diff --git a/drivers/infiniband/hw/hfi1/mmu_rb.c b/drivers/infiniband/hw/hfi1/mmu_rb.c
index 876cc78a22cca16e2ff184fc73daf0a1e89dc9e0..7333646021bb809d4b60908456eb9f01c5f1ab4f 100644
--- a/drivers/infiniband/hw/hfi1/mmu_rb.c
+++ b/drivers/infiniband/hw/hfi1/mmu_rb.c
@@ -80,6 +80,9 @@ void hfi1_mmu_rb_unregister(struct mmu_rb_handler *handler)
 	unsigned long flags;
 	struct list_head del_list;
 
+	/* Prevent freeing of mm until we are completely finished. */
+	mmgrab(handler->mn.mm);
+
 	/* Unregister first so we don't get any more notifications. */
 	mmu_notifier_unregister(&handler->mn, handler->mn.mm);
 
@@ -102,6 +105,9 @@ void hfi1_mmu_rb_unregister(struct mmu_rb_handler *handler)
 
 	do_remove(handler, &del_list);
 
+	/* Now the mm may be freed. */
+	mmdrop(handler->mn.mm);
+
 	kfree(handler);
 }