Comment flock usage on Linux

1 files changed, 5 insertions, 0 deletions

diff --git a/src/librustc_data_structures/flock.rs b/src/librustc_data_structures/flock.rs
index 655248e0f52..9383be474fd 100644
--- a/src/librustc_data_structures/flock.rs
+++ b/src/librustc_data_structures/flock.rs
@@ -12,6 +12,11 @@ use std::io;
 use std::path::Path;
 
 cfg_if! {
+    // We use `flock` rather than `fcntl` on Linux, because WSL1 does not support
+    // `fcntl`-style advisory locks properly (rust-lang/rust#72157).
+    //
+    // For other Unix targets we still use `fcntl` because it's more portable than
+    // `flock`.
     if #[cfg(target_os = "linux")] {
         use std::os::unix::prelude::*;