[libvirt] [PATCH] xen: Avoid deadlock in xenUnifiedDomainGetXMLDesc

So this is one way I am able to get this issue resolved. It might not be ideal as maybe there is a slight chance of inconsistencies. But at least it does not lock up anymore. -Stefan --- From: Stefan Bader <stefan.bader(a)canonical.com&gt; Date: Mon, 24 Jun 2013 09:30:20 +0200 Subject: [PATCH] xen: Avoid deadlock in xenUnifiedDomainGetXMLDesc Commit 95e18efd added the use virDomainDefPtr to several Xen driver methods. That structure is obtained by calling xenGetDomainDefForDom() which will acquire the mutex to the priv pointer. Unfortunately (at least) xenUnifiedDomainGetXMLDesc already takes that mutex and now is locking up while calling into xenDomainUsedCpus(). xenDomainUsedCpus ... nb_vcpu = xenUnifiedDomainGetMaxVcpus(dom); return xenUnifiedDomainGetVcpusFlags(...) ... if (!(def = xenGetDomainDefForDom(dom))) return xenGetDomainDefForUUID(dom->conn, dom->uuid); ... ret = xenHypervisorLookupDomainByUUID(conn, uuid); ... xenUnifiedLock(priv); name = xenStoreDomainGetName(conn, id); xenUnifiedUnlock(priv); ... if ((ncpus = xenUnifiedDomainGetVcpus(dom, cpuinfo, nb_vcpu, ... if (!(def = xenGetDomainDefForDom(dom))) [again like above] The deadlock is observable when connecting to a Xen host using the old xm stack and trying to obtain domain XML data from any running guest (like "dumpxml 0"). This would be a minimal fix that tries to avoid the deadlock. I am not completely sure this is not allowing a small window for getting inconsistent data. Signed-off-by: Stefan Bader <stefan.bader(a)canonical.com&gt; --- src/xen/xen_driver.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/src/xen/xen_driver.c b/src/xen/xen_driver.c index 3efc27a..64cc305 100644 --- a/src/xen/xen_driver.c +++ b/src/xen/xen_driver.c @@ -189,6 +189,7 @@ xenDomainUsedCpus(virDomainPtr dom) unsigned char *cpumap = NULL; size_t cpumaplen; int nb = 0; + int nbNodeCpus; int n, m; virVcpuInfoPtr cpuinfo = NULL; virNodeInfo nodeinfo; @@ -198,8 +199,11 @@ xenDomainUsedCpus(virDomainPtr dom) return NULL; priv = dom->conn->privateData; + xenUnifiedLock(priv); + nbNodeCpus = priv->nbNodeCpus; + xenUnifiedUnlock(priv); - if (priv->nbNodeCpus <= 0) + if (nbNodeCpus <= 0) return NULL; nb_vcpu = xenUnifiedDomainGetMaxVcpus(dom); if (nb_vcpu <= 0) @@ -207,7 +211,7 @@ xenDomainUsedCpus(virDomainPtr dom) if (xenUnifiedNodeGetInfo(dom->conn, &nodeinfo) < 0) return NULL; - if (!(cpulist = virBitmapNew(priv->nbNodeCpus))) { + if (!(cpulist = virBitmapNew(nbNodeCpus))) { virReportOOMError(); goto done; } @@ -225,7 +229,7 @@ xenDomainUsedCpus(virDomainPtr dom) if ((ncpus = xenUnifiedDomainGetVcpus(dom, cpuinfo, nb_vcpu, cpumap, cpumaplen)) >= 0) { for (n = 0; n < ncpus; n++) { - for (m = 0; m < priv->nbNodeCpus; m++) { + for (m = 0; m < nbNodeCpus; m++) { bool used; ignore_value(virBitmapGetBit(cpulist, m, &used)); if ((!used) && @@ -233,7 +237,7 @@ xenDomainUsedCpus(virDomainPtr dom) ignore_value(virBitmapSetBit(cpulist, m)); nb++; /* if all CPU are used just return NULL */ - if (nb == priv->nbNodeCpus) + if (nb == nbNodeCpus) goto done; } @@ -1403,9 +1407,7 @@ xenUnifiedDomainGetXMLDesc(virDomainPtr dom, unsigned int flags) def = xenXMDomainGetXMLDesc(dom->conn, minidef); } else { char *cpus; - xenUnifiedLock(priv); cpus = xenDomainUsedCpus(dom); - xenUnifiedUnlock(priv); def = xenDaemonDomainGetXMLDesc(dom->conn, minidef, cpus); VIR_FREE(cpus); } -- 1.7.9.5