ipc: drop ipc_lock_by_ptr

After previous cleanups and optimizations, this function is no longer
heavily used and we don't have a good reason to keep it.  Update the few
remaining callers and get rid of it.

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/ipc/util.c b/ipc/util.c
index 1ddadcf..9f6aa30 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -205,7 +205,8 @@
 			continue;
 		}
 
-		ipc_lock_by_ptr(ipc);
+		rcu_read_lock();
+		ipc_lock_object(ipc);
 		return ipc;
 	}
 
@@ -838,7 +839,8 @@
 		ipc = idr_find(&ids->ipcs_idr, pos);
 		if (ipc != NULL) {
 			*new_pos = pos + 1;
-			ipc_lock_by_ptr(ipc);
+			rcu_read_lock();
+			ipc_lock_object(ipc);
 			return ipc;
 		}
 	}