From ce884036d2199ebec22e4f9200789a532a1225d1 Mon Sep 17 00:00:00 2001
From: Dmitriy Vyukov <dvyukov@google.com>
Date: Tue, 28 Jan 2014 22:34:32 +0400
Subject: [PATCH] runtime: adjust malloc race instrumentation for tiny allocs
 Tiny alloc memory block is shared by different goroutines running on the same
 thread. We call racemalloc after enabling preemption in mallocgc, as the
 result another goroutine can act on not yet race-cleared tiny block. Call
 racemalloc before enabling preemption. Fixes #7224.

LGTM=dave
R=golang-codereviews, dave
CC=golang-codereviews
https://golang.org/cl/57730043
---
 src/pkg/runtime/malloc.goc                |  4 ++--
 src/pkg/runtime/race/testdata/mop_test.go | 22 ++++++++++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/pkg/runtime/malloc.goc b/src/pkg/runtime/malloc.goc
index 4e554a1f92..3dfa63dbec 100644
--- a/src/pkg/runtime/malloc.goc
+++ b/src/pkg/runtime/malloc.goc
@@ -182,6 +182,8 @@ runtime·mallocgc(uintptr size, uintptr typ, uint32 flag)
 	m->mallocing = 0;
 	if(UseSpanType && !(flag & FlagNoScan) && typ != 0 && m->settype_bufsize == nelem(m->settype_buf))
 		runtime·settype_flush(m);
+	if(raceenabled)
+		runtime·racemalloc(v, size);
 	m->locks--;
 	if(m->locks == 0 && g->preempt)  // restore the preemption request in case we've cleared it in newstack
 		g->stackguard0 = StackPreempt;
@@ -208,8 +210,6 @@ runtime·mallocgc(uintptr size, uintptr typ, uint32 flag)
 	if(!(flag & FlagNoInvokeGC) && mstats.heap_alloc >= mstats.next_gc)
 		runtime·gc(0);
 
-	if(raceenabled)
-		runtime·racemalloc(v, size);
 	return v;
 }
 
diff --git a/src/pkg/runtime/race/testdata/mop_test.go b/src/pkg/runtime/race/testdata/mop_test.go
index b0b66562cc..14591b1845 100644
--- a/src/pkg/runtime/race/testdata/mop_test.go
+++ b/src/pkg/runtime/race/testdata/mop_test.go
@@ -1933,3 +1933,25 @@ func TestRaceMethodThunk4(t *testing.T) {
 	*(*int)(d.Base) = 42
 	<-done
 }
+
+func TestNoRaceTinyAlloc(t *testing.T) {
+	const P = 4
+	const N = 1e6
+	var tinySink *byte
+	done := make(chan bool)
+	for p := 0; p < P; p++ {
+		go func() {
+			for i := 0; i < N; i++ {
+				var b byte
+				if b != 0 {
+					tinySink = &b // make it heap allocated
+				}
+				b = 42
+			}
+			done <- true
+		}()
+	}
+	for p := 0; p < P; p++ {
+		<-done
+	}
+}
-- 
2.48.1