runtime: revert Apple libc atfork workaround

Revert CL 451735 (1f4394a0c9), which fixed #33565 and #56784
but also introduced #57263.

I have a different fix to apply instead. Since the first fix was
never backported, it will be easiest to backport the new fix
if the new fix is done in a separate CL from the revert.

Change-Id: I6c8ea3a46e542ee4702675bbc058e29ccd2723e0
Reviewed-on: https://go-review.googlesource.com/c/go/+/459175
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>

src/runtime/os_darwin.go

@@ -136,8 +136,6 @@ func osinit() {
 
 	ncpu = getncpu()
 	physPageSize = getPageSize()
-
-	osinit_hack()
 }
 
 func sysctlbynameInt32(name []byte) (int32, int32) {

src/runtime/sys_darwin.go

@@ -179,51 +179,6 @@ func pthread_kill(t pthread, sig uint32) {
 }
 func pthread_kill_trampoline()
 
-// osinit_hack is a clumsy hack to work around Apple libc bugs
-// causing fork+exec to hang in the child process intermittently.
-// See go.dev/issue/33565 and go.dev/issue/56784 for a few reports.
-//
-// The stacks obtained from the hung child processes are in
-// libSystem_atfork_child, which is supposed to reinitialize various
-// parts of the C library in the new process.
-//
-// One common stack dies in _notify_fork_child calling _notify_globals
-// (inlined) calling _os_alloc_once, because _os_alloc_once detects that
-// the once lock is held by the parent process and then calls
-// _os_once_gate_corruption_abort. The allocation is setting up the
-// globals for the notification subsystem. See the source code at [1].
-// To work around this, we can allocate the globals earlier in the Go
-// program's lifetime, before any execs are involved, by calling any
-// notify routine that is exported, calls _notify_globals, and doesn't do
-// anything too expensive otherwise. notify_is_valid_token(0) fits the bill.
-//
-// The other common stack dies in xpc_atfork_child calling
-// _objc_msgSend_uncached which ends up in
-// WAITING_FOR_ANOTHER_THREAD_TO_FINISH_CALLING_+initialize. Of course,
-// whatever thread the child is waiting for is in the parent process and
-// is not going to finish anything in the child process. There is no
-// public source code for these routines, so it is unclear exactly what
-// the problem is. However, xpc_atfork_child turns out to be exported
-// (for use by libSystem_atfork_child, which is in a different library,
-// so xpc_atfork_child is unlikely to be unexported any time soon).
-// It also stands to reason that since xpc_atfork_child is called at the
-// start of any forked child process, it can't be too harmful to call at
-// the start of an ordinary Go process. And whatever caches it needs for
-// a non-deadlocking fast path during exec empirically do get initialized
-// by calling it at startup.
-//
-// So osinit_hack_trampoline (in sys_darwin_$GOARCH.s) calls
-// notify_is_valid_token(0) and xpc_atfork_child(), which makes the
-// fork+exec hangs stop happening. If Apple fixes the libc bug in
-// some future version of macOS, then we can remove this awful code.
-//
-//go:nosplit
-func osinit_hack() {
-	libcCall(unsafe.Pointer(abi.FuncPCABI0(osinit_hack_trampoline)), nil)
-	return
-}
-func osinit_hack_trampoline()
-
 // mmap is used to do low-level memory allocation via mmap. Don't allow stack
 // splits, since this function (used by sysAlloc) is called in a lot of low-level
 // parts of the runtime and callers often assume it won't acquire any locks.
@@ -593,6 +548,3 @@ func setNonblock(fd int32) {
 //go:cgo_import_dynamic libc_pthread_cond_wait pthread_cond_wait "/usr/lib/libSystem.B.dylib"
 //go:cgo_import_dynamic libc_pthread_cond_timedwait_relative_np pthread_cond_timedwait_relative_np "/usr/lib/libSystem.B.dylib"
 //go:cgo_import_dynamic libc_pthread_cond_signal pthread_cond_signal "/usr/lib/libSystem.B.dylib"
-
-//go:cgo_import_dynamic libc_notify_is_valid_token notify_is_valid_token "/usr/lib/libSystem.B.dylib"
-//go:cgo_import_dynamic libc_xpc_atfork_child xpc_atfork_child "/usr/lib/libSystem.B.dylib"

src/runtime/sys_darwin_amd64.s

@@ -597,15 +597,6 @@ TEXT runtime·pthread_kill_trampoline(SB),NOSPLIT,$0
 	POPQ	BP
 	RET
 
-TEXT runtime·osinit_hack_trampoline(SB),NOSPLIT,$0
-	PUSHQ	BP
-	MOVQ	SP, BP
-	MOVQ	$0, DI	// arg 1 val
-	CALL	libc_notify_is_valid_token(SB)
-	CALL	libc_xpc_atfork_child(SB)
-	POPQ	BP
-	RET
-
 // syscall calls a function in libc on behalf of the syscall package.
 // syscall takes a pointer to a struct like:
 // struct {

src/runtime/sys_darwin_arm64.s

@@ -458,12 +458,6 @@ TEXT runtime·pthread_setspecific_trampoline(SB),NOSPLIT,$0
 	BL	libc_pthread_setspecific(SB)
 	RET
 
-TEXT runtime·osinit_hack_trampoline(SB),NOSPLIT,$0
-	MOVD	$0, R0	// arg 1 val
-	BL	libc_notify_is_valid_token(SB)
-	BL	libc_xpc_atfork_child(SB)
-	RET
-
 // syscall calls a function in libc on behalf of the syscall package.
 // syscall takes a pointer to a struct like:
 // struct {