The variable 'err' is assgigned to an error message if atomic alloc
failed, while it has no chance to be printed if is_atomic is true.

Here change to print error message too if atomic alloc failed, while
avoid to call dump_stack() if that case.
Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Dennis Zhou <dennis@kernel.org>