Re: [PATCH] Avoid invoking the qemu monitor destroy callback if the constructor fails

[Jiri Denemark <jdenemar@xxxxxxxxxx>]

> diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
> index f428665..ff613a0 100644
> --- a/src/qemu/qemu_monitor.c
> +++ b/src/qemu/qemu_monitor.c
> @@ -671,6 +671,12 @@ qemuMonitorOpen(virDomainObjPtr vm,
>      return mon;
>  
>  cleanup:
> +    /* We don't want the 'destroy' callback invoked during
> +     * cleanup from construction failure, because that can
> +     * give a double-unref on virDomainObjPtr in the caller,
> +     * so kill the callbacks now.
> +     */
> +    mon->cb = NULL;
>      qemuMonitorUnlock(mon);
>      qemuMonitorClose(mon);
>      return NULL;

Unfortunately, this patch causes segfaults since qemuMonitorFree is not ready
to see mon->cb == NULL. On the other hand, we are lucky that this patch didn't
make it into the repository yet, so we can squash the following patch into it
before pushing:

diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
index f428665..9b050a0 100644
--- a/src/qemu/qemu_monitor.c
+++ b/src/qemu/qemu_monitor.c
@@ -198,7 +198,7 @@ void qemuMonitorUnlock(qemuMonitorPtr mon)
 static void qemuMonitorFree(qemuMonitorPtr mon)
 {
     VIR_DEBUG("mon=%p", mon);
-    if (mon->cb->destroy)
+    if (mon->cb && mon->cb->destroy)
         (mon->cb->destroy)(mon, mon->vm);
     if (virCondDestroy(&mon->notify) < 0)
     {}

Jirka

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