Hi,

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().

Andrew, could you add it to -mm?

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