Hi,

the attached patch should fix the combination of CLONE_NEWIPC with 
shared sysv undo structures (the common case, just 
sys_unshare(CLONE_NEWIPC)):
lookup_undo() now locates the undo array based on both semid and the 
namespace pointer.
Additionally, the patch tries to clean the code up by using the linked 
list macros from <linux/list.h> instead of single linked lists.

The patch passes a few quick tests, I'm interested in feedback. Are 
there test apps for testing the IPC namespace code?

--
    Manfred