Re: [libvirt] [PATCH] virtlockd: acquire locks on re-exec

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.