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Re: [libvirt] [PATCH 3/3] hold an extra reference while handling watchdog event



On Wed, Mar 30, 2011 at 12:34:49PM +0800, Wen Congyang wrote:
> If the domain is not persistent, and qemu quited unexpectedly before
> calling processWatchdogEvent(), vm will be freed and the function
> processWatchdogEvent() will be dangerous.
> 
> ---
>  src/qemu/qemu_driver.c  |   10 ++++++----
>  src/qemu/qemu_process.c |    4 ++++
>  2 files changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index d79d61b..c9c681f 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -2443,15 +2443,17 @@ static void processWatchdogEvent(void *data, void *opaque)
>      }
>  
>  endjob:
> -    if (qemuDomainObjEndJob(wdEvent->vm) == 0)
> -        wdEvent->vm = NULL;
> +    /* Safe to ignore value since ref count was incremented in
> +     * qemuProcessHandleWatchdog().
> +     */
> +    ignore_value(qemuDomainObjEndJob(wdEvent->vm));
>  
>  unlock:
> -    if (wdEvent->vm)
> -        virDomainObjUnlock(wdEvent->vm);
>      qemuDriverUnlock(driver);
>  
>  cleanup:
> +    if (virDomainObjUnref(wdEvent->vm) > 0)
> +        virDomainObjUnlock(wdEvent->vm);

These two lines should be protected by qemu driver lock.

>      VIR_FREE(wdEvent);
>  }
>  
> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index e31e1b4..cd8c726 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -426,6 +426,10 @@ qemuProcessHandleWatchdog(qemuMonitorPtr mon ATTRIBUTE_UNUSED,
>          if (VIR_ALLOC(wdEvent) == 0) {
>              wdEvent->action = VIR_DOMAIN_WATCHDOG_ACTION_DUMP;
>              wdEvent->vm = vm;
> +            /* Hold an extra reference because we can't allow 'vm' to be
> +             * deleted before handling watchdog event is finished.
> +             */
> +            virDomainObjRef(vm);
>              ignore_value(virThreadPoolSendJob(driver->workerPool, wdEvent));
>          } else
>              virReportOOMError();
> -- 
> 1.7.1


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