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

[Gerhard Wiesinger]

Hello,

After upgrading my KVM environment from Fedora 20 to Fedora 21 up2date 
(hosts and guests, Intel CPU) I've the following problem:
1.) On the database VM PostgresSQL e.g. 2 processes hang with 100% cpu
2.) On the monitoring VM Munin/RRDtool also hangs with 100% cpu
Killing of processes is not possible, only reboot helps.

But I nailed it down to the following:
yum install strace
strace -y -p339
Process 339 attached
# no system calls here
^CProcess 339 detached

Going deeper:
yum --enablerepo fedora-debuginfo,updates-debuginfo install gdb 
postgresql-debuginfo
gdb postgres 339
(gdb) bt
#0  0x00007fffffbf8ff8 in gettimeofday ()
#1  0x00000000006d425e in GetCurrentTimestamp () at timestamp.c:1274
(gdb) frame 1
#1  0x00000000006d425e in GetCurrentTimestamp () at timestamp.c:1274
1274            gettimeofday(&tp, NULL);
(same on second process here)

Quitting and reattaching gdb also hangs here, so gettimeofday takes 100% 
CPU and never ends!

Therefore I guess this is a problem either in the Linux kernel or in 
QEMU/KVM.
It might be the case that something changed in timer handling or some 
default changed here. VMs are time syncrhonized with NTP so this might 
also be a problem that the syscall hangs here.

Workaround when it happens: reboot ....

Any further ideas?

Thank you.

Ciao,
Gerhard