mount.cifs hangs and becomes unresponsive
This problem has been around for at least 10 years, and there still seems to be no way to fix it. I've tried umount -l xxx, which doesn't hang, but then we do hang when trying to mount the share. One problem seems to be that you need to remount the share before any process tries to open a file on it. This can be very tricky if you have soft-links pointing into the shared file system.
Even crazier: If the system is stuck, smbmount still works without a hitch, even as the mount on the same volume is hung for more than 10 minutes.