IB/mlx4: Change vma from shared to private

Anonymous VMA (->vm_ops == NULL) cannot be shared, otherwise
it would lead to SIGBUS.

Remove the shared flags from the vma after we change it to be
anonymous.

This is easily reproduced by doing modprobe -r while running a
user-space application such as raw_ethernet_bw.

Fixes: ae184dde ('IB/mlx4_ib: Disassociate support')
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/mlx4/main.c

@@ -1187,6 +1187,8 @@ static void mlx4_ib_disassociate_ucontext(struct ib_ucontext *ibcontext)
 			BUG_ON(1);
 		}
 
+		context->hw_bar_info[i].vma->vm_flags &=
+			~(VM_SHARED | VM_MAYSHARE);
 		/* context going to be destroyed, should not access ops any more */
 		context->hw_bar_info[i].vma->vm_ops = NULL;
 	}