commit 33c6eb9689eb51dfe31dd05b24b3b6b1c948c267
Author: Jim Fehlig <jfehlig@suse.com>
Date:   Thu Mar 8 15:04:48 2018 -0700

    libvirtd: fix potential deadlock when reloading
    
    It is possible to deadlock libvirtd when concurrently starting a domain
    and restarting the daemon. Threads involved in the deadlock are
    
    Thread 4 (Thread 0x7fc13b53e700 (LWP 64084)):
    /lib64/libpthread.so.0
        at util/virthread.c:154
        at qemu/qemu_monitor.c:1083
        cmd=0x7fc110017700, scm_fd=-1, reply=0x7fc13b53d318) at
    qemu/qemu_monitor_json.c:305
    cmd=0x7fc110017700,
        reply=0x7fc13b53d318) at qemu/qemu_monitor_json.c:335
        at qemu/qemu_monitor_json.c:1298
        at qemu/qemu_monitor.c:1697
        vm=0x7fc110003d00, asyncJob=QEMU_ASYNC_JOB_START) at qemu/qemu_process.c:1763
    vm=0x7fc110003d00,
        asyncJob=6, logCtxt=0x7fc1100089c0) at qemu/qemu_process.c:1835
        vm=0x7fc110003d00, asyncJob=6, logCtxt=0x7fc1100089c0) at
    qemu/qemu_process.c:2180
    driver=0x7fc12004e1e0,
        vm=0x7fc110003d00, asyncJob=QEMU_ASYNC_JOB_START, incoming=0x0, snapshot=0x0,
        vmop=VIR_NETDEV_VPORT_PROFILE_OP_CREATE, flags=17) at qemu/qemu_process.c:6111
    driver=0x7fc12004e1e0,
        vm=0x7fc110003d00, updatedCPU=0x0, asyncJob=QEMU_ASYNC_JOB_START,
    migrateFrom=0x0,
        migrateFd=-1, migratePath=0x0, snapshot=0x0,
    vmop=VIR_NETDEV_VPORT_PROFILE_OP_CREATE,
        flags=17) at qemu/qemu_process.c:6334
        xml=0x7fc110000ed0 "<!--\nWARNING: THIS IS AN AUTO-GENERATED FILE.
    CHANGES TO IT ARE LIKELY TO BE\nOVERWRITTEN AND LOST. Changes to this xml
    configuration should be made using:\n  virsh edit testvv\nor other
    applicati"..., flags=0) at qemu/qemu_driver.c:1776
    ...
    
    Thread 1 (Thread 0x7fc143c66880 (LWP 64081)):
    /lib64/libpthread.so.0
        at util/virthread.c:122
    conf/nwfilter_conf.c:159
    sig=0x7ffe0a831e30,
        opaque=0x0) at remote/remote_daemon.c:724
        opaque=0x558c5328b230) at rpc/virnetdaemon.c:654
        at util/vireventpoll.c:508
    rpc/virnetdaemon.c:858
    remote/remote_daemon.c:1496
    (gdb) thr 1
    [Switching to thread 1 (Thread 0x7fc143c66880 (LWP 64081))]
    /lib64/libpthread.so.0
    (gdb) f 1
        at util/virthread.c:122
    122         pthread_rwlock_wrlock(&m->lock);
    (gdb) p updateLock
    $1 = {lock = {__data = {__lock = 0, __nr_readers = 1, __readers_wakeup = 0,
          __writer_wakeup = 0, __nr_readers_queued = 0, __nr_writers_queued = 1,
    __writer = 0,
          __shared = 0, __rwelision = 0 '\000', __pad1 = "\000\000\000\000\000\000",
          __pad2 = 0, __flags = 0},
        __size = "\000\000\000\000\001", '\000' <repeats 15 times>, "\001",
    '\000' <repeats 34 times>, __align = 4294967296}}
    
    Reloading of the nwfilter driver is stuck waiting for a write lock, which
    already has a reader (from qemuDomainCreateXML) in the critical section.
    Since the reload occurs in the context of the main event loop thread,
    libvirtd becomes deadlocked. The deadlock can be avoided by offloading
    the reload work to a thread.
    
    Signed-off-by: Jim Fehlig <jfehlig@suse.com>
    Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

Index: libvirt-4.1.0/src/remote/remote_daemon.c
===================================================================
--- libvirt-4.1.0.orig/src/remote/remote_daemon.c
+++ libvirt-4.1.0/src/remote/remote_daemon.c
@@ -709,20 +709,32 @@ static void daemonShutdownHandler(virNet
     virNetDaemonQuit(dmn);
 }
 
+static void daemonReloadHandlerThread(void *opague ATTRIBUTE_UNUSED)
+{
+    VIR_INFO("Reloading configuration on SIGHUP");
+    virHookCall(VIR_HOOK_DRIVER_DAEMON, "-",
+                VIR_HOOK_DAEMON_OP_RELOAD, SIGHUP, "SIGHUP", NULL, NULL);
+    if (virStateReload() < 0)
+        VIR_WARN("Error while reloading drivers");
+}
+
 static void daemonReloadHandler(virNetDaemonPtr dmn ATTRIBUTE_UNUSED,
                                 siginfo_t *sig ATTRIBUTE_UNUSED,
                                 void *opaque ATTRIBUTE_UNUSED)
 {
+    virThread thr;
+
     if (!driversInitialized) {
         VIR_WARN("Drivers are not initialized, reload ignored");
         return;
     }
 
-    VIR_INFO("Reloading configuration on SIGHUP");
-    virHookCall(VIR_HOOK_DRIVER_DAEMON, "-",
-                VIR_HOOK_DAEMON_OP_RELOAD, SIGHUP, "SIGHUP", NULL, NULL);
-    if (virStateReload() < 0)
-        VIR_WARN("Error while reloading drivers");
+    if (virThreadCreate(&thr, false, daemonReloadHandlerThread, NULL) < 0) {
+        /*
+         * Not much we can do on error here except log it.
+         */
+        VIR_ERROR(_("Failed to create thread to handle daemon restart"));
+    }
 }
 
 static int daemonSetupSignals(virNetDaemonPtr dmn)