Using raw pointers when passing an object as a function argument

Imagine following scenario

I have a classes A and B

/* A class with a shared pointer */
class A {
public:
  //...

private:
  std::shared_ptr<object_t> m_ptr;
};

/* A class with an unique pointer */
class B {
public:
  //...

private:
  std::unique_ptr<object_t> m_ptr;
};

I want to have a function, which will use the object pointed by m_ptr and process it, but will not take ownership of it. Should the function take a smart pointer as an argument like

void process(std::shared_ptr<object_t> obj);

or should it use a raw pointer like

void process(object_t* obj);

Edit:

Apparently, I forgot about an important 3rd option for the function

void process(object_t& obj);

which as pointed out by kotatsuyaki should be the preferred solution.