On Fri, Mar 02, 2018 at 03:24:53PM -0700, Jim Fehlig wrote: > On 03/02/2018 11:12 AM, Daniel P. Berrangé wrote: > > On Fri, Mar 02, 2018 at 04:52:23PM +0000, Daniel P. Berrangé wrote: > > > On Thu, Mar 01, 2018 at 04:42:36PM -0700, Jim Fehlig wrote: > > > > Locks held by virtlockd are dropped on re-exec. > > > > > > > > virtlockd 94306 POSIX 5.4G WRITE 0 0 0 /tmp/test.qcow2 > > > > virtlockd 94306 POSIX 5B WRITE 0 0 0 /run/virtlockd.pid > > > > virtlockd 94306 POSIX 5B WRITE 0 0 0 /run/virtlockd.pid > > > > > > > > Acquire locks in PostExecRestart code path. > > > > > > This is really strange and should *not* be happening. POSIX locks > > > are supposed to be preserved across execve() if the FD has CLOEXEC > > > unset, and you don't fork() before the exec. > > > > [snip] > > > > > So I wonder what we've screwed up to cause the locks to get > > > released - reaquiring them definitely isn't desirable as we > > > should not loose them in the first place ! > > > > This is really very strange. The problem seems to be the existance of > > threads at time of execve(). > > > > If you spawn a thread and the thread exits, and you execve the locks > > are preserved. > > > > If you spawn a thread and the thread is still running, and you execve > > the locks are lost. > > Indeed you are correct. I'm seeing the same behavior with the below > modifications to your demo. The lock is preserved after execve when > BREAK_FLOCK is 0, but removed when BREAK_FLOCK is 1.
I tried RHEL7 vintage kernel and saw the same behaviour, so this seems to be a fairly long standing issue. In theory we can make virNetServer single-threaded by passing max_workers==0 when creating it, but I just tried that and hit deadlock, so it seems that code has bit-rotted. If I we can fix that, then I think leaving it single threaded is the easiest way to deal with this. Failing that, we would have to arrange to cleanly terminate all threads before re-exec'ing. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
