diff --git a/ipc/shm.c b/ipc/shm.c
index e7d5107..c6b4ad5 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -757,31 +757,42 @@
 			return -EFAULT;
 	}
 
+	down_write(&shm_ids(ns).rw_mutex);
+	rcu_read_lock();
+
 	ipcp = ipcctl_pre_down(ns, &shm_ids(ns), shmid, cmd,
 			       &shmid64.shm_perm, 0);
-	if (IS_ERR(ipcp))
-		return PTR_ERR(ipcp);
+	if (IS_ERR(ipcp)) {
+		err = PTR_ERR(ipcp);
+		/* the ipc lock is not held upon failure */
+		goto out_unlock1;
+	}
 
 	shp = container_of(ipcp, struct shmid_kernel, shm_perm);
 
 	err = security_shm_shmctl(shp, cmd);
 	if (err)
-		goto out_unlock;
+		goto out_unlock0;
+
 	switch (cmd) {
 	case IPC_RMID:
+		/* do_shm_rmid unlocks the ipc object and rcu */
 		do_shm_rmid(ns, ipcp);
 		goto out_up;
 	case IPC_SET:
 		err = ipc_update_perm(&shmid64.shm_perm, ipcp);
 		if (err)
-			goto out_unlock;
+			goto out_unlock0;
 		shp->shm_ctim = get_seconds();
 		break;
 	default:
 		err = -EINVAL;
 	}
-out_unlock:
-	shm_unlock(shp);
+
+out_unlock0:
+	ipc_unlock_object(&shp->shm_perm);
+out_unlock1:
+	rcu_read_unlock();
 out_up:
 	up_write(&shm_ids(ns).rw_mutex);
 	return err;