[libvirt] virNetClientPtr leak in remote driver

[Matthias Bolte]

2011/8/1 Eric Blake <eblake at redhat.com>:
> On 07/28/2011 12:07 PM, Matthias Bolte wrote:
>> 2011/7/27 Matthias Bolte <matthias.bolte at googlemail.com>:
>>> doRemoteClose doesn't free the virNetClientPtr and this creates a
>>> 260kb leak per remote connection. This happens because
>>> virNetClientFree doesn't remove the last ref, because virNetClientNew
>>> creates the virNetClientPtr with a refcount of 2.
>>>
>
>> The memory leak I saw was due to virsh calling
>> virEventRegisterDefaultImpl, but not calling virEventRunDefaultImpl.
>> Because the event loop is initialized, the call to
>> virNetSocketAddIOCallback in virNetClientNew succeeds. But virsh not
>> driving the event loop results in not removing callbacks that were
>> marked for deletion. Finally this leaks the virNetClientPtr using in
>> the remote driver. I used a virsh -c qemu:///system to test.
>>
>> I was able fix this by calling virEventRunDefaultImpl after
>> virConnectClose in virsh. But I don't think that this is the correct
>> general solution.
>
> Where do we stand with 0.9.4?  Is this something where we need the
> general fix before the release, or is just the virsh hack to call
> virEventRunDefaultImpl good enough for the release, or is this problem
> not severe enough and we can release as-is?

virsh is a bit special here as it registers/initializes the default
even loop but doesn't drive it properly. It only drives it for the
console command. That's the problem in virsh. This can be avoided by
calling virEventRunDefaultImpl after virConnectClose iff it's a remote
connection, in other cases virEventRunDefaultImpl might block.
Therefore, we shouldn't be calling it in general after a
virConnectClose in virsh.

If we assume that an application that registers an event loop will
drive it properly then this problem is not critical, as it doesn't
exist. Just virsh is a special case that leaks 260kb per closed remote
connection. When we assume that a typical virsh user uses a single
connection per virsh invocation then we can view this as a static
leak.

Therefore, I'd say we could just leave this as-is for 0.9.4, except
Dan would be back soon and the problem is easy to fix for him.

Another problem is the libvirtd crash that Wen discovered. That's more
serious, as a misbehaving client shouldn't be able to crash libvirtd.

https://www.redhat.com/archives/libvir-list/2011-August/msg00005.html

-- 
Matthias Bolte
http://photron.blogspot.com