Re: [libvirt] [PATCH v2] qemu_migration: Avoid crashing if domain dies too quickly

18 Oct 2013


      On 18.10.2013 06:06, Wangyufei (A) wrote:
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Thanks at first, this patch some kinda solve my problem until now. But I still have a doubt about this patch.
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-----Original Message-----
From: libvir-list-bounces@redhat.com
[mailto:libvir-list-bounces@redhat.com] On Behalf Of Michal Privoznik
Sent: Friday, October 11, 2013 8:15 PM
To: libvir-list@redhat.com
Subject: [libvirt] [PATCH v2] qemu_migration: Avoid crashing if domain dies
too quickly
...
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@@ -2673,6 +2677,8 @@ cleanup:
     virCommandFree(cmd);
     VIR_FREE(monarg);
     VIR_FREE(monpath);
+    virObjectUnref(vm);
Is this virObjectUnref(vm) corresponding to mon->vm = virObjectRef(vm) added in qemuMonitorOpenInternal?
If it is, how can we confirm virObjectRef(vm) has been done in qemuMonitorOpenInternal? If an error (anyone follows)happened in qemuMonitorOpenInternal is before mon->vm = virObjectRef(vm),
then we still goto cleanup and do virObjectUnref(vm), the refs will be wrong. Am I right?
Unfortunately, you've cut off the chunk above that allocates @mon.
Anyway, on initialization, @mon is filled with zeros. So until somebody
sets mon->vm [1] mon->vm is effectively NULL. And virObjectUnref() acts
like NOP on NULL.
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if (!cb->eofNotify) {
        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                       _("EOF notify callback must be supplied"));
        return NULL;
    }
    if (!cb->errorNotify) {
        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                       _("Error notify callback must be supplied"));
        return NULL;
    }
if (qemuMonitorInitialize() < 0)
        return NULL;
if (!(mon = virObjectLockableNew(qemuMonitorClass)))
        return NULL;
mon->fd = -1;
    mon->logfd = -1;
    if (virCondInit(&mon->notify) < 0) {
        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                       _("cannot initialize monitor condition"));
        goto cleanup;
    }
    mon->fd = fd;
    mon->hasSendFD = hasSendFD;
    mon->vm = virObjectRef(vm);
1: ^^ until after this line
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+    virObjectUnref(xmlopt);
if (pid != 0) {
         char ebuf[1024];
I hope it makes things a bit clearer.

Michal

    