The lifetime of the ipc objects (sem array, msg queue, shm mapping) is
controlled by kern_ipc_perms->lock - a spinlock.  There is no simple way to
reacquire this spinlock after it was dropped to
schedule()/kmalloc/copy_{to,from}_user/whatever.

The attached patch adds a reference count as a preparation to get rid of
sem_revalidate().
Signed-Off-By: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>