runtime: add race annotations to cbs.lock

cbs.lock protects a map. The map implementation is race instrumented
regardless of which package is it called from.

lock/unlock are not automatically race instrumented, so we can trigger
race false positives without manually annotating our lock acquire and
release.

compileCallback is used during initialization before the P is available,
at which point raceacquire will crash during a racecallback to get the
race proc. Thus we skip instrumentation until scheduler initialization
is complete.

Fixes #50249.

Change-Id: Ie49227c9e9210ffbf0aee65f86f2b7b6a2f64638
Reviewed-on: https://go-review.googlesource.com/c/go/+/414518
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>

src/runtime/syscall_windows.go

@@ -12,12 +12,30 @@ import (
 
 // cbs stores all registered Go callbacks.
 var cbs struct {
-	lock  mutex
+	lock  mutex // use cbsLock / cbsUnlock for race instrumentation.
 	ctxt  [cb_max]winCallback
 	index map[winCallbackKey]int
 	n     int
 }
 
+func cbsLock() {
+	lock(&cbs.lock)
+	// compileCallback is used by goenvs prior to completion of schedinit.
+	// raceacquire involves a racecallback to get the proc, which is not
+	// safe prior to scheduler initialization. Thus avoid instrumentation
+	// until then.
+	if raceenabled && mainStarted {
+		raceacquire(unsafe.Pointer(&cbs.lock))
+	}
+}
+
+func cbsUnlock() {
+	if raceenabled && mainStarted {
+		racerelease(unsafe.Pointer(&cbs.lock))
+	}
+	unlock(&cbs.lock)
+}
+
 // winCallback records information about a registered Go callback.
 type winCallback struct {
 	fn     *funcval // Go function
@@ -302,11 +320,11 @@ func compileCallback(fn eface, cdecl bool) (code uintptr) {
 
 	key := winCallbackKey{(*funcval)(fn.data), cdecl}
 
-	lock(&cbs.lock) // We don't unlock this in a defer because this is used from the system stack.
+	cbsLock()
 
 	// Check if this callback is already registered.
 	if n, ok := cbs.index[key]; ok {
-		unlock(&cbs.lock)
+		cbsUnlock()
 		return callbackasmAddr(n)
 	}
 
@@ -316,7 +334,7 @@ func compileCallback(fn eface, cdecl bool) (code uintptr) {
 	}
 	n := cbs.n
 	if n >= len(cbs.ctxt) {
-		unlock(&cbs.lock)
+		cbsUnlock()
 		throw("too many callback functions")
 	}
 	c := winCallback{key.fn, retPop, abiMap}
@@ -324,7 +342,7 @@ func compileCallback(fn eface, cdecl bool) (code uintptr) {
 	cbs.index[key] = n
 	cbs.n++
 
-	unlock(&cbs.lock)
+	cbsUnlock()
 	return callbackasmAddr(n)
 }