3 files changed, 28 insertions, 22 deletions
diff --git a/src/runtime/chan.go b/src/runtime/chan.go
index f6f4ffd02e..0afe5d962b 100644
--- a/src/runtime/chan.go
+++ b/src/runtime/chan.go
@@ -263,18 +263,19 @@ func chansend(c *hchan, ep unsafe.Pointer, block bool, callerpc uintptr) bool {
 	}
 	gp.waiting = nil
 	gp.activeStackChans = false
-	if gp.param == nil {
-		if c.closed == 0 {
-			throw("chansend: spurious wakeup")
-		}
-		panic(plainError("send on closed channel"))
-	}
+	closed := !mysg.success
 	gp.param = nil
 	if mysg.releasetime > 0 {
 		blockevent(mysg.releasetime-t0, 2)
 	}
 	mysg.c = nil
 	releaseSudog(mysg)
+	if closed {
+		if c.closed == 0 {
+			throw("chansend: spurious wakeup")
+		}
+		panic(plainError("send on closed channel"))
+	}
 	return true
 }
 
@@ -311,6 +312,7 @@ func send(c *hchan, sg *sudog, ep unsafe.Pointer, unlockf func(), skip int) {
 	gp := sg.g
 	unlockf()
 	gp.param = unsafe.Pointer(sg)
+	sg.success = true
 	if sg.releasetime != 0 {
 		sg.releasetime = cputicks()
 	}
@@ -384,7 +386,8 @@ func closechan(c *hchan) {
 			sg.releasetime = cputicks()
 		}
 		gp := sg.g
-		gp.param = nil
+		gp.param = unsafe.Pointer(sg)
+		sg.success = false
 		if raceenabled {
 			raceacquireg(gp, c.raceaddr())
 		}
@@ -402,7 +405,8 @@ func closechan(c *hchan) {
 			sg.releasetime = cputicks()
 		}
 		gp := sg.g
-		gp.param = nil
+		gp.param = unsafe.Pointer(sg)
+		sg.success = false
 		if raceenabled {
 			raceacquireg(gp, c.raceaddr())
 		}
@@ -575,11 +579,11 @@ func chanrecv(c *hchan, ep unsafe.Pointer, block bool) (selected, received bool)
 	if mysg.releasetime > 0 {
 		blockevent(mysg.releasetime-t0, 2)
 	}
-	closed := gp.param == nil
+	success := mysg.success
 	gp.param = nil
 	mysg.c = nil
 	releaseSudog(mysg)
-	return true, !closed
+	return true, success
 }
 
 // recv processes a receive operation on a full channel c.
@@ -632,6 +636,7 @@ func recv(c *hchan, sg *sudog, ep unsafe.Pointer, unlockf func(), skip int) {
 	gp := sg.g
 	unlockf()
 	gp.param = unsafe.Pointer(sg)
+	sg.success = true
 	if sg.releasetime != 0 {
 		sg.releasetime = cputicks()
 	}
diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index 959878400d..b7d0739e54 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -366,6 +366,12 @@ type sudog struct {
 	// g.selectDone must be CAS'd to win the wake-up race.
 	isSelect bool
 
+	// success indicates whether communication over channel c
+	// succeeded. It is true if the goroutine was awoken because a
+	// value was delivered over channel c, and false if awoken
+	// because c was closed.
+	success bool
+
 	parent   *sudog // semaRoot binary tree
 	waitlink *sudog // g.waiting list or semaRoot
 	waittail *sudog // semaRoot
diff --git a/src/runtime/select.go b/src/runtime/select.go
index a069e3e050..081db7bad4 100644
--- a/src/runtime/select.go
+++ b/src/runtime/select.go
@@ -221,12 +221,12 @@ func selectgo(cas0 *scase, order0 *uint16, ncases int) (int, bool) {
 		nextp  **sudog
 	)
 
-loop:
 	// pass 1 - look for something already waiting
 	var dfli int
 	var dfl *scase
 	var casi int
 	var cas *scase
+	var caseSuccess bool
 	var recvOK bool
 	for i := 0; i < ncases; i++ {
 		casi = int(pollorder[i])
@@ -331,6 +331,7 @@ loop:
 	// We singly-linked up the SudoGs in lock order.
 	casi = -1
 	cas = nil
+	caseSuccess = false
 	sglist = gp.waiting
 	// Clear all elem before unlinking from gp.waiting.
 	for sg1 := gp.waiting; sg1 != nil; sg1 = sg1.waitlink {
@@ -352,6 +353,7 @@ loop:
 			// sg has already been dequeued by the G that woke us up.
 			casi = int(casei)
 			cas = k
+			caseSuccess = sglist.success
 		} else {
 			c = k.c
 			if k.kind == caseSend {
@@ -367,16 +369,7 @@ loop:
 	}
 
 	if cas == nil {
-		// We can wake up with gp.param == nil (so cas == nil)
-		// when a channel involved in the select has been closed.
-		// It is easiest to loop and re-run the operation;
-		// we'll see that it's now closed.
-		// Maybe some day we can signal the close explicitly,
-		// but we'd have to distinguish close-on-reader from close-on-writer.
-		// It's easiest not to duplicate the code and just recheck above.
-		// We know that something closed, and things never un-close,
-		// so we won't block again.
-		goto loop
+		throw("selectgo: bad wakeup")
 	}
 
 	c = cas.c
@@ -386,7 +379,9 @@ loop:
 	}
 
 	if cas.kind == caseRecv {
-		recvOK = true
+		recvOK = caseSuccess
+	} else if cas.kind == caseSend && !caseSuccess {
+		goto sclose
 	}
 
 	if raceenabled {