On 03/27/2017 06:47 PM, John Ferlan wrote:
Based upon an idea and some research by Wang King <king.wang@huawei.com> and xinhua.Cao <caoxinhua@huawei.com>.
Since we're assigning the 'client' to our callback event lookaside list, it's imperative that we grab a reference to the object; otherwise, when the object is unref'd during virNetServerProcessClients when it's determined that the virNetServerClientIsClosed and the memory is free'd before perhaps the object event state callbacks are run. When a virObjectLock() is run, before sending the message the following trace occurs;
#0 0x00007fda223d66d8 in virClassIsDerivedFrom (klass=0xdeadbeef, parent=0x7fda24c81b40) at util/virobject.c:169 #1 0x00007fda223d6a1e in virObjectIsClass (anyobj=anyobj@entry=0x7fd9e575b400, klass=<optimized out>) at util/virobject.c:365 #2 0x00007fda223d6a44 in virObjectLock (anyobj=0x7fd9e575b400) at util/virobject.c:317 #3 0x00007fda22507f71 in virNetServerClientSendMessage (client=client@entry=0x7fd9e575b400, msg=msg@entry=0x7fd9ec30de90) at rpc/virnetserverclient.c:1422 #4 0x00007fda230d714d in remoteDispatchObjectEventSend (client=0x7fd9e575b400, program=0x7fda24c844e0, procnr=348, proc=0x7fda2310e5e0 <xdr_remote_domain_event_callback_tunable_msg>, data=0x7ffc3857fdb0) at remote.c:3803 #5 0x00007fda230dd71b in remoteRelayDomainEventTunable (conn=<optimized out>, dom=0x7fda27cd7660, params=0x7fda27f3aae0, nparams=1,opaque=0x7fd9e6c99e00) at remote.c:1033 #6 0x00007fda224484cb in virDomainEventDispatchDefaultFunc (conn=0x7fda27cd0120, event=0x7fda2736ea00, cb=0x7fda230dd610 <remoteRelayDomainEventTunable>, cbopaque=0x7fd9e6c99e00) at conf/domain_event.c:1910 #7 0x00007fda22446871 in virObjectEventStateDispatchCallbacks (callbacks=<optimized out>, callbacks=<optimized out>, event=0x7fda2736ea00,state=0x7fda24ca3960) at conf/object_event.c:722 #8 virObjectEventStateQueueDispatch (callbacks=0x7fda24c65800, queue=0x7ffc3857fe90, state=0x7fda24ca3960) at conf/object_event.c:736 #9 virObjectEventStateFlush (state=0x7fda24ca3960) at conf/object_event.c:814 #10 virObjectEventTimer (timer=<optimized out>, opaque=0x7fda24ca3960) at conf/object_event.c:560 #11 0x00007fda223ae8b9 in virEventPollDispatchTimeouts () at util/vireventpoll.c:458 #12 virEventPollRunOnce () at util/vireventpoll.c:654 #13 0x00007fda223ad1d2 in virEventRunDefaultImpl () at util/virevent.c:314 #14 0x00007fda225046cd in virNetDaemonRun (dmn=0x7fda24c775c0) at rpc/virnetdaemon.c:818 #15 0x00007fda230d6351 in main (argc=<optimized out>, argv=<optimized out>) at libvirtd.c:1623
Signed-off-by: John Ferlan <jferlan@redhat.com> --- daemon/remote.c | 38 +++++++++++++++++++++----------------- 1 file changed, 21 insertions(+), 17 deletions(-)
diff --git a/daemon/remote.c b/daemon/remote.c index 5cdc53e..25a29cf 100644 --- a/daemon/remote.c +++ b/daemon/remote.c @@ -124,7 +124,11 @@ remoteDispatchObjectEventSend(virNetServerClientPtr client, static void remoteEventCallbackFree(void *opaque) { - VIR_FREE(opaque); + daemonClientEventCallbackPtr callback = opaque; + if (!callback) + return; + virObjectUnref(callback->client); + VIR_FREE(callback); }
@@ -3896,7 +3900,7 @@ remoteDispatchConnectDomainEventRegister(virNetServerPtr server ATTRIBUTE_UNUSED */ if (VIR_ALLOC(callback) < 0) goto cleanup; - callback->client = client; + callback->client = virObjectRef(client); callback->eventID = VIR_DOMAIN_EVENT_ID_LIFECYCLE; callback->callbackID = -1; callback->legacy = true; @@ -3923,7 +3927,7 @@ remoteDispatchConnectDomainEventRegister(virNetServerPtr server ATTRIBUTE_UNUSED rv = 0;
cleanup: - VIR_FREE(callback); + remoteEventCallbackFree(callback); if (rv < 0) virNetMessageSaveError(rerr); virMutexUnlock(&priv->lock);
I don't really see how this could work in the first place. I mean, @callback is allocated in the chunk above. Cool. Then, in between these two chunks it's passed (under code name @ref) to virConnectDomainEventRegisterAny() ... Aaand I get it now. Just realized that VIR_APPEND_ELEMENT() sets @callback to NULL. So we are safe here. D'oh. ACK Michal