[Qemu-devel] Re: [PATCH] vnc: threaded server depends on io-thread

[Jan Kiszka]

On 2011-03-09 12:05, Stefan Hajnoczi wrote:
> On Wed, Mar 9, 2011 at 10:57 AM, Corentin Chary
> <address@hidden> wrote:
>>>> The threaded VNC servers messed up with QEMU fd handlers without
>>>> any kind of locking, and that can cause some nasty race conditions.
>>>>
>>>> The IO-Thread provides appropriate locking primitives to avoid that.
>>>> This patch makes CONFIG_VNC_THREAD depends on CONFIG_IO_THREAD,
>>>> and add lock and unlock calls around the two faulty calls.
>>>
>>> qemu-kvm currently doesn't compile with --enable-io-thread. is there an 
>>> easy fix
>>> for this?
>>
>> If IO Thread is not available, I'm afraid that --disable-vnc-thread is
>> the only fix.
>> Or, you can try to define some global mutex acting like iothread
>> locks, but that doesn't sounds like an easy fix.
> 
> Jan or Marcelo can help here but qemu-kvm has an iothread equivalent
> built in by default.  It should be possible to use that.

qemu_mutex_lock/unlock_iothread is properly provided in qemu-kvm even
without --enable-io-thread. So that tree could temporarily disable the
new configure check until we got rid of the special qemu-kvm bits.
Corentin's patch is against upstream, that adjustment need to be made
once the commit is merged into qemu-kvm.

Jan

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