RDMA/odp: Fix missed unlock in non-blocking invalidate_start

If invalidate_start returns with EAGAIN then the umem_rwsem needs to be
unlocked as no invalidate_end will be called.

Cc: <stable@vger.kernel.org>
Fixes: ca748c39 ("RDMA/umem: Get rid of per_mm->notifier_count")
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/core/umem_odp.c

@@ -149,6 +149,7 @@ static int ib_umem_notifier_invalidate_range_start(struct mmu_notifier *mn,
 {
 	struct ib_ucontext_per_mm *per_mm =
 		container_of(mn, struct ib_ucontext_per_mm, mn);
+	int rc;
 
 	if (mmu_notifier_range_blockable(range))
 		down_read(&per_mm->umem_rwsem);
@@ -165,11 +166,14 @@ static int ib_umem_notifier_invalidate_range_start(struct mmu_notifier *mn,
 		return 0;
 	}
 
-	return rbt_ib_umem_for_each_in_range(&per_mm->umem_tree, range->start,
+	rc = rbt_ib_umem_for_each_in_range(&per_mm->umem_tree, range->start,
 					   range->end,
 					   invalidate_range_start_trampoline,
 					   mmu_notifier_range_blockable(range),
 					   NULL);
+	if (rc)
+		up_read(&per_mm->umem_rwsem);
+	return rc;
 }
 
 static int invalidate_range_end_trampoline(struct ib_umem_odp *item, u64 start,