diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index 886f7bdca9..0c71c3cfab 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -1985,10 +1985,10 @@ func needm(signal bool) {
 	sigsave(&sigmask)
 	sigblock(false)
 
-	// nilokay=false is safe here because of the invariant above,
+	// getExtraM is safe here because of the invariant above,
 	// that the extra list always contains or will soon contain
 	// at least one m.
-	mp, last := getExtraM(false)
+	mp, last := getExtraM()
 
 	// Set needextram when we've just emptied the list,
 	// so that the eventual call into cgocallbackg will
@@ -2260,7 +2260,6 @@ func lockextra(nilokay bool) *m {
 			continue
 		}
 		if extraM.CompareAndSwap(old, locked) {
-			extraMInUse.Add(1)
 			return (*m)(unsafe.Pointer(old))
 		}
 		osyield_no_g()
@@ -2277,13 +2276,13 @@ func unlockextra(mp *m, delta int32) {
 // Return an M from the extra M list. Returns last == true if the list becomes
 // empty because of this call.
 //
+// Spins waiting for an extra M, so caller must ensure that the list always
+// contains or will soon contain at least one M.
+//
 //go:nosplit
-func getExtraM(nilokay bool) (mp *m, last bool) {
-	mp = lockextra(nilokay)
-	if mp == nil {
-		unlockextra(nil, 0)
-		return nil, true
-	}
+func getExtraM() (mp *m, last bool) {
+	mp = lockextra(false)
+	extraMInUse.Add(1)
 	unlockextra(mp.schedlink.ptr(), -1)
 	return mp, mp.schedlink.ptr() == nil
 }
diff --git a/src/runtime/testdata/testprogcgo/callback.go b/src/runtime/testdata/testprogcgo/callback.go
index 25f07159b8..319572fe10 100644
--- a/src/runtime/testdata/testprogcgo/callback.go
+++ b/src/runtime/testdata/testprogcgo/callback.go
@@ -32,6 +32,8 @@ import (
 	"fmt"
 	"os"
 	"runtime"
+	"sync/atomic"
+	_ "unsafe" // for go:linkname
 )
 
 func init() {
@@ -40,6 +42,11 @@ func init() {
 
 //export go_callback
 func go_callback() {
+	if e := extraMInUse.Load(); e == 0 {
+		fmt.Printf("in callback extraMInUse got %d want >0\n", e)
+		os.Exit(1)
+	}
+
 	runtime.GC()
 	grow()
 	runtime.GC()
@@ -69,6 +76,12 @@ func CgoCallbackGC() {
 	if os.Getenv("RUNTIME_TEST_SHORT") != "" {
 		P = 10
 	}
+
+	if e := extraMInUse.Load(); e != 0 {
+		fmt.Printf("before testing extraMInUse got %d want 0\n", e)
+		os.Exit(1)
+	}
+
 	done := make(chan bool)
 	// allocate a bunch of stack frames and spray them with pointers
 	for i := 0; i < P; i++ {
@@ -90,5 +103,14 @@ func CgoCallbackGC() {
 	for i := 0; i < P; i++ {
 		<-done
 	}
+
+	if e := extraMInUse.Load(); e != 0 {
+		fmt.Printf("after testing extraMInUse got %d want 0\n", e)
+		os.Exit(1)
+	}
+
 	fmt.Printf("OK\n")
 }
+
+//go:linkname extraMInUse runtime.extraMInUse
+var extraMInUse atomic.Uint32