src/runtime/stack1.go | 6 ++++++

diff --git a/src/runtime/stack1.go b/src/runtime/stack1.go
index efcb5f25fada67a8a95445fe477c30e36fbfabcd..19634ef6d58a12d57b683c2615e6460ec92b748e 100644
--- a/src/runtime/stack1.go
+++ b/src/runtime/stack1.go
@@ -609,6 +609,10 @@ 	if stackDebug >= 1 {
 		print("copystack gp=", gp, " [", hex(old.lo), " ", hex(old.hi-used), " ", hex(old.hi), "]/", gp.stackAlloc, " -> [", hex(new.lo), " ", hex(new.hi-used), " ", hex(new.hi), "]/", newsize, "\n")
 	}
 
+	// Disallow sigprof scans of this stack and block if there's
+	// one in progress.
+	gcLockStackBarriers(gp)
+
 	// adjust pointers in the to-be-copied frames
 	var adjinfo adjustinfo
 	adjinfo.old = old
@@ -639,6 +643,8 @@ 	gp.sched.sp = new.hi - used
 	oldsize := gp.stackAlloc
 	gp.stackAlloc = newsize
 	gp.stkbar = newstkbar
+
+	gcUnlockStackBarriers(gp)
 
 	// free old stack
 	if stackPoisonCopy != 0 {