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

[Gerhard Wiesinger <lists@wiesinger.com>]

On 14.01.2015 10:15, Gerhard Wiesinger wrote:
> On 14.01.2015 01:59, Laine Stump wrote:
>>
>> Take a look at the following kernel bug. It specifically deals with a
>> hang in gettimeofday() in a KVM guest:
>>
>> https://bugzilla.redhat.com/show_bug.cgi?id=1178975
>>
>> There is a link to a patched kernel you can try; it fixed my problems (I
>> was repeatedly getting hangs in python-urlgrabber during yum updates on
>> F21).
>>
>
> Looks to be fixed, commented in:
> https://bugzilla.redhat.com/show_bug.cgi?id=1178975
> Installed kernels.
> http://koji.fedoraproject.org/koji/taskinfo?taskID=8575247
>

There seems to be another problem. My PostgreSQL server VM still crashes 
(2 times).
1.) First time crash: no reaction at all in KVM console, no network access
2.) Second time "crash":
- KVM console 2 characters could be entered, then console was dead forever
- ping works
- ssh not
- host: 100% cpu on 2 cores
strace -y -p on kvm host (loops through this):
read(7<anon_inode:[eventfd]>, 0x7fffb862bf20, 16) = -1 EAGAIN (Resource 
temporarily unavailable)
ioctl(11<anon_inode:kvm-vm>, KVM_GET_DIRTY_LOG, 0x7fffb862bd30) = 0
ioctl(11<anon_inode:kvm-vm>, KVM_GET_DIRTY_LOG, 0x7fffb862bd30) = 0
write(6<anon_inode:[eventfd]>, "\1\0\0\0\0\0\0\0", 8) = 8
ppoll([{fd=98<socket:[4660317]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=89<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=88<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=87<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=86<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=85<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=84<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=83<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=82<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=81<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=80<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=79<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=78<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=77<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=76<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=75<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=74<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=73<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=72<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=71<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=70<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=69<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=68<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=67<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=66<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=65<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=64<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=63<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=62<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=61<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=60<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, 
{fd=59<anon_inode:[eventfd]>, events=POLLIN|POLLERR|POLLHUP}, ...], 71, 
{0, 124112228}, NULL, 8) = 1 ([...], left {0, 124090614})
write(7<anon_inode:[eventfd]>, "\1\0\0\0\0\0\0\0", 8) = 8
read(6<anon_inode:[eventfd]>, "\1\0\0\0\0\0\0\0", 512) = 8
write(7<anon_inode:[eventfd]>, "\1\0\0\0\0\0\0\0", 8) = 8

Kernel (host/guest):  3.18.6-200.fc21.x86_64 #1 SMP
qemu-kvm-2.2.0-5.fc21.x86_64

Bug 1178975 - endless loop in clock_gettime() on a kvm-based VM
https://bugzilla.redhat.com/show_bug.cgi?id=1178975
is fixed (didn't occour with the test program posted at 
https://bugzilla.redhat.com/show_bug.cgi?id=1178975#c28 in 30min, 
happened before reproduceable in 2min, still running)

So I guess there is another problem in the kernel with volatile and gcc 
optimizations (or maybe in qemu-KVM)

Any ideas?
Any other bug reports like this?

Thank you.

Ciao,
Gerhard

-- http://www.wiesinger.com/