Re: [libvirt] [PATCH] Fix race condition reconnecting to vms & loading configs

On 10/28/2013 07:52 AM, Daniel P. Berrange wrote: > From: "Daniel P. Berrange" <berrange(a)redhat.com&gt; > > The following sequence > > 1. Define a persistent QMEU guest > 2. Start the QEMU guest > 3. Stop libvirtd > 4. Kill the QEMU process > 5. Start libvirtd > 6. List persistent guets > > At the last step, the previously running persistent guest > will be missing. This is because of a race condition in the > QEMU driver startup code. It does > > 1. Load all VM state files > 2. Spawn thread to reconnect to each VM > 3. Load all VM config files > > Only at the end of step 3, does the 'virDomainObjPtr' get > marked as "persistent". There is therefore a window where > the thread reconnecting to the VM will remove the persistent > VM from the list. > > The easy fix is to simply switch the order of steps 2 & 3. > > Signed-off-by: Daniel P. Berrange <berrange(a)redhat.com&gt; > --- > src/qemu/qemu_driver.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c > index c613967..9c3daad 100644 > --- a/src/qemu/qemu_driver.c > +++ b/src/qemu/qemu_driver.c > @@ -816,8 +816,6 @@ qemuStateInitialize(bool privileged, > > conn = virConnectOpen(cfg->uri); > > - qemuProcessReconnectAll(conn, qemu_driver); > - > /* Then inactive persistent configs */ > if (virDomainObjListLoadAllConfigs(qemu_driver->domains, > cfg->configDir, > @@ -828,6 +826,7 @@ qemuStateInitialize(bool privileged, > NULL, NULL) < 0) > goto error; > > + qemuProcessReconnectAll(conn, qemu_driver); > > virDomainObjListForEach(qemu_driver->domains, > qemuDomainSnapshotLoad, > I tried testing this patch to see if it would fix: https://bugzilla.redhat.com/show_bug.cgi?id=1015246 from current master I did: git revert a924d9d083c215df6044387057c501d9aa338b96 reproduce the bug git am <your-patch> But the daemon won't even start up after your patch is built: (gdb) bt #0 qemuMonitorOpen (vm=vm@entry=0x7fffd4211090, config=0x0, json=false, cb=cb@entry=0x7fffddcae720 <monitorCallbacks>, opaque=opaque@entry=0x7fffd419b840) at qemu/qemu_monitor.c:852 #1 0x00007fffdda1083d in qemuConnectMonitor ( driver=driver@entry=0x7fffd419b840, vm=vm@entry=0x7fffd4211090, logfd=logfd@entry=-1) at qemu/qemu_process.c:1412 #2 0x00007fffdda1685a in qemuProcessReconnect ( opaque=opaque@entry=0x7fffd422fef0) at qemu/qemu_process.c:3086 #3 0x00007ffff7528dce in virThreadHelper (data=<optimized out>) at util/virthreadpthread.c:161 #4 0x00007ffff4782f33 in start_thread (arg=0x7fffcb7fe700) at pthread_create.c:309 #5 0x00007ffff40a9ead in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111