runtime: check channel's elemsize before calling race detector

When c.elemsize==0 we call raceacquire() and racerelease()
as opposed to calling racereleaseacquire()

The reason for this change is that, when elemsize==0, we don't
allocate a full buffer for the channel.  Instead of individual
buffer entries, the race detector uses the c.buf as the only
buffer entry.  This simplification prevents us following the
memory model's happens-before rules implemented in racereleaseacquire().
So, instead of calling racereleaseacquire(), we accumulate
happens-before information in the synchronization object associated
with c.buf.

The functionality in this change is implemented in a new function
called racenotify()

Fixes #42598

Change-Id: I75b92708633fdfde658dc52e06264e2171824e51
Reviewed-on: https://go-review.googlesource.com/c/go/+/271987
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Dmitry Vyukov <dvyukov@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Ian Lance Taylor <iant@golang.org>

1 files changed, 22 insertions, 0 deletions

diff --git a/src/runtime/race/testdata/chan_test.go b/src/runtime/race/testdata/chan_test.go
index 3e57b8221c..e39ad4f99c 100644
--- a/src/runtime/race/testdata/chan_test.go
+++ b/src/runtime/race/testdata/chan_test.go
@@ -763,3 +763,25 @@ func TestNoRaceCloseHappensBeforeRead(t *testing.T) {
 		<-read
 	}
 }
+
+// Test that we call the proper race detector function when c.elemsize==0.
+// See https://github.com/golang/go/issues/42598
+func TestNoRaceElemetSize0(t *testing.T) {
+	var x, y int
+	var c = make(chan struct{}, 2)
+	c <- struct{}{}
+	c <- struct{}{}
+	go func() {
+		x += 1
+		<-c
+	}()
+	go func() {
+		y += 1
+		<-c
+	}()
+	time.Sleep(10 * time.Millisecond)
+	c <- struct{}{}
+	c <- struct{}{}
+	x += 1
+	y += 1
+}