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

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Date:	Fri, 24 Apr 2015 21:58:40 +0200
From:	Thomas Meyer <thomas@...3r.de>
To:	Richard Weinberger <richard@....at>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	user-mode-linux-devel <user-mode-linux-devel@...ts.sourceforge.net>
Subject: Re: [uml-devel] [UM] Long loop in __getnsdayoftime() after resume
 from ram

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?

I'll go with this patch so long:
diff --git a/include/linux/time.h b/include/linux/time.h
index beebe3a..3486050 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -232,7 +232,7 @@ extern struct timeval ns_to_timeval(const s64 nsec);
  */
 static __always_inline void timespec_add_ns(struct timespec *a, u64 ns)
 {
-       a->tv_sec += __iter_div_u64_rem(a->tv_nsec + ns, NSEC_PER_SEC, &ns);
+       a->tv_sec += div_u64_rem(a->tv_nsec + ns, NSEC_PER_SEC, &ns);
        a->tv_nsec = ns;
 }

kind regards
thomas

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