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Re: [Qemu-devel] qemu-kvm-1.0 crashes with threaded vnc server?

From: Peter Lieven
Subject: Re: [Qemu-devel] qemu-kvm-1.0 crashes with threaded vnc server?
Date: Tue, 26 Jun 2012 17:02:13 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20110921 Thunderbird/3.1.15

On 13.03.2012 16:06, Alexander Graf wrote:
On 13.03.2012, at 16:05, Corentin Chary wrote:

On Tue, Mar 13, 2012 at 12:29 PM, Peter Lieven<address@hidden>  wrote:
On 11.02.2012 09:55, Corentin Chary wrote:
On Thu, Feb 9, 2012 at 7:08 PM, Peter Lieven<address@hidden>   wrote:

is anyone aware if there are still problems when enabling the threaded
I saw some VMs crashing when using a qemu-kvm build with

qemu-kvm-1.0[22646]: segfault at 0 ip 00007fec1ca7ea0b sp
error 6 in libz.so.[7fec1ca75000+16000]
qemu-kvm-1.0[26056]: segfault at 7f06d8d6e010 ip 00007f06e0a30d71 sp
00007f06df035748 error 6 in libc-2.11.1.so[7f06e09aa000+17a000]

I had no time to debug further. It seems to happen shortly after
but thats uncertain. At least the segfault in libz seems to
give a hint to VNC since I cannot image of any other part of qemu-kvm
libz except for VNC server.


Hi Peter,
I found two patches on my git tree that I sent long ago but somehow
get lost on the mailing list. I rebased the tree but did not have the
time (yet) to test them.
Feel free to try them. If QEMU segfault again, please send a full gdb
backtrace / valgrind trace / way to reproduce :).

I have seen no more crashes with these to patches applied. I would suggest
it would be good to push them to the master repository.

Thank you,

Ccing Alexander,
Ah, cool. Corentin, I think you're right now the closest thing we have to a 
maintainer for VNC. Could you please just send out a pull request for those?
hi all,

i suspect there is still a problem with the threaded vnc server. its just a guess, but we saw a resonable number of vms hanging in the last weeks. hanging meaning the emulation is stopped and the qemu-kvm process does no longer react, not on monitor, not on vnc, not on qmp. why i suspect the threaded vnc server is that in all cases we have analyzed this happened with an open vnc session and only on nodes with the threaded vnc server enabled. it might also be the case that this happens at a resolution change. is there anything known or has someone an idea?

we are running qemu-kvm 1.0.1 with

  vnc: don't mess up with iohandlers in the vnc thread

  vnc: Limit r/w access to size of allocated memory

compiled in.

unfortunately, i was not yet able to reproduce this with a debugger attached.



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