From bc805795bd28ae4cd1a70b3053a3a71668bfef87 Mon Sep 17 00:00:00 2001
From: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Date: Wed, 17 Aug 2022 17:36:12 +0700
Subject: [PATCH] runtime: convert m.preemptGen to atomic type

Updates #53821

Change-Id: I134dac3b1eb35f2da00e5ef8f4c264f08d4f65b6
Reviewed-on: https://go-review.googlesource.com/c/go/+/423887
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
---
 src/runtime/os_windows.go  | 8 ++++----
 src/runtime/preempt.go     | 5 ++---
 src/runtime/runtime2.go    | 4 ++--
 src/runtime/signal_unix.go | 2 +-
 4 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/src/runtime/os_windows.go b/src/runtime/os_windows.go
index 2f6ec75cf89..54261d6fc02 100644
--- a/src/runtime/os_windows.go
+++ b/src/runtime/os_windows.go
@@ -1326,7 +1326,7 @@ func preemptM(mp *m) {
 	if !atomic.Cas(&mp.preemptExtLock, 0, 1) {
 		// External code is running. Fail the preemption
 		// attempt.
-		atomic.Xadd(&mp.preemptGen, 1)
+		mp.preemptGen.Add(1)
 		return
 	}
 
@@ -1336,7 +1336,7 @@ func preemptM(mp *m) {
 		// The M hasn't been minit'd yet (or was just unminit'd).
 		unlock(&mp.threadLock)
 		atomic.Store(&mp.preemptExtLock, 0)
-		atomic.Xadd(&mp.preemptGen, 1)
+		mp.preemptGen.Add(1)
 		return
 	}
 	var thread uintptr
@@ -1366,7 +1366,7 @@ func preemptM(mp *m) {
 		atomic.Store(&mp.preemptExtLock, 0)
 		// The thread no longer exists. This shouldn't be
 		// possible, but just acknowledge the request.
-		atomic.Xadd(&mp.preemptGen, 1)
+		mp.preemptGen.Add(1)
 		return
 	}
 
@@ -1431,7 +1431,7 @@ func preemptM(mp *m) {
 	atomic.Store(&mp.preemptExtLock, 0)
 
 	// Acknowledge the preemption.
-	atomic.Xadd(&mp.preemptGen, 1)
+	mp.preemptGen.Add(1)
 
 	stdcall1(_ResumeThread, thread)
 	stdcall1(_CloseHandle, thread)
diff --git a/src/runtime/preempt.go b/src/runtime/preempt.go
index da24f5042c0..dae417215fd 100644
--- a/src/runtime/preempt.go
+++ b/src/runtime/preempt.go
@@ -55,7 +55,6 @@ package runtime
 import (
 	"internal/abi"
 	"internal/goarch"
-	"runtime/internal/atomic"
 )
 
 type suspendGState struct {
@@ -192,7 +191,7 @@ func suspendG(gp *g) suspendGState {
 		case _Grunning:
 			// Optimization: if there is already a pending preemption request
 			// (from the previous loop iteration), don't bother with the atomics.
-			if gp.preemptStop && gp.preempt && gp.stackguard0 == stackPreempt && asyncM == gp.m && atomic.Load(&asyncM.preemptGen) == asyncGen {
+			if gp.preemptStop && gp.preempt && gp.stackguard0 == stackPreempt && asyncM == gp.m && asyncM.preemptGen.Load() == asyncGen {
 				break
 			}
 
@@ -208,7 +207,7 @@ func suspendG(gp *g) suspendGState {
 
 			// Prepare for asynchronous preemption.
 			asyncM2 := gp.m
-			asyncGen2 := atomic.Load(&asyncM2.preemptGen)
+			asyncGen2 := asyncM2.preemptGen.Load()
 			needAsync := asyncM != asyncM2 || asyncGen != asyncGen2
 			asyncM = asyncM2
 			asyncGen = asyncGen2
diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index 3cf0e8e98b5..63ba5348158 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -583,8 +583,8 @@ type m struct {
 
 	// preemptGen counts the number of completed preemption
 	// signals. This is used to detect when a preemption is
-	// requested, but fails. Accessed atomically.
-	preemptGen uint32
+	// requested, but fails.
+	preemptGen atomic.Uint32
 
 	// Whether this is a pending preemption signal on this M.
 	signalPending atomic.Uint32
diff --git a/src/runtime/signal_unix.go b/src/runtime/signal_unix.go
index 4c3f43a819a..545094c6403 100644
--- a/src/runtime/signal_unix.go
+++ b/src/runtime/signal_unix.go
@@ -349,7 +349,7 @@ func doSigPreempt(gp *g, ctxt *sigctxt) {
 	}
 
 	// Acknowledge the preemption.
-	atomic.Xadd(&gp.m.preemptGen, 1)
+	gp.m.preemptGen.Add(1)
 	gp.m.signalPending.Store(0)
 
 	if GOOS == "darwin" || GOOS == "ios" {