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diff --git a/src/tools/clippy/src/docs/rc_mutex.txt b/src/tools/clippy/src/docs/rc_mutex.txt
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+### What it does
+Checks for `Rc<Mutex<T>>`.
+
+### Why is this bad?
+`Rc` is used in single thread and `Mutex` is used in multi thread.
+Consider using `Rc<RefCell<T>>` in single thread or `Arc<Mutex<T>>` in multi thread.
+
+### Known problems
+Sometimes combining generic types can lead to the requirement that a
+type use Rc in conjunction with Mutex. We must consider those cases false positives, but
+alas they are quite hard to rule out. Luckily they are also rare.
+
+### Example
+```
+use std::rc::Rc;
+use std::sync::Mutex;
+fn foo(interned: Rc<Mutex<i32>>) { ... }
+```
+
+Better:
+
+```
+use std::rc::Rc;
+use std::cell::RefCell
+fn foo(interned: Rc<RefCell<i32>>) { ... }
+```
+\ No newline at end of file