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

On 10/28/2013 01:06 PM, Daniel P. Berrange wrote: > On Mon, Oct 28, 2013 at 01:03:49PM -0400, Cole Robinson wrote: >> 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

Sorry for not being clear: The daemon crashes, that's the backtrace.