actually, reentrant uninitialized mutex acquisition is outright UB

1 files changed, 2 insertions, 3 deletions

diff --git a/src/libstd/thread/mod.rs b/src/libstd/thread/mod.rs
index 98b4ca36c26..0078a05e597 100644
--- a/src/libstd/thread/mod.rs
+++ b/src/libstd/thread/mod.rs
@@ -940,9 +940,8 @@ pub struct ThreadId(u64);
 impl ThreadId {
     // Generate a new unique thread ID.
     fn new() -> ThreadId {
-        // `GUARD` is never initialized fully, so this mutex is reentrant!
-        // Do not use it in a way that might be reentrant, that could lead to
-        // aliasing `&mut`.
+        // `GUARD` is never initialized fully, so it is UB to attempt to
+        // acquire this mutex reentrantly!
         static GUARD: mutex::Mutex = mutex::Mutex::new();
         static mut COUNTER: u64 = 0;