[libvirt] [PATCH 1/2] remote: Avoid the thread race condition

[Osier Yang]

From: Daniel P. Berrange <berrange at redhat.com>

https://bugzilla.redhat.com/show_bug.cgi?id=866524

Since the virConnect object is not locked wholely when doing
virConenctDispose, a thread can get the lock and thus might
cause the race.

Detected by valgrind:

==23687== Invalid read of size 4
==23687==    at 0x38BAA091EC: pthread_mutex_lock (pthread_mutex_lock.c:61)
==23687==    by 0x3FBA919E36: remoteClientCloseFunc (remote_driver.c:337)
==23687==    by 0x3FBA936BF2: virNetClientCloseLocked (virnetclient.c:688)
==23687==    by 0x3FBA9390D8: virNetClientIncomingEvent (virnetclient.c:1859)
==23687==    by 0x3FBA851AAE: virEventPollRunOnce (event_poll.c:485)
==23687==    by 0x3FBA850846: virEventRunDefaultImpl (event.c:247)
==23687==    by 0x40CD61: vshEventLoop (virsh.c:2128)
==23687==    by 0x3FBA8626F8: virThreadHelper (threads-pthread.c:161)
==23687==    by 0x38BAA077F0: start_thread (pthread_create.c:301)
==23687==    by 0x33F68E570C: clone (clone.S:115)
==23687==  Address 0x4ca94e0 is 144 bytes inside a block of size 312 free'd
==23687==    at 0x4A0595D: free (vg_replace_malloc.c:366)
==23687==    by 0x3FBA8588B8: virFree (memory.c:309)
==23687==    by 0x3FBA86AAFC: virObjectUnref (virobject.c:145)
==23687==    by 0x3FBA8EA767: virConnectClose (libvirt.c:1458)
==23687==    by 0x40C8B8: vshDeinit (virsh.c:2584)
==23687==    by 0x41071E: main (virsh.c:3022)

The above race is caused by the eventLoop thread tries to handle
the net client event by calling the callback set by:
    virNetClientSetCloseCallback(priv->client,
                                 remoteClientCloseFunc,
                                 conn, NULL);

I.E. remoteClientCloseFunc, which lock/unlock the virConnect object.

This patch is to fix the bug by setting the callback to NULL when
doRemoteClose.
---
 src/remote/remote_driver.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/src/remote/remote_driver.c b/src/remote/remote_driver.c
index e5d4af3..5cc7e32 100644
--- a/src/remote/remote_driver.c
+++ b/src/remote/remote_driver.c
@@ -1003,6 +1003,10 @@ doRemoteClose(virConnectPtr conn, struct private_data *priv)
 
     virObjectUnref(priv->tls);
     priv->tls = NULL;
+    virNetClientSetCloseCallback(priv->client,
+                                 NULL,
+                                 NULL,
+                                 NULL);
     virNetClientClose(priv->client);
     virObjectUnref(priv->client);
     priv->client = NULL;
-- 
1.7.7.6