ipc/sem.c: convert to use built-in RCU list checking

CONFIG_PROVE_RCU_LIST requires list_for_each_entry_rcu() to pass a lockdep
expression if using srcu or locking for protection.  It can only check
regular RCU protection, all other protection needs to be passed as lockdep
expression.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Joel Fernandes (Google) <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: "Gustavo A. R. Silva" <[email protected]>
Cc: Jonathan Derrick <[email protected]>
Cc: Keith Busch <[email protected]>
Cc: Lorenzo Pieralisi <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

ipc/sem.c

@@ -1852,7 +1852,8 @@ static struct sem_undo *__lookup_undo(struct sem_undo_list *ulp, int semid)
 {
 	struct sem_undo *un;
 
-	list_for_each_entry_rcu(un, &ulp->list_proc, list_proc) {
+	list_for_each_entry_rcu(un, &ulp->list_proc, list_proc,
+				spin_is_locked(&ulp->lock)) {
 		if (un->semid == semid)
 			return un;
 	}