Update to go1.23.4

VERSION

@@ -1,2 +1,2 @@
-go1.23.3
+go1.23.4
-time 2024-11-06T18:46:45Z
+time 2024-11-27T20:27:20Z

patches/0004-Add-back-LoadLibraryA-fallback.patch

@@ -1,6 +1,6 @@
-From ed249cf4dbfe31b9cea185100b74c38e5c6e3bd9 Mon Sep 17 00:00:00 2001
+From 3e1a3a3c96117fd4d655dd85d2e2c807e691104e Mon Sep 17 00:00:00 2001
 From: Vorapol Rinsatitnon <vorapol.r@pm.me>
-Date: Sat, 9 Nov 2024 18:54:55 +1100
+Date: Tue, 24 Dec 2024 19:31:25 +0700
 Subject: [PATCH] Add back LoadLibraryA fallback
 
 ---
@@ -14,7 +14,7 @@ Subject: [PATCH] Add back LoadLibraryA fallback
  7 files changed, 136 insertions(+), 7 deletions(-)
 
 diff --git a/src/runtime/export_windows_test.go b/src/runtime/export_windows_test.go
-index 4880e62a55..8bfff0bc93 100644
+index 4880e62..8bfff0b 100644
 --- a/src/runtime/export_windows_test.go
 +++ b/src/runtime/export_windows_test.go
 @@ -36,3 +36,7 @@ func NewContextStub() *ContextStub {
@@ -26,7 +26,7 @@ index 4880e62a55..8bfff0bc93 100644
 +	return useLoadLibraryEx, _LoadLibraryExW != nil, _AddDllDirectory != nil
 +}
 diff --git a/src/runtime/os_windows.go b/src/runtime/os_windows.go
-index 02735802d4..c76df9da22 100644
+index 0273580..c76df9d 100644
 --- a/src/runtime/os_windows.go
 +++ b/src/runtime/os_windows.go
 @@ -41,6 +41,7 @@ const (
@@ -139,7 +139,7 @@ index 02735802d4..c76df9da22 100644
  
  // osRelaxMinNS indicates that sysmon shouldn't osRelax if the next
 diff --git a/src/runtime/syscall_windows.go b/src/runtime/syscall_windows.go
-index 85b1b8c902..eb808feea5 100644
+index 85b1b8c..eb808fe 100644
 --- a/src/runtime/syscall_windows.go
 +++ b/src/runtime/syscall_windows.go
 @@ -413,10 +413,23 @@ func callbackWrap(a *callbackArgs) {
@@ -169,7 +169,7 @@ index 85b1b8c902..eb808feea5 100644
  		err = 0
  	}
 diff --git a/src/runtime/syscall_windows_test.go b/src/runtime/syscall_windows_test.go
-index 156cf3eb8e..2db5b61a9b 100644
+index 156cf3e..2db5b61 100644
 --- a/src/runtime/syscall_windows_test.go
 +++ b/src/runtime/syscall_windows_test.go
 @@ -1166,7 +1166,10 @@ uintptr_t cfunc(void) {
@@ -210,11 +210,11 @@ index 156cf3eb8e..2db5b61a9b 100644
  	modwinmm    = syscall.NewLazyDLL("winmm.dll")
  	modkernel32 = syscall.NewLazyDLL("kernel32.dll")
 diff --git a/src/syscall/dll_windows.go b/src/syscall/dll_windows.go
-index 81134cb0bd..b3554d349b 100644
+index a7873e6..bd82b51 100644
 --- a/src/syscall/dll_windows.go
 +++ b/src/syscall/dll_windows.go
-@@ -44,7 +44,7 @@ func Syscall18(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a
+@@ -45,7 +45,7 @@ func Syscall18(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a
- 
+ //go:noescape
  func SyscallN(trap uintptr, args ...uintptr) (r1, r2 uintptr, err Errno)
  func loadlibrary(filename *uint16) (handle uintptr, err Errno)
 -func loadsystemlibrary(filename *uint16) (handle uintptr, err Errno)
@@ -222,7 +222,7 @@ index 81134cb0bd..b3554d349b 100644
  func getprocaddress(handle uintptr, procname *uint8) (proc uintptr, err Errno)
  
  // A DLL implements access to a single DLL.
-@@ -53,6 +53,26 @@ type DLL struct {
+@@ -54,6 +54,26 @@ type DLL struct {
  	Handle Handle
  }
  
@@ -249,7 +249,7 @@ index 81134cb0bd..b3554d349b 100644
  // LoadDLL loads the named DLL file into memory.
  //
  // If name is not an absolute path and is not a known system DLL used by
-@@ -69,7 +89,11 @@ func LoadDLL(name string) (*DLL, error) {
+@@ -70,7 +90,11 @@ func LoadDLL(name string) (*DLL, error) {
  	var h uintptr
  	var e Errno
  	if sysdll.IsSystemDLL[name] {
@@ -263,7 +263,7 @@ index 81134cb0bd..b3554d349b 100644
  		h, e = loadlibrary(namep)
  	}
 diff --git a/src/syscall/security_windows.go b/src/syscall/security_windows.go
-index 4e988c418a..45b1908b71 100644
+index 4e988c4..45b1908 100644
 --- a/src/syscall/security_windows.go
 +++ b/src/syscall/security_windows.go
 @@ -290,6 +290,7 @@ type Tokenprimarygroup struct {
@@ -275,7 +275,7 @@ index 4e988c418a..45b1908b71 100644
  // An access token contains the security information for a logon session.
  // The system creates an access token when a user logs on, and every
 diff --git a/src/syscall/zsyscall_windows.go b/src/syscall/zsyscall_windows.go
-index d8d8594a55..28369e3b91 100644
+index d8d8594..28369e3 100644
 --- a/src/syscall/zsyscall_windows.go
 +++ b/src/syscall/zsyscall_windows.go
 @@ -128,6 +128,7 @@ var (
@@ -303,5 +303,5 @@ index d8d8594a55..28369e3b91 100644
  	Syscall(procGetSystemTimeAsFileTime.Addr(), 1, uintptr(unsafe.Pointer(time)), 0, 0)
  	return
 -- 
-2.47.0
+2.39.5
 

src/cmd/cgo/internal/testcarchive/carchive_test.go

@@ -33,7 +33,7 @@ import (
 	"unicode"
 )
 
-var globalSkip = func(t *testing.T) {}
+var globalSkip = func(t testing.TB) {}
 
 // Program to run.
 var bin []string
@@ -59,12 +59,12 @@ func TestMain(m *testing.M) {
 
 func testMain(m *testing.M) int {
 	if testing.Short() && os.Getenv("GO_BUILDER_NAME") == "" {
-		globalSkip = func(t *testing.T) { t.Skip("short mode and $GO_BUILDER_NAME not set") }
+		globalSkip = func(t testing.TB) { t.Skip("short mode and $GO_BUILDER_NAME not set") }
 		return m.Run()
 	}
 	if runtime.GOOS == "linux" {
 		if _, err := os.Stat("/etc/alpine-release"); err == nil {
-			globalSkip = func(t *testing.T) { t.Skip("skipping failing test on alpine - go.dev/issue/19938") }
+			globalSkip = func(t testing.TB) { t.Skip("skipping failing test on alpine - go.dev/issue/19938") }
 			return m.Run()
 		}
 	}
@@ -1291,8 +1291,8 @@ func TestPreemption(t *testing.T) {
 	}
 }
 
-// Issue 59294. Test calling Go function from C after using some
+// Issue 59294 and 68285. Test calling Go function from C after with
-// stack space.
+// various stack space.
 func TestDeepStack(t *testing.T) {
 	globalSkip(t)
 	testenv.MustHaveGoBuild(t)
@@ -1350,6 +1350,53 @@ func TestDeepStack(t *testing.T) {
 	}
 }
 
+func BenchmarkCgoCallbackMainThread(b *testing.B) {
+	// Benchmark for calling into Go fron C main thread.
+	// See issue #68587.
+	//
+	// It uses a subprocess, which is a C binary that calls
+	// Go on the main thread b.N times. There is some overhead
+	// for launching the subprocess. It is probably fine when
+	// b.N is large.
+
+	globalSkip(b)
+	testenv.MustHaveGoBuild(b)
+	testenv.MustHaveCGO(b)
+	testenv.MustHaveBuildMode(b, "c-archive")
+
+	if !testWork {
+		defer func() {
+			os.Remove("testp10" + exeSuffix)
+			os.Remove("libgo10.a")
+			os.Remove("libgo10.h")
+		}()
+	}
+
+	cmd := exec.Command("go", "build", "-buildmode=c-archive", "-o", "libgo10.a", "./libgo10")
+	out, err := cmd.CombinedOutput()
+	b.Logf("%v\n%s", cmd.Args, out)
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	ccArgs := append(cc, "-o", "testp10"+exeSuffix, "main10.c", "libgo10.a")
+	out, err = exec.Command(ccArgs[0], ccArgs[1:]...).CombinedOutput()
+	b.Logf("%v\n%s", ccArgs, out)
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	argv := cmdToRun("./testp10")
+	argv = append(argv, fmt.Sprint(b.N))
+	cmd = exec.Command(argv[0], argv[1:]...)
+
+	b.ResetTimer()
+	err = cmd.Run()
+	if err != nil {
+		b.Fatal(err)
+	}
+}
+
 func TestSharedObject(t *testing.T) {
 	// Test that we can put a Go c-archive into a C shared object.
 	globalSkip(t)

src/cmd/cgo/internal/testcarchive/testdata/libgo10/a.go

@@ -0,0 +1,12 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "C"
+
+//export GoF
+func GoF() {}
+
+func main() {}

src/cmd/cgo/internal/testcarchive/testdata/libgo9/a.go

@@ -6,9 +6,29 @@ package main
 
 import "runtime"
 
+// extern void callGoWithVariousStack(int);
 import "C"
 
 func main() {}
 
 //export GoF
-func GoF() { runtime.GC() }
+func GoF(p int32) {
+	runtime.GC()
+	if p != 0 {
+		panic("panic")
+	}
+}
+
+//export callGoWithVariousStackAndGoFrame
+func callGoWithVariousStackAndGoFrame(p int32) {
+	if p != 0 {
+		defer func() {
+			e := recover()
+			if e == nil {
+				panic("did not panic")
+			}
+			runtime.GC()
+		}()
+	}
+	C.callGoWithVariousStack(C.int(p));
+}

src/cmd/cgo/internal/testcarchive/testdata/main10.c

@@ -0,0 +1,22 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "libgo10.h"
+
+int main(int argc, char **argv) {
+	int n, i;
+
+	if (argc != 2) {
+		perror("wrong arg");
+		return 2;
+	}
+	n = atoi(argv[1]);
+	for (i = 0; i < n; i++)
+		GoF();
+
+	return 0;
+}

src/cmd/cgo/internal/testcarchive/testdata/main9.c

@@ -6,19 +6,27 @@
 
 void use(int *x) { (*x)++; }
 
-void callGoFWithDeepStack() {
+void callGoFWithDeepStack(int p) {
 	int x[10000];
 
 	use(&x[0]);
 	use(&x[9999]);
 
-	GoF();
+	GoF(p);
 
 	use(&x[0]);
 	use(&x[9999]);
 }
 
-int main() {
+void callGoWithVariousStack(int p) {
-	GoF();                  // call GoF without using much stack
+	GoF(0);                  // call GoF without using much stack
-	callGoFWithDeepStack(); // call GoF with a deep stack
+	callGoFWithDeepStack(p); // call GoF with a deep stack
+	GoF(0);                  // again on a shallow stack
+}
+
+int main() {
+	callGoWithVariousStack(0);
+
+	callGoWithVariousStackAndGoFrame(0); // normal execution
+	callGoWithVariousStackAndGoFrame(1); // panic and recover
 }

src/cmd/compile/internal/escape/solve.go

@@ -318,9 +318,10 @@ func containsClosure(f, c *ir.Func) bool {
 		return false
 	}
 
-	// Closures within function Foo are named like "Foo.funcN..." or "Foo-rangeN".
+	for p := c.ClosureParent; p != nil; p = p.ClosureParent {
-	// TODO(mdempsky): Better way to recognize this.
+		if p == f {
-	fn := f.Sym().Name
+			return true
-	cn := c.Sym().Name
+		}
-	return len(cn) > len(fn) && cn[:len(fn)] == fn && (cn[len(fn)] == '.' || cn[len(fn)] == '-')
+	}
+	return false
 }

src/cmd/compile/internal/importer/gcimporter_test.go

@@ -582,6 +582,23 @@ func TestIssue25596(t *testing.T) {
 	compileAndImportPkg(t, "issue25596")
 }
 
+func TestIssue70394(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	pkg := compileAndImportPkg(t, "alias")
+	obj := lookupObj(t, pkg.Scope(), "A")
+
+	typ := obj.Type()
+	if _, ok := typ.(*types2.Alias); !ok {
+		t.Fatalf("type of %s is %s, wanted an alias", obj, typ)
+	}
+}
+
 func importPkg(t *testing.T, path, srcDir string) *types2.Package {
 	pkg, err := Import(make(map[string]*types2.Package), path, srcDir, nil)
 	if err != nil {

src/cmd/compile/internal/importer/testdata/alias.go

@@ -0,0 +1,7 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testdata
+
+type A = int32

src/cmd/compile/internal/importer/ureader.go

@@ -31,9 +31,7 @@ func ReadPackage(ctxt *types2.Context, imports map[string]*types2.Package, input
 
 		ctxt:        ctxt,
 		imports:     imports,
-		// Currently, the compiler panics when using Alias types.
+		enableAlias: true,
-		// TODO(gri) set to true once this is fixed (issue #66873)
-		enableAlias: false,
 
 		posBases: make([]*syntax.PosBase, input.NumElems(pkgbits.RelocPosBase)),
 		pkgs:     make([]*types2.Package, input.NumElems(pkgbits.RelocPkg)),

src/cmd/compile/internal/ir/func.go

@@ -51,6 +51,8 @@ import (
 // the generated ODCLFUNC, but there is no
 // pointer from the Func back to the OMETHVALUE.
 type Func struct {
+	// if you add or remove a field, don't forget to update sizeof_test.go
+
 	miniNode
 	Body Nodes
 
@@ -76,6 +78,9 @@ type Func struct {
 	// Populated during walk.
 	Closures []*Func
 
+	// Parent of a closure
+	ClosureParent *Func
+
 	// Parents records the parent scope of each scope within a
 	// function. The root scope (0) has no parent, so the i'th
 	// scope's parent is stored at Parents[i-1].
@@ -512,6 +517,7 @@ func NewClosureFunc(fpos, cpos src.XPos, why Op, typ *types.Type, outerfn *Func,
 
 	fn.Nname.Defn = fn
 	pkg.Funcs = append(pkg.Funcs, fn)
+	fn.ClosureParent = outerfn
 
 	return fn
 }

src/cmd/compile/internal/ir/sizeof_test.go

@@ -20,7 +20,7 @@ func TestSizeof(t *testing.T) {
 		_32bit uintptr     // size on 32bit platforms
 		_64bit uintptr     // size on 64bit platforms
 	}{
-		{Func{}, 176, 296},
+		{Func{}, 180, 304},
 		{Name{}, 96, 168},
 	}
 

src/cmd/compile/internal/rangefunc/rangefunc_test.go

@@ -2099,3 +2099,27 @@ func TestTwoLevelReturnCheck(t *testing.T) {
 		t.Errorf("Expected y=3, got y=%d\n", y)
 	}
 }
+
+func Bug70035(s1, s2, s3 []string) string {
+	var c1 string
+	for v1 := range slices.Values(s1) {
+		var c2 string
+		for v2 := range slices.Values(s2) {
+			var c3 string
+			for v3 := range slices.Values(s3) {
+				c3 = c3 + v3
+			}
+			c2 = c2 + v2 + c3
+		}
+		c1 = c1 + v1 + c2
+	}
+	return c1
+}
+
+func Test70035(t *testing.T) {
+	got := Bug70035([]string{"1", "2", "3"}, []string{"a", "b", "c"}, []string{"A", "B", "C"})
+	want := "1aABCbABCcABC2aABCbABCcABC3aABCbABCcABC"
+	if got != want {
+		t.Errorf("got %v, want %v", got, want)
+	}
+}

src/cmd/trace/gstate.go

@@ -257,6 +257,10 @@ func (gs *gState[R]) stop(ts trace.Time, stack trace.Stack, ctx *traceContext) {
 	if gs.lastStopStack != trace.NoStack {
 		stk = ctx.Stack(viewerFrames(gs.lastStopStack))
 	}
+	var endStk int
+	if stack != trace.NoStack {
+		endStk = ctx.Stack(viewerFrames(stack))
+	}
 	// Check invariants.
 	if gs.startRunningTime == 0 {
 		panic("silently broken trace or generator invariant (startRunningTime != 0) not held")
@@ -270,6 +274,7 @@ func (gs *gState[R]) stop(ts trace.Time, stack trace.Stack, ctx *traceContext) {
 		Dur:      ts.Sub(gs.startRunningTime),
 		Resource: uint64(gs.executing),
 		Stack:    stk,
+		EndStack: endStk,
 	})
 
 	// Flush completed ranges.

src/internal/poll/sendfile_bsd.go

@@ -72,6 +72,6 @@ func SendFile(dstFD *FD, src int, pos, remain int64) (written int64, err error,
 	if err == syscall.EAGAIN {
 		err = nil
 	}
-	handled = written != 0 || (err != syscall.ENOSYS && err != syscall.EINVAL)
+	handled = written != 0 || (err != syscall.ENOSYS && err != syscall.EINVAL && err != syscall.EOPNOTSUPP && err != syscall.ENOTSUP)
 	return
 }

src/net/sendfile_unix_alt.go

@@ -53,6 +53,9 @@ func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
 		if err != nil {
 			return 0, err, false
 		}
+		if fi.Mode()&(fs.ModeSymlink|fs.ModeDevice|fs.ModeCharDevice|fs.ModeIrregular) != 0 {
+			return 0, nil, false
+		}
 
 		remain = fi.Size()
 	}

src/net/sendfile_unix_test.go

@@ -0,0 +1,86 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix
+
+package net
+
+import (
+	"internal/testpty"
+	"io"
+	"os"
+	"sync"
+	"syscall"
+	"testing"
+)
+
+// Issue 70763: test that we don't fail on sendfile from a tty.
+func TestCopyFromTTY(t *testing.T) {
+	pty, ttyName, err := testpty.Open()
+	if err != nil {
+		t.Skipf("skipping test because pty open failed: %v", err)
+	}
+	defer pty.Close()
+
+	// Use syscall.Open so that the tty is blocking.
+	ttyFD, err := syscall.Open(ttyName, syscall.O_RDWR, 0)
+	if err != nil {
+		t.Skipf("skipping test because tty open failed: %v", err)
+	}
+	defer syscall.Close(ttyFD)
+
+	tty := os.NewFile(uintptr(ttyFD), "tty")
+	defer tty.Close()
+
+	ln := newLocalListener(t, "tcp")
+	defer ln.Close()
+
+	ch := make(chan bool)
+
+	const data = "data\n"
+
+	var wg sync.WaitGroup
+	defer wg.Wait()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		conn, err := ln.Accept()
+		if err != nil {
+			t.Error(err)
+			return
+		}
+		defer conn.Close()
+
+		buf := make([]byte, len(data))
+		if _, err := io.ReadFull(conn, buf); err != nil {
+			t.Error(err)
+		}
+
+		ch <- true
+	}()
+
+	conn, err := Dial("tcp", ln.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer conn.Close()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		if _, err := pty.Write([]byte(data)); err != nil {
+			t.Error(err)
+		}
+		<-ch
+		if err := pty.Close(); err != nil {
+			t.Error(err)
+		}
+	}()
+
+	lr := io.LimitReader(tty, int64(len(data)))
+	if _, err := io.Copy(conn, lr); err != nil {
+		t.Error(err)
+	}
+}

src/runtime/cgo/gcc_stack_unix.c

@@ -31,10 +31,11 @@ x_cgo_getstackbound(uintptr bounds[2])
 	pthread_attr_get_np(pthread_self(), &attr);
 	pthread_attr_getstack(&attr, &addr, &size); // low address
 #else
-	// We don't know how to get the current stacks, so assume they are the
+	// We don't know how to get the current stacks, leave it as
-	// same as the default stack bounds.
+	// 0 and the caller will use an estimate based on the current
-	pthread_attr_getstacksize(&attr, &size);
+	// SP.
-	addr = __builtin_frame_address(0) + 4096 - size;
+	addr = 0;
+	size = 0;
 #endif
 	pthread_attr_destroy(&attr);
 

src/runtime/cgocall.go

@@ -231,34 +231,6 @@ func cgocall(fn, arg unsafe.Pointer) int32 {
 func callbackUpdateSystemStack(mp *m, sp uintptr, signal bool) {
 	g0 := mp.g0
 
-	inBound := sp > g0.stack.lo && sp <= g0.stack.hi
-	if mp.ncgo > 0 && !inBound {
-		// ncgo > 0 indicates that this M was in Go further up the stack
-		// (it called C and is now receiving a callback).
-		//
-		// !inBound indicates that we were called with SP outside the
-		// expected system stack bounds (C changed the stack out from
-		// under us between the cgocall and cgocallback?).
-		//
-		// It is not safe for the C call to change the stack out from
-		// under us, so throw.
-
-		// Note that this case isn't possible for signal == true, as
-		// that is always passing a new M from needm.
-
-		// Stack is bogus, but reset the bounds anyway so we can print.
-		hi := g0.stack.hi
-		lo := g0.stack.lo
-		g0.stack.hi = sp + 1024
-		g0.stack.lo = sp - 32*1024
-		g0.stackguard0 = g0.stack.lo + stackGuard
-		g0.stackguard1 = g0.stackguard0
-
-		print("M ", mp.id, " procid ", mp.procid, " runtime: cgocallback with sp=", hex(sp), " out of bounds [", hex(lo), ", ", hex(hi), "]")
-		print("\n")
-		exit(2)
-	}
-
 	if !mp.isextra {
 		// We allocated the stack for standard Ms. Don't replace the
 		// stack bounds with estimated ones when we already initialized
@@ -266,26 +238,37 @@ func callbackUpdateSystemStack(mp *m, sp uintptr, signal bool) {
 		return
 	}
 
-	// This M does not have Go further up the stack. However, it may have
+	inBound := sp > g0.stack.lo && sp <= g0.stack.hi
-	// previously called into Go, initializing the stack bounds. Between
+	if inBound && mp.g0StackAccurate {
-	// that call returning and now the stack may have changed (perhaps the
+		// This M has called into Go before and has the stack bounds
-	// C thread is running a coroutine library). We need to update the
+		// initialized. We have the accurate stack bounds, and the SP
-	// stack bounds for this case.
+		// is in bounds. We expect it continues to run within the same
+		// bounds.
+		return
+	}
+
+	// We don't have an accurate stack bounds (either it never calls
+	// into Go before, or we couldn't get the accurate bounds), or the
+	// current SP is not within the previous bounds (the stack may have
+	// changed between calls). We need to update the stack bounds.
 	//
 	// N.B. we need to update the stack bounds even if SP appears to
-	// already be in bounds. Our "bounds" may actually be estimated dummy
+	// already be in bounds, if our bounds are estimated dummy bounds
-	// bounds (below). The actual stack bounds could have shifted but still
+	// (below). We may be in a different region within the same actual
-	// have partial overlap with our dummy bounds. If we failed to update
+	// stack bounds, but our estimates were not accurate. Or the actual
-	// in that case, we could find ourselves seemingly called near the
+	// stack bounds could have shifted but still have partial overlap with
-	// bottom of the stack bounds, where we quickly run out of space.
+	// our dummy bounds. If we failed to update in that case, we could find
+	// ourselves seemingly called near the bottom of the stack bounds, where
+	// we quickly run out of space.
 
 	// Set the stack bounds to match the current stack. If we don't
 	// actually know how big the stack is, like we don't know how big any
 	// scheduling stack is, but we assume there's at least 32 kB. If we
 	// can get a more accurate stack bound from pthread, use that, provided
-	// it actually contains SP..
+	// it actually contains SP.
 	g0.stack.hi = sp + 1024
 	g0.stack.lo = sp - 32*1024
+	mp.g0StackAccurate = false
 	if !signal && _cgo_getstackbound != nil {
 		// Don't adjust if called from the signal handler.
 		// We are on the signal stack, not the pthread stack.
@@ -296,12 +279,16 @@ func callbackUpdateSystemStack(mp *m, sp uintptr, signal bool) {
 		asmcgocall(_cgo_getstackbound, unsafe.Pointer(&bounds))
 		// getstackbound is an unsupported no-op on Windows.
 		//
+		// On Unix systems, if the API to get accurate stack bounds is
+		// not available, it returns zeros.
+		//
 		// Don't use these bounds if they don't contain SP. Perhaps we
 		// were called by something not using the standard thread
 		// stack.
 		if bounds[0] != 0 && sp > bounds[0] && sp <= bounds[1] {
 			g0.stack.lo = bounds[0]
 			g0.stack.hi = bounds[1]
+			mp.g0StackAccurate = true
 		}
 	}
 	g0.stackguard0 = g0.stack.lo + stackGuard
@@ -319,6 +306,8 @@ func cgocallbackg(fn, frame unsafe.Pointer, ctxt uintptr) {
 	}
 
 	sp := gp.m.g0.sched.sp // system sp saved by cgocallback.
+	oldStack := gp.m.g0.stack
+	oldAccurate := gp.m.g0StackAccurate
 	callbackUpdateSystemStack(gp.m, sp, false)
 
 	// The call from C is on gp.m's g0 stack, so we must ensure
@@ -380,6 +369,12 @@ func cgocallbackg(fn, frame unsafe.Pointer, ctxt uintptr) {
 	reentersyscall(savedpc, uintptr(savedsp), uintptr(savedbp))
 
 	gp.m.winsyscall = winsyscall
+
+	// Restore the old g0 stack bounds
+	gp.m.g0.stack = oldStack
+	gp.m.g0.stackguard0 = oldStack.lo + stackGuard
+	gp.m.g0.stackguard1 = gp.m.g0.stackguard0
+	gp.m.g0StackAccurate = oldAccurate
 }
 
 func cgocallbackg1(fn, frame unsafe.Pointer, ctxt uintptr) {

src/runtime/export_test.go

@@ -1886,3 +1886,30 @@ func (m *TraceMap) PutString(s string) (uint64, bool) {
 func (m *TraceMap) Reset() {
 	m.traceMap.reset()
 }
+
+func SetSpinInGCMarkDone(spin bool) {
+	gcDebugMarkDone.spinAfterRaggedBarrier.Store(spin)
+}
+
+func GCMarkDoneRestarted() bool {
+	// Only read this outside of the GC. If we're running during a GC, just report false.
+	mp := acquirem()
+	if gcphase != _GCoff {
+		releasem(mp)
+		return false
+	}
+	restarted := gcDebugMarkDone.restartedDueTo27993
+	releasem(mp)
+	return restarted
+}
+
+func GCMarkDoneResetRestartFlag() {
+	mp := acquirem()
+	for gcphase != _GCoff {
+		releasem(mp)
+		Gosched()
+		mp = acquirem()
+	}
+	gcDebugMarkDone.restartedDueTo27993 = false
+	releasem(mp)
+}

src/runtime/gc_test.go

@@ -6,6 +6,8 @@ package runtime_test
 
 import (
 	"fmt"
+	"internal/testenv"
+	"internal/weak"
 	"math/bits"
 	"math/rand"
 	"os"
@@ -787,3 +789,78 @@ func TestMemoryLimitNoGCPercent(t *testing.T) {
 func TestMyGenericFunc(t *testing.T) {
 	runtime.MyGenericFunc[int]()
 }
+
+func TestWeakToStrongMarkTermination(t *testing.T) {
+	testenv.MustHaveParallelism(t)
+
+	type T struct {
+		a *int
+		b int
+	}
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
+	defer debug.SetGCPercent(debug.SetGCPercent(-1))
+	w := make([]weak.Pointer[T], 2048)
+
+	// Make sure there's no out-standing GC from a previous test.
+	runtime.GC()
+
+	// Create many objects with a weak pointers to them.
+	for i := range w {
+		x := new(T)
+		x.a = new(int)
+		w[i] = weak.Make(x)
+	}
+
+	// Reset the restart flag.
+	runtime.GCMarkDoneResetRestartFlag()
+
+	// Prevent mark termination from completing.
+	runtime.SetSpinInGCMarkDone(true)
+
+	// Start a GC, and wait a little bit to get something spinning in mark termination.
+	// Simultaneously, fire off another goroutine to disable spinning. If everything's
+	// working correctly, then weak.Strong will block, so we need to make sure something
+	// prevents the GC from continuing to spin.
+	done := make(chan struct{})
+	go func() {
+		runtime.GC()
+		done <- struct{}{}
+	}()
+	go func() {
+		time.Sleep(100 * time.Millisecond)
+
+		// Let mark termination continue.
+		runtime.SetSpinInGCMarkDone(false)
+	}()
+	time.Sleep(10 * time.Millisecond)
+
+	// Perform many weak->strong conversions in the critical window.
+	var wg sync.WaitGroup
+	for _, wp := range w {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			wp.Strong()
+		}()
+	}
+
+	// Make sure the GC completes.
+	<-done
+
+	// Make sure all the weak->strong conversions finish.
+	wg.Wait()
+
+	// The bug is triggered if there's still mark work after gcMarkDone stops the world.
+	//
+	// This can manifest in one of two ways today:
+	// - An exceedingly rare crash in mark termination.
+	// - gcMarkDone restarts, as if issue #27993 is at play.
+	//
+	// Check for the latter. This is a fairly controlled environment, so #27993 is very
+	// unlikely to happen (it's already rare to begin with) but we'll always _appear_ to
+	// trigger the same bug if weak->strong conversions aren't properly coordinated with
+	// mark termination.
+	if runtime.GCMarkDoneRestarted() {
+		t.Errorf("gcMarkDone restarted")
+	}
+}

src/runtime/lockrank.go

@@ -17,6 +17,7 @@ const (
 	lockRankDefer
 	lockRankSweepWaiters
 	lockRankAssistQueue
+	lockRankStrongFromWeakQueue
 	lockRankSweep
 	lockRankTestR
 	lockRankTestW
@@ -90,6 +91,7 @@ var lockNames = []string{
 	lockRankDefer:               "defer",
 	lockRankSweepWaiters:        "sweepWaiters",
 	lockRankAssistQueue:         "assistQueue",
+	lockRankStrongFromWeakQueue: "strongFromWeakQueue",
 	lockRankSweep:               "sweep",
 	lockRankTestR:               "testR",
 	lockRankTestW:               "testW",
@@ -169,6 +171,7 @@ var lockPartialOrder [][]lockRank = [][]lockRank{
 	lockRankDefer:               {},
 	lockRankSweepWaiters:        {},
 	lockRankAssistQueue:         {},
+	lockRankStrongFromWeakQueue: {},
 	lockRankSweep:               {},
 	lockRankTestR:               {},
 	lockRankTestW:               {},
@@ -180,11 +183,11 @@ var lockPartialOrder [][]lockRank = [][]lockRank{
 	lockRankPollDesc:            {},
 	lockRankWakeableSleep:       {},
 	lockRankHchan:               {lockRankSysmon, lockRankScavenge, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankWakeableSleep, lockRankHchan},
-	lockRankAllocmR:         {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan},
+	lockRankAllocmR:             {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan},
-	lockRankExecR:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan},
+	lockRankExecR:               {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan},
-	lockRankSched:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR},
+	lockRankSched:               {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR},
-	lockRankAllg:            {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched},
+	lockRankAllg:                {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched},
-	lockRankAllp:            {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched},
+	lockRankAllp:                {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched},
 	lockRankNotifyList:          {},
 	lockRankSudog:               {lockRankSysmon, lockRankScavenge, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankWakeableSleep, lockRankHchan, lockRankNotifyList},
 	lockRankTimers:              {lockRankSysmon, lockRankScavenge, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankTimers},
@@ -196,29 +199,29 @@ var lockPartialOrder [][]lockRank = [][]lockRank{
 	lockRankUserArenaState:      {},
 	lockRankTraceBuf:            {lockRankSysmon, lockRankScavenge},
 	lockRankTraceStrings:        {lockRankSysmon, lockRankScavenge, lockRankTraceBuf},
-	lockRankFin:             {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
+	lockRankFin:                 {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
-	lockRankSpanSetSpine:    {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
+	lockRankSpanSetSpine:        {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
-	lockRankMspanSpecial:    {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
+	lockRankMspanSpecial:        {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
-	lockRankTraceTypeTab:    {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
+	lockRankTraceTypeTab:        {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
-	lockRankGcBitsArenas:    {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankMspanSpecial},
+	lockRankGcBitsArenas:        {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankMspanSpecial},
-	lockRankProfInsert:      {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
+	lockRankProfInsert:          {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
-	lockRankProfBlock:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
+	lockRankProfBlock:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
-	lockRankProfMemActive:   {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
+	lockRankProfMemActive:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
-	lockRankProfMemFuture:   {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankProfMemActive},
+	lockRankProfMemFuture:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankProfMemActive},
-	lockRankGscan:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture},
+	lockRankGscan:               {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture},
-	lockRankStackpool:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan},
+	lockRankStackpool:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan},
-	lockRankStackLarge:      {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan},
+	lockRankStackLarge:          {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan},
-	lockRankHchanLeaf:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankHchanLeaf},
+	lockRankHchanLeaf:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankHchanLeaf},
-	lockRankWbufSpans:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan},
+	lockRankWbufSpans:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan},
-	lockRankMheap:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans},
+	lockRankMheap:               {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans},
-	lockRankMheapSpecial:    {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap},
+	lockRankMheapSpecial:        {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap},
-	lockRankGlobalAlloc:     {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap, lockRankMheapSpecial},
+	lockRankGlobalAlloc:         {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap, lockRankMheapSpecial},
-	lockRankTrace:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap},
+	lockRankTrace:               {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap},
-	lockRankTraceStackTab:   {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap, lockRankTrace},
+	lockRankTraceStackTab:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap, lockRankTrace},
 	lockRankPanic:               {},
 	lockRankDeadlock:            {lockRankPanic, lockRankDeadlock},
 	lockRankRaceFini:            {lockRankPanic},
-	lockRankAllocmRInternal: {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankAllocmW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR},
+	lockRankAllocmRInternal:     {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankAllocmW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR},
-	lockRankExecRInternal:   {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankExecR},
+	lockRankExecRInternal:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankExecR},
 	lockRankTestRInternal:       {lockRankTestR, lockRankTestW},
 }

src/runtime/mgc.go

@@ -190,6 +190,7 @@ func gcinit() {
 	work.markDoneSema = 1
 	lockInit(&work.sweepWaiters.lock, lockRankSweepWaiters)
 	lockInit(&work.assistQueue.lock, lockRankAssistQueue)
+	lockInit(&work.strongFromWeak.lock, lockRankStrongFromWeakQueue)
 	lockInit(&work.wbufSpans.lock, lockRankWbufSpans)
 }
 
@@ -418,6 +419,26 @@ type workType struct {
 		list gList
 	}
 
+	// strongFromWeak controls how the GC interacts with weak->strong
+	// pointer conversions.
+	strongFromWeak struct {
+		// block is a flag set during mark termination that prevents
+		// new weak->strong conversions from executing by blocking the
+		// goroutine and enqueuing it onto q.
+		//
+		// Mutated only by one goroutine at a time in gcMarkDone,
+		// with globally-synchronizing events like forEachP and
+		// stopTheWorld.
+		block bool
+
+		// q is a queue of goroutines that attempted to perform a
+		// weak->strong conversion during mark termination.
+		//
+		// Protected by lock.
+		lock mutex
+		q    gQueue
+	}
+
 	// cycles is the number of completed GC cycles, where a GC
 	// cycle is sweep termination, mark, mark termination, and
 	// sweep. This differs from memstats.numgc, which is
@@ -800,6 +821,19 @@ func gcStart(trigger gcTrigger) {
 // This is protected by markDoneSema.
 var gcMarkDoneFlushed uint32
 
+// gcDebugMarkDone contains fields used to debug/test mark termination.
+var gcDebugMarkDone struct {
+	// spinAfterRaggedBarrier forces gcMarkDone to spin after it executes
+	// the ragged barrier.
+	spinAfterRaggedBarrier atomic.Bool
+
+	// restartedDueTo27993 indicates that we restarted mark termination
+	// due to the bug described in issue #27993.
+	//
+	// Protected by worldsema.
+	restartedDueTo27993 bool
+}
+
 // gcMarkDone transitions the GC from mark to mark termination if all
 // reachable objects have been marked (that is, there are no grey
 // objects and can be no more in the future). Otherwise, it flushes
@@ -842,6 +876,10 @@ top:
 	// stop the world later, so acquire worldsema now.
 	semacquire(&worldsema)
 
+	// Prevent weak->strong conversions from generating additional
+	// GC work. forEachP will guarantee that it is observed globally.
+	work.strongFromWeak.block = true
+
 	// Flush all local buffers and collect flushedWork flags.
 	gcMarkDoneFlushed = 0
 	forEachP(waitReasonGCMarkTermination, func(pp *p) {
@@ -872,6 +910,10 @@ top:
 		goto top
 	}
 
+	// For debugging/testing.
+	for gcDebugMarkDone.spinAfterRaggedBarrier.Load() {
+	}
+
 	// There was no global work, no local work, and no Ps
 	// communicated work since we took markDoneSema. Therefore
 	// there are no grey objects and no more objects can be
@@ -910,6 +952,8 @@ top:
 		}
 	})
 	if restart {
+		gcDebugMarkDone.restartedDueTo27993 = true
+
 		getg().m.preemptoff = ""
 		systemstack(func() {
 			// Accumulate the time we were stopped before we had to start again.
@@ -936,6 +980,11 @@ top:
 	// start the world again.
 	gcWakeAllAssists()
 
+	// Wake all blocked weak->strong conversions. These will run
+	// when we start the world again.
+	work.strongFromWeak.block = false
+	gcWakeAllStrongFromWeak()
+
 	// Likewise, release the transition lock. Blocked
 	// workers and assists will run when we start the
 	// world again.

src/runtime/mheap.go

@@ -2049,8 +2049,19 @@ func internal_weak_runtime_registerWeakPointer(p unsafe.Pointer) unsafe.Pointer
 func internal_weak_runtime_makeStrongFromWeak(u unsafe.Pointer) unsafe.Pointer {
 	handle := (*atomic.Uintptr)(u)
 
-	// Prevent preemption. We want to make sure that another GC cycle can't start.
+	// Prevent preemption. We want to make sure that another GC cycle can't start
+	// and that work.strongFromWeak.block can't change out from under us.
 	mp := acquirem()
+
+	// Yield to the GC if necessary.
+	if work.strongFromWeak.block {
+		releasem(mp)
+
+		// Try to park and wait for mark termination.
+		// N.B. gcParkStrongFromWeak calls acquirem before returning.
+		mp = gcParkStrongFromWeak()
+	}
+
 	p := handle.Load()
 	if p == 0 {
 		releasem(mp)
@@ -2092,6 +2103,41 @@ func internal_weak_runtime_makeStrongFromWeak(u unsafe.Pointer) unsafe.Pointer {
 	return ptr
 }
 
+// gcParkStrongFromWeak puts the current goroutine on the weak->strong queue and parks.
+func gcParkStrongFromWeak() *m {
+	// Prevent preemption as we check strongFromWeak, so it can't change out from under us.
+	mp := acquirem()
+
+	for work.strongFromWeak.block {
+		lock(&work.strongFromWeak.lock)
+		releasem(mp) // N.B. Holding the lock prevents preemption.
+
+		// Queue ourselves up.
+		work.strongFromWeak.q.pushBack(getg())
+
+		// Park.
+		goparkunlock(&work.strongFromWeak.lock, waitReasonGCWeakToStrongWait, traceBlockGCWeakToStrongWait, 2)
+
+		// Re-acquire the current M since we're going to check the condition again.
+		mp = acquirem()
+
+		// Re-check condition. We may have awoken in the next GC's mark termination phase.
+	}
+	return mp
+}
+
+// gcWakeAllStrongFromWeak wakes all currently blocked weak->strong
+// conversions. This is used at the end of a GC cycle.
+//
+// work.strongFromWeak.block must be false to prevent woken goroutines
+// from immediately going back to sleep.
+func gcWakeAllStrongFromWeak() {
+	lock(&work.strongFromWeak.lock)
+	list := work.strongFromWeak.q.popList()
+	injectglist(&list)
+	unlock(&work.strongFromWeak.lock)
+}
+
 // Retrieves or creates a weak pointer handle for the object p.
 func getOrAddWeakHandle(p unsafe.Pointer) *atomic.Uintptr {
 	// First try to retrieve without allocating.
@@ -2126,8 +2172,14 @@ func getOrAddWeakHandle(p unsafe.Pointer) *atomic.Uintptr {
 
 		// Keep p alive for the duration of the function to ensure
 		// that it cannot die while we're trying to do this.
+		//
+		// Same for handle, which is only stored in the special.
+		// There's a window where it might die if we don't keep it
+		// alive explicitly. Returning it here is probably good enough,
+		// but let's be defensive and explicit. See #70455.
 		KeepAlive(p)
-		return s.handle
+		KeepAlive(handle)
+		return handle
 	}
 
 	// There was an existing handle. Free the special
@@ -2147,7 +2199,10 @@ func getOrAddWeakHandle(p unsafe.Pointer) *atomic.Uintptr {
 
 	// Keep p alive for the duration of the function to ensure
 	// that it cannot die while we're trying to do this.
+	//
+	// Same for handle, just to be defensive.
 	KeepAlive(p)
+	KeepAlive(handle)
 	return handle
 }
 

src/runtime/mklockrank.go

@@ -50,6 +50,7 @@ NONE < defer;
 NONE <
   sweepWaiters,
   assistQueue,
+  strongFromWeakQueue,
   sweep;
 
 # Test only
@@ -66,6 +67,7 @@ assistQueue,
   hchan,
   pollDesc, # pollDesc can interact with timers, which can lock sched.
   scavenge,
+  strongFromWeakQueue,
   sweep,
   sweepWaiters,
   testR,

src/runtime/proc.go

@@ -2539,6 +2539,7 @@ func dropm() {
 	g0.stack.lo = 0
 	g0.stackguard0 = 0
 	g0.stackguard1 = 0
+	mp.g0StackAccurate = false
 
 	putExtraM(mp)
 

src/runtime/runtime2.go

@@ -584,6 +584,7 @@ type m struct {
 	isExtraInSig    bool          // m is an extra m in a signal handler
 	freeWait        atomic.Uint32 // Whether it is safe to free g0 and delete m (one of freeMRef, freeMStack, freeMWait)
 	needextram      bool
+	g0StackAccurate bool // whether the g0 stack has accurate bounds
 	traceback       uint8
 	ncgocall        uint64        // number of cgo calls in total
 	ncgo            int32         // number of cgo calls currently in progress
@@ -1095,6 +1096,7 @@ const (
 	waitReasonTraceProcStatus                         // "trace proc status"
 	waitReasonPageTraceFlush                          // "page trace flush"
 	waitReasonCoroutine                               // "coroutine"
+	waitReasonGCWeakToStrongWait                      // "GC weak to strong wait"
 )
 
 var waitReasonStrings = [...]string{
@@ -1135,6 +1137,7 @@ var waitReasonStrings = [...]string{
 	waitReasonTraceProcStatus:       "trace proc status",
 	waitReasonPageTraceFlush:        "page trace flush",
 	waitReasonCoroutine:             "coroutine",
+	waitReasonGCWeakToStrongWait:    "GC weak to strong wait",
 }
 
 func (w waitReason) String() string {

src/runtime/stack.go

@@ -69,7 +69,7 @@ const (
 	// to each stack below the usual guard area for OS-specific
 	// purposes like signal handling. Used on Windows, Plan 9,
 	// and iOS because they do not use a separate stack.
-	stackSystem = goos.IsWindows*512*goarch.PtrSize + goos.IsPlan9*512 + goos.IsIos*goarch.IsArm64*1024
+	stackSystem = goos.IsWindows*4096 + goos.IsPlan9*512 + goos.IsIos*goarch.IsArm64*1024
 
 	// The minimum size of stack used by Go code
 	stackMin = 2048
@@ -1330,7 +1330,7 @@ func morestackc() {
 }
 
 // startingStackSize is the amount of stack that new goroutines start with.
-// It is a power of 2, and between _FixedStack and maxstacksize, inclusive.
+// It is a power of 2, and between fixedStack and maxstacksize, inclusive.
 // startingStackSize is updated every GC by tracking the average size of
 // stacks scanned during the GC.
 var startingStackSize uint32 = fixedStack

src/runtime/traceruntime.go

@@ -99,6 +99,7 @@ const (
 	traceBlockDebugCall
 	traceBlockUntilGCEnds
 	traceBlockSleep
+	traceBlockGCWeakToStrongWait
 )
 
 var traceBlockReasonStrings = [...]string{
@@ -117,6 +118,7 @@ var traceBlockReasonStrings = [...]string{
 	traceBlockDebugCall:          "wait for debug call",
 	traceBlockUntilGCEnds:        "wait until GC ends",
 	traceBlockSleep:              "sleep",
+	traceBlockGCWeakToStrongWait: "GC weak to strong wait",
 }
 
 // traceGoStopReason is an enumeration of reasons a goroutine might yield.

src/syscall/dll_windows.go

@@ -42,6 +42,7 @@ func Syscall15(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a
 // Deprecated: Use [SyscallN] instead.
 func Syscall18(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18 uintptr) (r1, r2 uintptr, err Errno)
 
+//go:noescape
 func SyscallN(trap uintptr, args ...uintptr) (r1, r2 uintptr, err Errno)
 func loadlibrary(filename *uint16) (handle uintptr, err Errno)
 func loadsystemlibrary(filename *uint16, absoluteFilepath *uint16) (handle uintptr, err Errno)

src/syscall/syscall_windows_test.go

@@ -213,6 +213,51 @@ func TestGetStartupInfo(t *testing.T) {
 	}
 }
 
+func TestSyscallAllocations(t *testing.T) {
+	testenv.SkipIfOptimizationOff(t)
+
+	// Test that syscall.SyscallN arguments do not escape.
+	// The function used (in this case GetVersion) doesn't matter
+	// as long as it is always available and doesn't panic.
+	h, err := syscall.LoadLibrary("kernel32.dll")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer syscall.FreeLibrary(h)
+	proc, err := syscall.GetProcAddress(h, "GetVersion")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	testAllocs := func(t *testing.T, name string, fn func() error) {
+		t.Run(name, func(t *testing.T) {
+			n := int(testing.AllocsPerRun(10, func() {
+				if err := fn(); err != nil {
+					t.Fatalf("%s: %v", name, err)
+				}
+			}))
+			if n > 0 {
+				t.Errorf("allocs = %d, want 0", n)
+			}
+		})
+	}
+
+	testAllocs(t, "SyscallN", func() error {
+		r0, _, e1 := syscall.SyscallN(proc, 0, 0, 0)
+		if r0 == 0 {
+			return syscall.Errno(e1)
+		}
+		return nil
+	})
+	testAllocs(t, "Syscall", func() error {
+		r0, _, e1 := syscall.Syscall(proc, 3, 0, 0, 0)
+		if r0 == 0 {
+			return syscall.Errno(e1)
+		}
+		return nil
+	})
+}
+
 func FuzzUTF16FromString(f *testing.F) {
 	f.Add("hi")           // ASCII
 	f.Add("â")            // latin1

src/time/time_test.go

@@ -14,6 +14,7 @@ import (
 	"math/rand"
 	"os"
 	"runtime"
+	"slices"
 	"strings"
 	"sync"
 	"testing"
@@ -1084,10 +1085,15 @@ func TestLoadFixed(t *testing.T) {
 	// So GMT+1 corresponds to -3600 in the Go zone, not +3600.
 	name, offset := Now().In(loc).Zone()
 	// The zone abbreviation is "-01" since tzdata-2016g, and "GMT+1"
-	// on earlier versions; we accept both. (Issue #17276).
+	// on earlier versions; we accept both. (Issue 17276.)
-	if !(name == "GMT+1" || name == "-01") || offset != -1*60*60 {
+	wantName := []string{"GMT+1", "-01"}
-		t.Errorf("Now().In(loc).Zone() = %q, %d, want %q or %q, %d",
+	// The zone abbreviation may be "+01" on OpenBSD. (Issue 69840.)
-			name, offset, "GMT+1", "-01", -1*60*60)
+	if runtime.GOOS == "openbsd" {
+		wantName = append(wantName, "+01")
+	}
+	if !slices.Contains(wantName, name) || offset != -1*60*60 {
+		t.Errorf("Now().In(loc).Zone() = %q, %d, want %q (one of), %d",
+			name, offset, wantName, -1*60*60)
 	}
 }