e8) at arch/um/os-Linux/skas/process.c:399
> #10 0x000000006002f125 in fork_handler () at arch/um/kernel/process.c:149
> #11 0x0000000000000000 in ?? ()
>
> It seems as only very few people running UML kernels and suspend their host systems...
>
> Any ideas?

Can you give the attached patch a try?
Let's see if it proves my theory.
Looks like UML's clocksource needs fixing.
-- 
Thanks,
//richard
diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c
index 117568d..3936948 100644
--- a/arch/um/kernel/time.c
+++ b/arch/um/kernel/time.c
@@ -67,14 +67,14 @@ static irqreturn_t um_timer(int irq, void *dev)
 
 static cycle_t itimer_read(struct clocksource *cs)
 {
-	return os_nsecs() / 1000;
+	return os_nsecs();
 }
 
 static struct clocksource itimer_clocksource = {
 	.name		= "itimer",
 	.rating		= 300,
 	.read		= itimer_read,
-	.mask		= CLOCKSOURCE_MASK(64),
+	.mask		= CLOCKSOURCE_MASK(32),
 	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
 };
 
@@ -92,7 +92,7 @@ static void __init setup_itimer(void)
 		clockevent_delta2ns(60 * HZ, &itimer_clockevent);
 	itimer_clockevent.min_delta_ns =
 		clockevent_delta2ns(1, &itimer_clockevent);
-	err = clocksource_register_hz(&itimer_clocksource, USEC_PER_SEC);
+	err = clocksource_register_hz(&itimer_clocksource, NSEC_PER_SEC);
 	if (err) {
 		printk(KERN_ERR "clocksource_register_hz returned %d\n", err);
 		return;