[libvirt] [PATCH v2 1/3] daemon: keep daemon until all hypervisors drivers are cleaned up

[Nikolay Shirokovskiy]

This fix SEGV with the backtrace [1]

This happens due to race on simultaneous finishing of libvirtd and
qemu process. We need to keep daemon object until all hypervisor
drivers are cleaned up. The other option is to take reference to
daemon in every hypervisor driver but this will take more work
and we really don't need to. Drivers cleanup procedure is synchronous
thus let's just remove last reference to daemon after drivers cleanup.

[1] backtrace (shortened a bit)

1  0x00007fd3a791b2e6 in virCondWait (c=<optimized out>, m=<optimized out>) at util/virthread.c:154
2  0x00007fd3a791bcb0 in virThreadPoolFree (pool=0x7fd38024ee00) at util/virthreadpool.c:266
3  0x00007fd38edaa00e in qemuStateCleanup () at qemu/qemu_driver.c:1116
4  0x00007fd3a79abfeb in virStateCleanup () at libvirt.c:808
5  0x00007fd3a85f2c9e in main (argc=<optimized out>, argv=<optimized out>) at libvirtd.c:1660

Thread 1 (Thread 0x7fd38722d700 (LWP 32256)):
0  0x00007fd3a7900910 in virClassIsDerivedFrom (klass=0xdfd36058d4853, parent=0x7fd3a8f394d0) at util/virobject.c:169
1  0x00007fd3a7900c4e in virObjectIsClass (anyobj=anyobj at entry=0x7fd3a8f2f850, klass=<optimized out>) at util/virobject.c:365
2  0x00007fd3a7900c74 in virObjectLock (anyobj=0x7fd3a8f2f850) at util/virobject.c:317
3  0x00007fd3a7a24d5d in virNetDaemonRemoveShutdownInhibition (dmn=0x7fd3a8f2f850) at rpc/virnetdaemon.c:547
4  0x00007fd38ed722cf in qemuProcessStop (driver=driver at entry=0x7fd380103810, vm=vm at entry=0x7fd38025b6d0, reason=reason at entry=VIR_DOMAIN_SHUTOFF_SHUTDOWN, asyncJob=asyncJob at entry=QEMU_ASYNC_JOB_NONE,
    flags=flags at entry=0) at qemu/qemu_process.c:5786
5  0x00007fd38edd9428 in processMonitorEOFEvent (vm=0x7fd38025b6d0, driver=0x7fd380103810) at qemu/qemu_driver.c:4588
6  qemuProcessEventHandler (data=<optimized out>, opaque=0x7fd380103810) at qemu/qemu_driver.c:4632
7  0x00007fd3a791bb55 in virThreadPoolWorker (opaque=opaque at entry=0x7fd3a8f1e4c0) at util/virthreadpool.c:145
---
 daemon/libvirtd.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/daemon/libvirtd.c b/daemon/libvirtd.c
index 95c1b1c..eefdefc 100644
--- a/daemon/libvirtd.c
+++ b/daemon/libvirtd.c
@@ -1628,7 +1628,6 @@ int main(int argc, char **argv) {
     virObjectUnref(qemuProgram);
     virObjectUnref(adminProgram);
     virNetDaemonClose(dmn);
-    virObjectUnref(dmn);
     virObjectUnref(srv);
     virObjectUnref(srvAdm);
     virNetlinkShutdown();
@@ -1658,6 +1657,9 @@ int main(int argc, char **argv) {
         driversInitialized = false;
         virStateCleanup();
     }
+    /* unref daemon only here as hypervisor drivers can
+       call shutdown inhibition functions on cleanup */
+    virObjectUnref(dmn);
 
     return ret;
 }
-- 
1.8.3.1