code review 133470043: runtime: avoid race with forcegc helper

src/pkg/runtime/proc.c

Index: src/pkg/runtime/proc.c
===================================================================
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -2846,9 +2846,12 @@
 		lastgc = runtime·atomicload64(&mstats.last_gc);
 		if(lastgc != 0 && unixnow - lastgc > forcegcperiod && runtime·atomicload(&runtime·forcegc.idle)) {
 			runtime·lock(&runtime·forcegc.lock);
-			runtime·forcegc.idle = 0;
-			runtime·forcegc.g->schedlink = nil;
-			injectglist(runtime·forcegc.g);
+			if(runtime·forcegc.g != nil) {

[dvyukov, 2014/09/03 03:44:15]

there is no race here

this code is executed only when forcegc.idle==1; forcegc.idle is set only when
forcegc.g is already set
so this just increases level of indentation and makes reader think that
forcegc.g somehow can be nil here

+				// Goroutine may be started but has not initialized g yet.
+				runtime·forcegc.idle = 0;
+				runtime·forcegc.g->schedlink = nil;
+				injectglist(runtime·forcegc.g);
+			}
 			runtime·unlock(&runtime·forcegc.lock);
 		}