Closing of an event channel in the Linux kernel can result in a deadlock. This happens when the close is being performed in parallel to an unrelated Xen console action and the handling of a Xen console interrupt in an unprivileged guest. The closing of an event channel is e.g. triggered by removal of a paravirtual device on the other side. As this action will cause console messages to be issued on the other side quite often, the chance of triggering the deadlock is not neglectable.
A (malicious) guest administrator could cause a denial of service (DoS) in a backend domain (other than dom0) by disabling a paravirtualized device. A malicious backend could cause DoS in a guest running a Linux kernel by disabling a paravirtualized device.