On Tue, Nov 03, 2009 at 02:50:02PM -0500, Daniel P. Berrange wrote:
> In preparation of the monitor I/O process becoming fully asynchronous,
> it is neccessary to ensure all access to internals of the qemuMonitorPtr
> object is protected by a mutex lock.
>
> * src/qemu/qemu_monitor.c, src/qemu/qemu_monitor.h: Add mutex for locking
> monitor.
> * src/qemu/qemu_driver.c: Add locking around all monitor commands
> ---
> src/qemu/qemu_driver.c | 299 +++++++++++++++++++++++++++++++++++------------
> src/qemu/qemu_monitor.c | 19 +++
> src/qemu/qemu_monitor.h | 3 +
> 3 files changed, 248 insertions(+), 73 deletions(-)
[..]
> +++ b/src/qemu/qemu_driver.c
> @@ -141,6 +141,22 @@ static void qemuDomainObjPrivateFree(void *data)
> }
>
>
> +static void qemuDomainObjEnterMonitor(virDomainObjPtr obj)
> +{
> + qemuDomainObjPrivatePtr priv = obj->privateData;
> +
> + qemuMonitorLock(priv->mon);
> +}
> +
> +
> +static void qemuDomainObjExitMonitor(virDomainObjPtr obj)
> +{
> + qemuDomainObjPrivatePtr priv = obj->privateData;
> +
> + qemuMonitorUnlock(priv->mon);
> +}
> +
so we're using pthread mutex here and basically there is no way this
could go wrong and there is no need to handle errors, okay
> static int qemuCgroupControllerActive(struct qemud_driver *driver,
> int controller)
> {
the patch is quite regular
> + qemuDomainObjEnterMonitor(vm);
> + if (qemuMonitorStopCPUs(priv->mon) < 0) {
> + qemuDomainObjExitMonitor(vm);
> goto cleanup;
> + }
> + qemuDomainObjExitMonitor(vm);
to some extend I wonder if we shouldn't kill all those blocks and
always use the more regular form
qemuDomainObjEnterMonitor(vm);
ret = qemuMonitorStopCPUs(priv->mon);
qemuDomainObjExitMonitor(vm);
if (ret < 0)
goto cleanup;
it's simpler, easier to read, we don't have to think about matching
of Enter and Exit, and the generated code probably will be identical
In a number of places the refactoring introduced the later way but
the former is still present in a number of place, closer to original
code but doesn't make the patch safer I'm afraid. The only inconvenience
is the declaration of the temporary variable ...
[...]
>
> +void qemuMonitorLock(qemuMonitorPtr mon)
> +{
> + virMutexLock(&mon->lock);
> +}
> +
> +void qemuMonitorUnlock(qemuMonitorPtr mon)
> +{
> + virMutexUnlock(&mon->lock);
> +}
okay no error possible ...
Okay, I didn't spot anything suspect in the locking patch. But as
usual the problems may be in parts we may have forgotten about. Also
sometime the patch shows only a fraction of the relevant code.
Best is to push and test, ACK !
Daniel
--
Daniel Veillard | libxml Gnome XML XSLT toolkit http://xmlsoft.org/
daniel@xxxxxxxxxxxx | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library http://libvirt.org/
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