+ /// **What it does:** Checks for usages of `Mutex<X>` where an atomic will do.
+ ///
+ /// **Why is this bad?** Using a mutex just to make access to a plain bool or
+ /// reference sequential is shooting flies with cannons.
+ /// `std::sync::atomic::AtomicBool` and `std::sync::atomic::AtomicPtr` are leaner and
+ /// faster.
+ ///
+ /// **Known problems:** This lint cannot detect if the mutex is actually used
+ /// for waiting before a critical section.
+ ///
+ /// **Example:**
+ /// ```rust
+ /// # use std::sync::Mutex;
+ /// # let y = 1;
+ /// let x = Mutex::new(&y);
+ /// ```