ipc: drop ipc_lock()

ipc/util.c contains multiple functions to get the ipc object pointer given
an id number.

There are two sets of function: One set verifies the sequence counter part
of the id number, other functions do not check the sequence counter.

The standard for function names in ipc/util.c is
- ..._check() functions verify the sequence counter
- ..._idr() functions do not verify the sequence counter

ipc_lock() is an exception: It does not verify the sequence counter value,
but this is not obvious from the function name.

Furthermore, shm.c is the only user of this helper.  Thus, we can simply
move the logic into shm_lock() and get rid of the function altogether.

[[email protected]: most of changelog]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Davidlohr Bueso <[email protected]>
Signed-off-by: Manfred Spraul <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Herbert Xu <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Michael Kerrisk <[email protected]>
Cc: Michal Hocko <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

ipc/util.h

@@ -142,7 +142,6 @@ int ipc_rcu_getref(struct kern_ipc_perm *ptr);
 void ipc_rcu_putref(struct kern_ipc_perm *ptr,
 			void (*func)(struct rcu_head *head));
 
-struct kern_ipc_perm *ipc_lock(struct ipc_ids *, int);
 struct kern_ipc_perm *ipc_obtain_object_idr(struct ipc_ids *ids, int id);
 
 void kernel_to_ipc64_perm(struct kern_ipc_perm *in, struct ipc64_perm *out);