RDMA/umem: Restore lockdep check while downgrading lock

Lockdep engine handles correctly downgrade of locks and it simply
incorrect to disable lockdep checks prior to calling mmu_notifier.

Remove lockdep_off and ensure locks correctness.
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/umem_odp.c

@@ -431,13 +431,7 @@ int ib_umem_odp_get(struct ib_ucontext *context, struct ib_umem *umem,
 		atomic_set(&context->notifier_count, 0);
 		INIT_HLIST_NODE(&context->mn.hlist);
 		context->mn.ops = &ib_umem_notifiers;
-		/*
-		 * Lock-dep detects a false positive for mmap_sem vs.
-		 * umem_rwsem, due to not grasping downgrade_write correctly.
-		 */
-		lockdep_off();
 		ret_val = mmu_notifier_register(&context->mn, mm);
-		lockdep_on();
 		if (ret_val) {
 			pr_err("Failed to register mmu_notifier %d\n", ret_val);
 			ret_val = -EBUSY;