animals really need call_rcu after all

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
update answer to ex2

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
update ex2

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Update exercises

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Add ex3

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>