runtime: convert g.parkingOnChan to atomic type

Updates #53821

Change-Id: I54de39b984984fb3c160aba5afacb90131fd47c4
Reviewed-on: https://go-review.googlesource.com/c/go/+/424394
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>

src/runtime/chan.go

@@ -255,7 +255,7 @@ func chansend(c *hchan, ep unsafe.Pointer, block bool, callerpc uintptr) bool {
 	// to park on a channel. The window between when this G's status
 	// changes and when we set gp.activeStackChans is not safe for
 	// stack shrinking.
-	atomic.Store8(&gp.parkingOnChan, 1)
+	gp.parkingOnChan.Store(true)
 	gopark(chanparkcommit, unsafe.Pointer(&c.lock), waitReasonChanSend, traceEvGoBlockSend, 2)
 	// Ensure the value being sent is kept alive until the
 	// receiver copies it out. The sudog has a pointer to the
@@ -579,7 +579,7 @@ func chanrecv(c *hchan, ep unsafe.Pointer, block bool) (selected, received bool)
 	// to park on a channel. The window between when this G's status
 	// changes and when we set gp.activeStackChans is not safe for
 	// stack shrinking.
-	atomic.Store8(&gp.parkingOnChan, 1)
+	gp.parkingOnChan.Store(true)
 	gopark(chanparkcommit, unsafe.Pointer(&c.lock), waitReasonChanReceive, traceEvGoBlockRecv, 2)
 
 	// someone woke us up
@@ -664,7 +664,7 @@ func chanparkcommit(gp *g, chanLock unsafe.Pointer) bool {
 	// Mark that it's safe for stack shrinking to occur now,
 	// because any thread acquiring this G's stack for shrinking
 	// is guaranteed to observe activeStackChans after this store.
-	atomic.Store8(&gp.parkingOnChan, 0)
+	gp.parkingOnChan.Store(false)
 	// Make sure we unlock after setting activeStackChans and
 	// unsetting parkingOnChan. The moment we unlock chanLock
 	// we risk gp getting readied by a channel operation and

src/runtime/runtime2.go

@@ -461,8 +461,8 @@ type g struct {
 	activeStackChans bool
 	// parkingOnChan indicates that the goroutine is about to
 	// park on a chansend or chanrecv. Used to signal an unsafe point
-	// for stack shrinking. It's a boolean value, but is updated atomically.
-	parkingOnChan uint8
+	// for stack shrinking.
+	parkingOnChan atomic.Bool
 
 	raceignore     int8     // ignore race detection events
 	sysblocktraced bool     // StartTrace has emitted EvGoInSyscall about this goroutine

src/runtime/select.go

@@ -8,7 +8,6 @@ package runtime
 
 import (
 	"internal/abi"
-	"runtime/internal/atomic"
 	"unsafe"
 )
 
@@ -70,7 +69,7 @@ func selparkcommit(gp *g, _ unsafe.Pointer) bool {
 	// Mark that it's safe for stack shrinking to occur now,
 	// because any thread acquiring this G's stack for shrinking
 	// is guaranteed to observe activeStackChans after this store.
-	atomic.Store8(&gp.parkingOnChan, 0)
+	gp.parkingOnChan.Store(false)
 	// Make sure we unlock after setting activeStackChans and
 	// unsetting parkingOnChan. The moment we unlock any of the
 	// channel locks we risk gp getting readied by a channel operation
@@ -324,7 +323,7 @@ func selectgo(cas0 *scase, order0 *uint16, pc0 *uintptr, nsends, nrecvs int, blo
 	// to park on a channel. The window between when this G's status
 	// changes and when we set gp.activeStackChans is not safe for
 	// stack shrinking.
-	atomic.Store8(&gp.parkingOnChan, 1)
+	gp.parkingOnChan.Store(true)
 	gopark(selparkcommit, nil, waitReasonSelect, traceEvGoBlockSelect, 1)
 	gp.activeStackChans = false
 

src/runtime/stack.go

@@ -886,7 +886,7 @@ func copystack(gp *g, newsize uintptr) {
 	// Adjust sudogs, synchronizing with channel ops if necessary.
 	ncopy := used
 	if !gp.activeStackChans {
-		if newsize < old.hi-old.lo && atomic.Load8(&gp.parkingOnChan) != 0 {
+		if newsize < old.hi-old.lo && gp.parkingOnChan.Load() {
 			// It's not safe for someone to shrink this stack while we're actively
 			// parking on a channel, but it is safe to grow since we do that
 			// ourselves and explicitly don't want to synchronize with channels
@@ -1150,7 +1150,7 @@ func isShrinkStackSafe(gp *g) bool {
 	// We also can't *shrink* the stack in the window between the
 	// goroutine calling gopark to park on a channel and
 	// gp.activeStackChans being set.
-	return gp.syscallsp == 0 && !gp.asyncSafePoint && atomic.Load8(&gp.parkingOnChan) == 0
+	return gp.syscallsp == 0 && !gp.asyncSafePoint && !gp.parkingOnChan.Load()
 }
 
 // Maybe shrink the stack being used by gp.