Re: [libvirt] [PATCH] Release VM lock before acquiring virDomainObjListPtr lock
On Mon, Apr 08, 2013 at 09:15:28PM -0600, Eric Blake wrote:
On 02/11/2013 09:46 AM, Daniel P. Berrange wrote:
> From: "Daniel P. Berrange" <berrange(a)redhat.com>
>
> When removing a VM from the virDomainObjListPtr, we must not
> be holding the VM lock while acquiring the list lock. Re-order
> code to ensure that we can release the VM lock early.
> ---
> src/conf/domain_conf.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
> index 5e16ddf..d92e54a 100644
> --- a/src/conf/domain_conf.c
> +++ b/src/conf/domain_conf.c
> @@ -2115,11 +2115,10 @@ void virDomainObjListRemove(virDomainObjListPtr doms,
> {
> char uuidstr[VIR_UUID_STRING_BUFLEN];
>
> - virObjectLock(doms);
> virUUIDFormat(dom->def->uuid, uuidstr);
> -
> virObjectUnlock(dom);
>
> + virObjectLock(doms);
This patch seems to be implicated in Peter's latest proof of a
use-after-free data race:
https://www.redhat.com/archives/libvir-list/2013-April/msg00674.html
The caller of this method should own a reference on virDomainObjPtr.
This method will result in that reference being released, as the
dom is removed from the list.
If any other thread experiances a use-after-free, then that thread
must have been missing a reference.
I'm trying to understand what the behavior was before this patch
went in.
Well this was just fixing a deadlock introduced in a previous patch.
You need to look further back than just this patch. Originally the
global QEMU driver lock would be held preventing any kind of concurrent
execution.
Regards,
Daniel
--
|: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org -o- http://virt-manager.org :|
|: http://autobuild.org -o- http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|