Hi,

below is the second attempt to fix SEM_UNDO + unshare():
lookup_undo (in ipc/sem.c) is not namespace-aware, thus all entries in 
sysvsem.undo_list must be from the same namespace.
The patch enforces that by detaching the current thread from 
sysvsem.undo_list in switch_task_namespaces() if the ipc namespace is 
changed.

The patch boots and passes simple sysvsem+unshare tests.

Signed-Off-By: Manfred Spraul <manfred@colorfullife.com>