diff --git a/ipc/sem.c b/ipc/sem.c
index bc3d530..a37aaeb 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -2074,17 +2074,28 @@
 		rcu_read_lock();
 		un = list_entry_rcu(ulp->list_proc.next,
 				    struct sem_undo, list_proc);
-		if (&un->list_proc == &ulp->list_proc)
-			semid = -1;
-		 else
-			semid = un->semid;
-
-		if (semid == -1) {
+		if (&un->list_proc == &ulp->list_proc) {
+			/*
+			 * We must wait for freeary() before freeing this ulp,
+			 * in case we raced with last sem_undo. There is a small
+			 * possibility where we exit while freeary() didn't
+			 * finish unlocking sem_undo_list.
+			 */
+			spin_unlock_wait(&ulp->lock);
 			rcu_read_unlock();
 			break;
 		}
+		spin_lock(&ulp->lock);
+		semid = un->semid;
+		spin_unlock(&ulp->lock);
 
-		sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, un->semid);
+		/* exit_sem raced with IPC_RMID, nothing to do */
+		if (semid == -1) {
+			rcu_read_unlock();
+			continue;
+		}
+
+		sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, semid);
 		/* exit_sem raced with IPC_RMID, nothing to do */
 		if (IS_ERR(sma)) {
 			rcu_read_unlock();