runtime: add memory barrier for sync send in select

Missed select case when adding the barrier last time.
All the more reason to refactor this code in Go 1.6.

Fixes #11643.

Change-Id: Ib0d19d6e0939296c0a3e06dda5e9b76f813bbc7e
Reviewed-on: https://go-review.googlesource.com/12086
Reviewed-by: Austin Clements <austin@google.com>

1 files changed, 16 insertions, 11 deletions

diff --git a/src/runtime/chan.go b/src/runtime/chan.go
index a9eb83aeb3..cfee12a551 100644
--- a/src/runtime/chan.go
+++ b/src/runtime/chan.go
@@ -165,17 +165,7 @@ func chansend(t *chantype, c *hchan, ep unsafe.Pointer, block bool, callerpc uin
 
 			recvg := sg.g
 			if sg.elem != nil {
-				// This is the only place in the entire runtime where one goroutine
-				// writes to the stack of another goroutine. The GC assumes that
-				// stack writes only happen when the goroutine is running and are
-				// only done by that goroutine. Using a write barrier is sufficient to
-				// make up for violating that assumption, but the write barrier has to work.
-				// typedmemmove will call heapBitsBulkBarrier, but the target bytes
-				// are not in the heap, so that will not help. We arrange to call
-				// memmove and typeBitsBulkBarrier instead.
-				memmove(sg.elem, ep, c.elemtype.size)
-				typeBitsBulkBarrier(c.elemtype, uintptr(sg.elem), c.elemtype.size)
-				sg.elem = nil
+				syncsend(c, sg, ep)
 			}
 			recvg.param = unsafe.Pointer(sg)
 			if sg.releasetime != 0 {
@@ -287,6 +277,21 @@ func chansend(t *chantype, c *hchan, ep unsafe.Pointer, block bool, callerpc uin
 	return true
 }
 
+func syncsend(c *hchan, sg *sudog, elem unsafe.Pointer) {
+	// Send on unbuffered channel is the only operation
+	// in the entire runtime where one goroutine
+	// writes to the stack of another goroutine. The GC assumes that
+	// stack writes only happen when the goroutine is running and are
+	// only done by that goroutine. Using a write barrier is sufficient to
+	// make up for violating that assumption, but the write barrier has to work.
+	// typedmemmove will call heapBitsBulkBarrier, but the target bytes
+	// are not in the heap, so that will not help. We arrange to call
+	// memmove and typeBitsBulkBarrier instead.
+	memmove(sg.elem, elem, c.elemtype.size)
+	typeBitsBulkBarrier(c.elemtype, uintptr(sg.elem), c.elemtype.size)
+	sg.elem = nil
+}
+
 func closechan(c *hchan) {
 	if c == nil {
 		panic("close of nil channel")