Re: [Qemu-devel] Fedora FC21 - Bug: 100% CPU and hangs in gettimeofday(&tp, NULL); forever

[Gerhard Wiesinger]

On 13.01.2015 21:48, Paolo Bonzini wrote:
> On 13/01/2015 21:13, Gerhard Wiesinger wrote:
> > It happens also with qemu-kvm 2.2.0 on another VM where also PostgreSQL
> > is running:
> > (gdb) bt
> > #0  0x00007fff9a1feff4 in gettimeofday ()
> > #1  0x00000000006d425e in GetCurrentTimestamp () at timestamp.c:1274
> >
> > What we know:
> > OK : F20: 3.17.6-200.fc20.x86_64 on guest/host,
> > qemu-kvm-1.6.2-10.fc20.x86_64 on host
> > NOK: F21: 3.17.7-300.fc21.x86_64 on guest/host,
> > qemu-kvm-2.1.2-7.fc21.x86_64 on host
> > NOK: F21: 3.17.8-300.fc21.x86_64 on guest/host,
> > qemu-kvm-2.2.0-1.fc21.x86_64 on host
> >
> > No one less can reproduce or has similar problems?
> > Any further ideas?
> Hmm, too bad. :(
>
> Any chance you can try with 1.7 and 2.0 releases?  Cole, perhaps you
> help building some RPMS for Gerhard?

Yes, I can try. RPMs would be fine.

Don't know if it is related, but on another VM maschine I was getting 
the following 75s after reboot:
[   78.857006] INFO: rcu_sched self-detected stall on CPU { 0} (t=60000 
jiffies g=1966 c=1965 q=0)
[  258.860006] INFO: rcu_sched self-detected stall on CPU { 0} (t=240003 
jiffies g=1966 c=1965 q=0)

I also had a look at the kernel code again:
http://lxr.free-electrons.com/source/kernel/time/timekeeping.c?v=3.17#L493
499         do {
500                 seq = read_seqcount_begin(&tk_core.seq);
501
502                 ts->tv_sec = tk->xtime_sec;
503                 nsecs = timekeeping_get_ns(&tk->tkr);
504
505         } while (read_seqcount_retry(&tk_core.seq, seq));

So it looks like that the seqcount always changes and therefore loops 
forever here (as far as I digged it down this is the only loop here).

Might be something wrong with the memory barriers in recent qemu-kvm 
releases?

Ciao,
Gerhard