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>

diff --git a/src/conf/nwfilter_conf.c b/src/conf/nwfilter_conf.c
index 6db8ea9fbfe58933bd30921a7f235c7e29389425..52e1c062317623ed79612a13cfd64175359837f0 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);
 }
 
 
@@ -2990,14 +2995,12 @@ 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;
         }
 
@@ -3005,7 +3008,6 @@ virNWFilterObjAssignDef(virNWFilterObjListPtr nwfilters,
         /* trigger the update on VMs referencing the filter */
         if (virNWFilterTriggerVMFilterRebuild()) {
             nwfilter->newDef = NULL;
-            virNWFilterUnlockFilterUpdates();
             virNWFilterObjUnlock(nwfilter);
             return NULL;
         }
@@ -3013,12 +3015,9 @@ virNWFilterObjAssignDef(virNWFilterObjListPtr nwfilters,
         virNWFilterDefFree(nwfilter->def);
         nwfilter->def = def;
         nwfilter->newDef = NULL;
-        virNWFilterUnlockFilterUpdates();
         return nwfilter;
     }
 
-    virNWFilterUnlockFilterUpdates();
-
     if (VIR_ALLOC(nwfilter) < 0)
         return NULL;
 
@@ -3483,7 +3482,7 @@ int virNWFilterConfLayerInit(virDomainObjListIterator domUpdateCB,
 
     initialized = true;
 
-    if (virMutexInitRecursive(&updateMutex) < 0)
+    if (virRWLockInit(&updateLock) < 0)
         return -1;
 
     return 0;
@@ -3495,7 +3494,7 @@ 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 6b8b515500a49a75959df6532dc265921e7a2337..0d09b6a7d338924c61c778d832e6e7b0309ee734 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 94901c7ef02ef17808f79938aaf3fc24cdc6fc8c..1a8d08852fb877116db36d1378d47e0a4049abfc 100644 (file)
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -575,7 +575,6 @@ virNWFilterDefParseString;
 virNWFilterInstFiltersOnAllVMs;
 virNWFilterJumpTargetTypeToString;
 virNWFilterLoadAllConfigs;
-virNWFilterLockFilterUpdates;
 virNWFilterObjAssignDef;
 virNWFilterObjDeleteDef;
 virNWFilterObjFindByName;
@@ -587,6 +586,7 @@ virNWFilterObjSaveDef;
 virNWFilterObjUnlock;
 virNWFilterPrintStateMatchFlags;
 virNWFilterPrintTCPFlags;
+virNWFilterReadLockFilterUpdates;
 virNWFilterRegisterCallbackDriver;
 virNWFilterRuleActionTypeToString;
 virNWFilterRuleDirectionTypeToString;
@@ -594,6 +594,7 @@ virNWFilterRuleProtocolTypeToString;
 virNWFilterTestUnassignDef;
 virNWFilterUnlockFilterUpdates;
 virNWFilterUnRegisterCallbackDriver;
+virNWFilterWriteLockFilterUpdates;
 
 
 # conf/nwfilter_ipaddrmap.h

diff --git a/src/lxc/lxc_driver.c b/src/lxc/lxc_driver.c
index 982f3fc8c6ca062bf7506e4b06967609aed8d516..73a2986710e03f0abe4d8e5a6832052420259b51 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)
         virObjectEventStateQueue(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:
         virObjectEventStateQueue(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 d21dd82ac5b6e03f79a9c5dfb9e8bc2671f9fc85..5908df723c4c5e44d70e899623ac5c4d9068f0db 100644 (file)
--- a/src/nwfilter/nwfilter_driver.c
+++ b/src/nwfilter/nwfilter_driver.c
@@ -283,12 +283,14 @@ nwfilterStateReload(void)
     virNWFilterLearnThreadsTerminate(true);
 
     nwfilterDriverLock(driverState);
+    virNWFilterWriteLockFilterUpdates();
     virNWFilterCallbackDriversLock();
 
     virNWFilterLoadAllConfigs(&driverState->nwfilters,
                               driverState->configDir);
 
     virNWFilterCallbackDriversUnlock();
+    virNWFilterUnlockFilterUpdates();
     nwfilterDriverUnlock(driverState);
 
     virNWFilterInstFiltersOnAllVMs();
@@ -554,6 +556,7 @@ nwfilterDefineXML(virConnectPtr conn,
     virNWFilterPtr ret = NULL;
 
     nwfilterDriverLock(driver);
+    virNWFilterWriteLockFilterUpdates();
     virNWFilterCallbackDriversLock();
 
     if (!(def = virNWFilterDefParseString(xml)))
@@ -580,6 +583,7 @@ cleanup:
         virNWFilterObjUnlock(nwfilter);
 
     virNWFilterCallbackDriversUnlock();
+    virNWFilterUnlockFilterUpdates();
     nwfilterDriverUnlock(driver);
     return ret;
 }
@@ -592,10 +596,9 @@ nwfilterUndefine(virNWFilterPtr obj) {
     int ret = -1;
 
     nwfilterDriverLock(driver);
+    virNWFilterWriteLockFilterUpdates();
     virNWFilterCallbackDriversLock();
 
-    virNWFilterLockFilterUpdates();
-
     nwfilter = virNWFilterObjFindByUUID(&driver->nwfilters, obj->uuid);
     if (!nwfilter) {
         virReportError(VIR_ERR_NO_NWFILTER,
@@ -626,9 +629,8 @@ 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 89913cf8488305f96cb5b56aa7e6cbf40da2f046..8c5cd57b613395556ebf085c830ed4e81c7e503f 100644 (file)
--- a/src/nwfilter/nwfilter_gentech_driver.c
+++ b/src/nwfilter/nwfilter_gentech_driver.c
@@ -935,8 +935,6 @@ _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 */
@@ -964,8 +962,6 @@ _virNWFilterInstantiateFilter(virNWFilterDriverStatePtr driver,
                                         foundNewFilter);
 
 cleanup:
-    virNWFilterUnlockFilterUpdates();
-
     return rc;
 }
 
@@ -984,7 +980,7 @@ 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 6b3825aed06c32f58c211bc7ada5e0cc3e1b0133..0128356db5a922db72bbdca1a9f7a02087b912f7 100644 (file)
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -1576,6 +1576,8 @@ 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;
 
@@ -1656,6 +1658,7 @@ cleanup:
     }
     virObjectUnref(caps);
     virObjectUnref(qemuCaps);
+    virNWFilterUnlockFilterUpdates();
     return dom;
 }
 
@@ -6095,6 +6098,8 @@ qemuDomainCreateWithFlags(virDomainPtr dom, unsigned int flags)
                   VIR_DOMAIN_START_BYPASS_CACHE |
                   VIR_DOMAIN_START_FORCE_BOOT, -1);
 
+    virNWFilterReadLockFilterUpdates();
+
     if (!(vm = qemuDomObjFromDomain(dom)))
         return -1;
 
@@ -6122,6 +6127,7 @@ endjob:
 cleanup:
     if (vm)
         virObjectUnlock(vm);
+    virNWFilterUnlockFilterUpdates();
     return ret;
 }
 

diff --git a/src/uml/uml_driver.c b/src/uml/uml_driver.c
index 89afefef2e02f13e664ec2a856ab0bc802ed7434..309c10e95a621686c0f75ff5b9d617477bcd18e0 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;
 }