Push nwfilter update locking up to top level

The NWFilter code has as a deadlock race condition between
the virNWFilter{Define,Undefine} APIs and starting of guest
VMs due to mis-matched lock ordering.

In the virNWFilter{Define,Undefine} codepaths the lock ordering
is

  1. nwfilter driver lock
  2. virt driver lock
  3. nwfilter update lock
  4. domain object lock

In the VM guest startup paths the lock ordering is

  1. virt driver lock
  2. domain object lock
  3. nwfilter update lock

As can be seen the domain object and nwfilter update locks are
not acquired in a consistent order.

The fix used is to push the nwfilter update lock upto the top
level resulting in a lock ordering for virNWFilter{Define,Undefine}
of

  1. nwfilter driver lock
  2. nwfilter update lock
  3. virt driver lock
  4. domain object lock

and VM start using

  1. nwfilter update lock
  2. virt driver lock
  3. domain object lock

This has the effect of serializing VM startup once again, even if
no nwfilters are applied to the guest. There is also the possibility
of deadlock due to a call graph loop via virNWFilterInstantiate
and virNWFilterInstantiateFilterLate.

These two problems mean the lock must be turned into a read/write
lock instead of a plain mutex at the same time. The lock is used to
serialize changes to the "driver->nwfilters" hash, so the write lock
only needs to be held by the define/undefine methods. All other
methods can rely on a read lock which allows good concurrency.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
(cherry picked from commit 6e5c79a1b5a8b3a23e7df7ffe58fb272aa17fbfb)

diff --git a/src/conf/nwfilter_conf.c b/src/conf/nwfilter_conf.c
index 7152aae3dd1dc6da8556c2166d385328c425d4d6..6b71e1788df2925aebeccb17ffcb1ca9796f34ac 100644 (file)
--- a/src/conf/nwfilter_conf.c
+++ b/src/conf/nwfilter_conf.c
@@ -143,17 +143,22 @@ static const struct int_map chain_priorities[] = {
 /*
  * only one filter update allowed
  */
-static virMutex updateMutex;
+static virRWLock updateLock;
 static bool initialized = false;
 
 void
-virNWFilterLockFilterUpdates(void) {
-    virMutexLock(&updateMutex);
+virNWFilterReadLockFilterUpdates(void) {
+    virRWLockRead(&updateLock);
+}
+
+void
+virNWFilterWriteLockFilterUpdates(void) {
+    virRWLockWrite(&updateLock);
 }
 
 void
 virNWFilterUnlockFilterUpdates(void) {
-    virMutexUnlock(&updateMutex);
+    virRWLockUnlock(&updateLock);
 }
 
 
@@ -2982,14 +2987,12 @@ virNWFilterObjAssignDef(virNWFilterObjListPtr nwfilters,
         return NULL;
     }
 
-    virNWFilterLockFilterUpdates();
 
     if ((nwfilter = virNWFilterObjFindByName(nwfilters, def->name))) {
 
         if (virNWFilterDefEqual(def, nwfilter->def, false)) {
             virNWFilterDefFree(nwfilter->def);
             nwfilter->def = def;
-            virNWFilterUnlockFilterUpdates();
             return nwfilter;
         }
 
@@ -2997,7 +3000,6 @@ virNWFilterObjAssignDef(virNWFilterObjListPtr nwfilters,
         /* trigger the update on VMs referencing the filter */
         if (virNWFilterTriggerVMFilterRebuild()) {
             nwfilter->newDef = NULL;
-            virNWFilterUnlockFilterUpdates();
             virNWFilterObjUnlock(nwfilter);
             return NULL;
         }
@@ -3005,12 +3007,9 @@ virNWFilterObjAssignDef(virNWFilterObjListPtr nwfilters,
         virNWFilterDefFree(nwfilter->def);
         nwfilter->def = def;
         nwfilter->newDef = NULL;
-        virNWFilterUnlockFilterUpdates();
         return nwfilter;
     }
 
-    virNWFilterUnlockFilterUpdates();
-
     if (VIR_ALLOC(nwfilter) < 0)
         return NULL;
 
@@ -3475,7 +3474,7 @@ int virNWFilterConfLayerInit(virDomainObjListIterator domUpdateCB,
 
     initialized = true;
 
-    if (virMutexInitRecursive(&updateMutex) < 0)
+    if (virRWLockInit(&updateLock) < 0)
         return -1;
 
     return 0;
@@ -3487,7 +3486,7 @@ void virNWFilterConfLayerShutdown(void)
     if (!initialized)
         return;
 
-    virMutexDestroy(&updateMutex);
+    virRWLockDestroy(&updateLock);
 
     initialized = false;
     virNWFilterDomainFWUpdateOpaque = NULL;

diff --git a/src/conf/nwfilter_conf.h b/src/conf/nwfilter_conf.h
index 29906f1389c6920515a2a2ef7732e093943f5e02..d460a0856531c628a49560eae700298ab2d6c34a 100644 (file)
--- a/src/conf/nwfilter_conf.h
+++ b/src/conf/nwfilter_conf.h
@@ -716,7 +716,8 @@ virNWFilterDefPtr virNWFilterDefParseFile(const char *filename);
 void virNWFilterObjLock(virNWFilterObjPtr obj);
 void virNWFilterObjUnlock(virNWFilterObjPtr obj);
 
-void virNWFilterLockFilterUpdates(void);
+void virNWFilterWriteLockFilterUpdates(void);
+void virNWFilterReadLockFilterUpdates(void);
 void virNWFilterUnlockFilterUpdates(void);
 
 int virNWFilterConfLayerInit(virDomainObjListIterator domUpdateCB, void *opaque);

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 982907bd97c997d7acb3a433e450bdc178fe5b57..291b32835901c77e6d72b5f2e4e19e6940e44f09 100644 (file)
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -569,7 +569,6 @@ virNWFilterDefParseString;
 virNWFilterInstFiltersOnAllVMs;
 virNWFilterJumpTargetTypeToString;
 virNWFilterLoadAllConfigs;
-virNWFilterLockFilterUpdates;
 virNWFilterObjAssignDef;
 virNWFilterObjDeleteDef;
 virNWFilterObjFindByName;
@@ -581,6 +580,7 @@ virNWFilterObjSaveDef;
 virNWFilterObjUnlock;
 virNWFilterPrintStateMatchFlags;
 virNWFilterPrintTCPFlags;
+virNWFilterReadLockFilterUpdates;
 virNWFilterRegisterCallbackDriver;
 virNWFilterRuleActionTypeToString;
 virNWFilterRuleDirectionTypeToString;
@@ -588,6 +588,7 @@ virNWFilterRuleProtocolTypeToString;
 virNWFilterTestUnassignDef;
 virNWFilterUnlockFilterUpdates;
 virNWFilterUnRegisterCallbackDriver;
+virNWFilterWriteLockFilterUpdates;
 
 
 # conf/nwfilter_ipaddrmap.h

diff --git a/src/lxc/lxc_driver.c b/src/lxc/lxc_driver.c
index 94b4668c7b08dc625a98d315beebff7d09654d1d..56673ec2d85cf08336713af65afb6c6f5b1bba2a 100644 (file)
--- a/src/lxc/lxc_driver.c
+++ b/src/lxc/lxc_driver.c
@@ -1015,6 +1015,8 @@ static int lxcDomainCreateWithFiles(virDomainPtr dom,
 
     virCheckFlags(VIR_DOMAIN_START_AUTODESTROY, -1);
 
+    virNWFilterReadLockFilterUpdates();
+
     if (!(vm = lxcDomObjFromDomain(dom)))
         goto cleanup;
 
@@ -1053,6 +1055,7 @@ cleanup:
     if (event)
         virDomainEventStateQueue(driver->domainEventState, event);
     virObjectUnref(cfg);
+    virNWFilterUnlockFilterUpdates();
     return ret;
 }
 
@@ -1109,6 +1112,8 @@ lxcDomainCreateXMLWithFiles(virConnectPtr conn,
 
     virCheckFlags(VIR_DOMAIN_START_AUTODESTROY, NULL);
 
+    virNWFilterReadLockFilterUpdates();
+
     if (!(caps = virLXCDriverGetCapabilities(driver, false)))
         goto cleanup;
 
@@ -1164,6 +1169,7 @@ cleanup:
         virDomainEventStateQueue(driver->domainEventState, event);
     virObjectUnref(caps);
     virObjectUnref(cfg);
+    virNWFilterUnlockFilterUpdates();
     return dom;
 }
 

diff --git a/src/nwfilter/nwfilter_driver.c b/src/nwfilter/nwfilter_driver.c
index 0a4d60546895f8992aee2b8162a20b005669ab82..df3a143885060250da0b95d260989f38b95c7c1f 100644 (file)
--- a/src/nwfilter/nwfilter_driver.c
+++ b/src/nwfilter/nwfilter_driver.c
@@ -284,12 +284,14 @@ nwfilterStateReload(void)
     virNWFilterLearnThreadsTerminate(true);
 
     nwfilterDriverLock(driverState);
+    virNWFilterWriteLockFilterUpdates();
     virNWFilterCallbackDriversLock();
 
     virNWFilterLoadAllConfigs(&driverState->nwfilters,
                               driverState->configDir);
 
     virNWFilterCallbackDriversUnlock();
+    virNWFilterUnlockFilterUpdates();
     nwfilterDriverUnlock(driverState);
 
     virNWFilterInstFiltersOnAllVMs();
@@ -555,6 +557,7 @@ nwfilterDefineXML(virConnectPtr conn,
     virNWFilterPtr ret = NULL;
 
     nwfilterDriverLock(driver);
+    virNWFilterWriteLockFilterUpdates();
     virNWFilterCallbackDriversLock();
 
     if (!(def = virNWFilterDefParseString(xml)))
@@ -581,6 +584,7 @@ cleanup:
         virNWFilterObjUnlock(nwfilter);
 
     virNWFilterCallbackDriversUnlock();
+    virNWFilterUnlockFilterUpdates();
     nwfilterDriverUnlock(driver);
     return ret;
 }
@@ -593,10 +597,9 @@ nwfilterUndefine(virNWFilterPtr obj) {
     int ret = -1;
 
     nwfilterDriverLock(driver);
+    virNWFilterWriteLockFilterUpdates();
     virNWFilterCallbackDriversLock();
 
-    virNWFilterLockFilterUpdates();
-
     nwfilter = virNWFilterObjFindByUUID(&driver->nwfilters, obj->uuid);
     if (!nwfilter) {
         virReportError(VIR_ERR_NO_NWFILTER,
@@ -627,9 +630,8 @@ cleanup:
     if (nwfilter)
         virNWFilterObjUnlock(nwfilter);
 
-    virNWFilterUnlockFilterUpdates();
-
     virNWFilterCallbackDriversUnlock();
+    virNWFilterUnlockFilterUpdates();
     nwfilterDriverUnlock(driver);
     return ret;
 }

diff --git a/src/nwfilter/nwfilter_gentech_driver.c b/src/nwfilter/nwfilter_gentech_driver.c
index 59611655e749e387efd08fb8603446e199549584..42c3dd70d8e512c286d5ce5c5c94b9d8b9eb7f97 100644 (file)
--- a/src/nwfilter/nwfilter_gentech_driver.c
+++ b/src/nwfilter/nwfilter_gentech_driver.c
@@ -934,8 +934,6 @@ _virNWFilterInstantiateFilter(virNWFilterDriverStatePtr driver,
     int ifindex;
     int rc;
 
-    virNWFilterLockFilterUpdates();
-
     /* after grabbing the filter update lock check for the interface; if
        it's not there anymore its filters will be or are being removed
        (while holding the lock) and we don't want to build new ones */
@@ -963,8 +961,6 @@ _virNWFilterInstantiateFilter(virNWFilterDriverStatePtr driver,
                                         foundNewFilter);
 
 cleanup:
-    virNWFilterUnlockFilterUpdates();
-
     return rc;
 }
 
@@ -983,7 +979,7 @@ virNWFilterInstantiateFilterLate(virNWFilterDriverStatePtr driver,
     int rc;
     bool foundNewFilter = false;
 
-    virNWFilterLockFilterUpdates();
+    virNWFilterReadLockFilterUpdates();
 
     rc = __virNWFilterInstantiateFilter(driver,
                                         vmuuid,

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 9666d3923d0bf5ea51add8fceaec729638423d63..67fe06f69c15b25c09b0bdd30c738fbdfdfd3679 100644 (file)
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -1577,6 +1577,8 @@ static virDomainPtr qemuDomainCreateXML(virConnectPtr conn,
     if (flags & VIR_DOMAIN_START_AUTODESTROY)
         start_flags |= VIR_QEMU_PROCESS_START_AUTODESTROY;
 
+    virNWFilterReadLockFilterUpdates();
+
     if (!(caps = virQEMUDriverGetCapabilities(driver, false)))
         goto cleanup;
 
@@ -1657,6 +1659,7 @@ cleanup:
     }
     virObjectUnref(caps);
     virObjectUnref(qemuCaps);
+    virNWFilterUnlockFilterUpdates();
     return dom;
 }
 
@@ -6066,6 +6069,8 @@ qemuDomainCreateWithFlags(virDomainPtr dom, unsigned int flags)
                   VIR_DOMAIN_START_BYPASS_CACHE |
                   VIR_DOMAIN_START_FORCE_BOOT, -1);
 
+    virNWFilterReadLockFilterUpdates();
+
     if (!(vm = qemuDomObjFromDomain(dom)))
         return -1;
 
@@ -6093,6 +6098,7 @@ endjob:
 cleanup:
     if (vm)
         virObjectUnlock(vm);
+    virNWFilterUnlockFilterUpdates();
     return ret;
 }
 

diff --git a/src/uml/uml_driver.c b/src/uml/uml_driver.c
index cf7f334bd374a5885d7e8d5838e220d6ca284265..786061413101e0891025b88a06e5a9567ddebb14 100644 (file)
--- a/src/uml/uml_driver.c
+++ b/src/uml/uml_driver.c
@@ -1574,6 +1574,7 @@ static virDomainPtr umlDomainCreateXML(virConnectPtr conn, const char *xml,
 
     virCheckFlags(VIR_DOMAIN_START_AUTODESTROY, NULL);
 
+    virNWFilterReadLockFilterUpdates();
     umlDriverLock(driver);
     if (!(def = virDomainDefParseString(xml, driver->caps, driver->xmlopt,
                                         1 << VIR_DOMAIN_VIRT_UML,
@@ -1613,6 +1614,7 @@ cleanup:
     if (event)
         umlDomainEventQueue(driver, event);
     umlDriverUnlock(driver);
+    virNWFilterUnlockFilterUpdates();
     return dom;
 }
 
@@ -1997,6 +1999,7 @@ static int umlDomainCreateWithFlags(virDomainPtr dom, unsigned int flags) {
 
     virCheckFlags(VIR_DOMAIN_START_AUTODESTROY, -1);
 
+    virNWFilterReadLockFilterUpdates();
     umlDriverLock(driver);
     vm = virDomainObjListFindByUUID(driver->domains, dom->uuid);
 
@@ -2023,6 +2026,7 @@ cleanup:
     if (event)
         umlDomainEventQueue(driver, event);
     umlDriverUnlock(driver);
+    virNWFilterUnlockFilterUpdates();
     return ret;
 }