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Fix potential events deadlock when unref'ing virConnectPtr
When the last reference to a virConnectPtr is released by libvirtd, it was possible for a deadlock to occur in the virDomainEventState functions. The virDomainEventStatePtr holds a reference on virConnectPtr for each registered callback. When removing a callback, the virUnrefConnect function is run. If this causes the last reference on the virConnectPtr to be released, then virReleaseConnect can be run, which in turns calls qemudClose. This function has a call to virDomainEventStateDeregisterConn which is intended to remove all callbacks associated with the virConnectPtr instance. This will try to grab a lock on virDomainEventState but this lock is already held. Deadlock ensues Thread 1 (Thread 0x7fcbb526a840 (LWP 23185)): Since each callback associated with a virConnectPtr holds a reference on virConnectPtr, it is impossible for the qemudClose method to be invoked while any callbacks are still registered. Thus the call to virDomainEventStateDeregisterConn must in fact be a no-op. Thus it is possible to just remove all trace of virDomainEventStateDeregisterConn and avoid the deadlock. * src/conf/domain_event.c, src/conf/domain_event.h, src/libvirt_private.syms: Delete virDomainEventStateDeregisterConn * src/libxl/libxl_driver.c, src/lxc/lxc_driver.c, src/qemu/qemu_driver.c, src/uml/uml_driver.c: Remove calls to virDomainEventStateDeregisterConn
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@ -248,45 +248,6 @@ virDomainEventCallbackListRemoveID(virConnectPtr conn,
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}
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/**
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* virDomainEventCallbackListRemoveConn:
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* @conn: pointer to the connection
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* @cbList: the list
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*
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* Internal function to remove all of a given connection's callback
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* from a virDomainEventCallbackListPtr
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*/
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static int
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virDomainEventCallbackListRemoveConn(virConnectPtr conn,
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virDomainEventCallbackListPtr cbList)
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{
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int old_count = cbList->count;
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int i;
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for (i = 0 ; i < cbList->count ; i++) {
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if (cbList->callbacks[i]->conn == conn) {
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virFreeCallback freecb = cbList->callbacks[i]->freecb;
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if (freecb)
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(*freecb)(cbList->callbacks[i]->opaque);
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virUnrefConnect(cbList->callbacks[i]->conn);
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VIR_FREE(cbList->callbacks[i]);
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if (i < (cbList->count - 1))
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memmove(cbList->callbacks + i,
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cbList->callbacks + i + 1,
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sizeof(*(cbList->callbacks)) *
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(cbList->count - (i + 1)));
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cbList->count--;
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i--;
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}
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}
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if (cbList->count < old_count &&
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VIR_REALLOC_N(cbList->callbacks, cbList->count) < 0) {
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; /* Failure to reduce memory allocation isn't fatal */
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}
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return 0;
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}
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static int
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virDomainEventCallbackListMarkDelete(virConnectPtr conn,
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virDomainEventCallbackListPtr cbList,
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@ -1607,28 +1568,6 @@ virDomainEventStateDeregisterID(virConnectPtr conn,
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}
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/**
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* virDomainEventStateDeregisterConn:
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* @conn: connection to associate with callbacks
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* @state: domain event state
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*
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* Remove all callbacks from @state associated with the
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* connection @conn
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*
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* Returns 0 on success, -1 on error
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*/
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int
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virDomainEventStateDeregisterConn(virConnectPtr conn,
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virDomainEventStatePtr state)
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{
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int ret;
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virDomainEventStateLock(state);
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ret = virDomainEventCallbackListRemoveConn(conn, state->callbacks);
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virDomainEventStateUnlock(state);
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return ret;
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}
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/**
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* virDomainEventStateEventID:
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* @conn: connection associated with the callback
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@ -161,10 +161,6 @@ virDomainEventStateDeregisterID(virConnectPtr conn,
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int callbackID)
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ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2);
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int
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virDomainEventStateDeregisterConn(virConnectPtr conn,
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virDomainEventStatePtr state)
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ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2);
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int
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virDomainEventStateEventID(virConnectPtr conn,
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virDomainEventStatePtr state,
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int callbackID)
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@ -522,7 +522,6 @@ virDomainEventRebootNewFromDom;
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virDomainEventRebootNewFromObj;
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virDomainEventStateDeregister;
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virDomainEventStateDeregisterID;
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virDomainEventStateDeregisterConn;
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virDomainEventStateEventID;
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virDomainEventStateRegister;
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virDomainEventStateRegisterID;
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@ -1081,10 +1081,6 @@ libxlClose(virConnectPtr conn ATTRIBUTE_UNUSED)
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{
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libxlDriverPrivatePtr driver = conn->privateData;
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libxlDriverLock(driver);
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virDomainEventStateDeregisterConn(conn,
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driver->domainEventState);
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libxlDriverUnlock(driver);
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conn->privateData = NULL;
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return 0;
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}
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@ -178,8 +178,6 @@ static int lxcClose(virConnectPtr conn)
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lxc_driver_t *driver = conn->privateData;
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lxcDriverLock(driver);
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virDomainEventStateDeregisterConn(conn,
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driver->domainEventState);
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lxcProcessAutoDestroyRun(driver, conn);
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lxcDriverUnlock(driver);
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@ -962,8 +962,6 @@ static int qemudClose(virConnectPtr conn) {
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/* Get rid of callbacks registered for this conn */
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qemuDriverLock(driver);
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virDomainEventStateDeregisterConn(conn,
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driver->domainEventState);
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qemuDriverCloseCallbackRunAll(driver, conn);
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qemuDriverUnlock(driver);
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@ -1188,8 +1188,6 @@ static int umlClose(virConnectPtr conn) {
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struct uml_driver *driver = conn->privateData;
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umlDriverLock(driver);
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virDomainEventStateDeregisterConn(conn,
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driver->domainEventState);
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umlProcessAutoDestroyRun(driver, conn);
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umlDriverUnlock(driver);
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