Merge pull request #516 from jamesmunns/patch-1

Update critical_section.rs

Author: adamgreig

Diff for: cortex-m/src/critical_section.rs

@@ -9,13 +9,16 @@ set_impl!(SingleCoreCriticalSection);
 unsafe impl Impl for SingleCoreCriticalSection {
     unsafe fn acquire() -> RawRestoreState {
         let was_active = primask::read().is_active();
+        // NOTE: Fence guarantees are provided by interrupt::disable(), which performs a `compiler_fence(SeqCst)`.
         interrupt::disable();
         was_active
     }
 
     unsafe fn release(was_active: RawRestoreState) {
         // Only re-enable interrupts if they were enabled before the critical section.
         if was_active {
+            // NOTE: Fence guarantees are provided by interrupt::enable(), which performs a
+            // `compiler_fence(SeqCst)`.
             interrupt::enable()
         }
     }