runtime: use eventfd as the event wait/notify mechanism for epoll

Fixes #65443

Change-Id: I9ad4689b36e87ee930d35a38322a8797896483b4
Reviewed-on: https://go-review.googlesource.com/c/go/+/560615
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Jorropo <jorropo.pgm@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

src/runtime/internal/syscall/defs_linux.go

@@ -0,0 +1,9 @@
+// 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 syscall
+
+const (
+	EFD_CLOEXEC = 0x80000
+)

src/runtime/internal/syscall/defs_linux_386.go

@@ -10,6 +10,7 @@ const (
 	SYS_EPOLL_PWAIT   = 319
 	SYS_EPOLL_CREATE1 = 329
 	SYS_EPOLL_PWAIT2  = 441
+	SYS_EVENTFD2      = 328
 
 	EPOLLIN       = 0x1
 	EPOLLOUT      = 0x4
@@ -21,6 +22,7 @@ const (
 	EPOLL_CTL_ADD = 0x1
 	EPOLL_CTL_DEL = 0x2
 	EPOLL_CTL_MOD = 0x3
+	EFD_NONBLOCK  = 0x800
 )
 
 type EpollEvent struct {

src/runtime/internal/syscall/defs_linux_amd64.go

@@ -10,6 +10,7 @@ const (
 	SYS_EPOLL_PWAIT   = 281
 	SYS_EPOLL_CREATE1 = 291
 	SYS_EPOLL_PWAIT2  = 441
+	SYS_EVENTFD2      = 290
 
 	EPOLLIN       = 0x1
 	EPOLLOUT      = 0x4
@@ -21,6 +22,7 @@ const (
 	EPOLL_CTL_ADD = 0x1
 	EPOLL_CTL_DEL = 0x2
 	EPOLL_CTL_MOD = 0x3
+	EFD_NONBLOCK  = 0x800
 )
 
 type EpollEvent struct {

src/runtime/internal/syscall/defs_linux_arm.go

@@ -10,6 +10,7 @@ const (
 	SYS_EPOLL_PWAIT   = 346
 	SYS_EPOLL_CREATE1 = 357
 	SYS_EPOLL_PWAIT2  = 441
+	SYS_EVENTFD2      = 356
 
 	EPOLLIN       = 0x1
 	EPOLLOUT      = 0x4
@@ -21,6 +22,7 @@ const (
 	EPOLL_CTL_ADD = 0x1
 	EPOLL_CTL_DEL = 0x2
 	EPOLL_CTL_MOD = 0x3
+	EFD_NONBLOCK  = 0x800
 )
 
 type EpollEvent struct {

src/runtime/internal/syscall/defs_linux_arm64.go

@@ -10,6 +10,7 @@ const (
 	SYS_EPOLL_PWAIT   = 22
 	SYS_FCNTL         = 25
 	SYS_EPOLL_PWAIT2  = 441
+	SYS_EVENTFD2      = 19
 
 	EPOLLIN       = 0x1
 	EPOLLOUT      = 0x4
@@ -21,6 +22,7 @@ const (
 	EPOLL_CTL_ADD = 0x1
 	EPOLL_CTL_DEL = 0x2
 	EPOLL_CTL_MOD = 0x3
+	EFD_NONBLOCK  = 0x800
 )
 
 type EpollEvent struct {

src/runtime/internal/syscall/defs_linux_loong64.go

@@ -10,6 +10,7 @@ const (
 	SYS_EPOLL_PWAIT   = 22
 	SYS_FCNTL         = 25
 	SYS_EPOLL_PWAIT2  = 441
+	SYS_EVENTFD2      = 19
 
 	EPOLLIN       = 0x1
 	EPOLLOUT      = 0x4
@@ -21,6 +22,7 @@ const (
 	EPOLL_CTL_ADD = 0x1
 	EPOLL_CTL_DEL = 0x2
 	EPOLL_CTL_MOD = 0x3
+	EFD_NONBLOCK  = 0x800
 )
 
 type EpollEvent struct {

src/runtime/internal/syscall/defs_linux_mips64x.go

@@ -12,6 +12,7 @@ const (
 	SYS_EPOLL_PWAIT   = 5272
 	SYS_EPOLL_CREATE1 = 5285
 	SYS_EPOLL_PWAIT2  = 5441
+	SYS_EVENTFD2      = 5284
 
 	EPOLLIN       = 0x1
 	EPOLLOUT      = 0x4
@@ -23,6 +24,7 @@ const (
 	EPOLL_CTL_ADD = 0x1
 	EPOLL_CTL_DEL = 0x2
 	EPOLL_CTL_MOD = 0x3
+	EFD_NONBLOCK  = 0x80
 )
 
 type EpollEvent struct {

src/runtime/internal/syscall/defs_linux_mipsx.go

@@ -12,6 +12,7 @@ const (
 	SYS_EPOLL_PWAIT   = 4313
 	SYS_EPOLL_CREATE1 = 4326
 	SYS_EPOLL_PWAIT2  = 4441
+	SYS_EVENTFD2      = 4325
 
 	EPOLLIN       = 0x1
 	EPOLLOUT      = 0x4
@@ -23,6 +24,7 @@ const (
 	EPOLL_CTL_ADD = 0x1
 	EPOLL_CTL_DEL = 0x2
 	EPOLL_CTL_MOD = 0x3
+	EFD_NONBLOCK  = 0x80
 )
 
 type EpollEvent struct {

src/runtime/internal/syscall/defs_linux_ppc64x.go

@@ -12,6 +12,7 @@ const (
 	SYS_EPOLL_PWAIT   = 303
 	SYS_EPOLL_CREATE1 = 315
 	SYS_EPOLL_PWAIT2  = 441
+	SYS_EVENTFD2      = 314
 
 	EPOLLIN       = 0x1
 	EPOLLOUT      = 0x4
@@ -23,6 +24,7 @@ const (
 	EPOLL_CTL_ADD = 0x1
 	EPOLL_CTL_DEL = 0x2
 	EPOLL_CTL_MOD = 0x3
+	EFD_NONBLOCK  = 0x800
 )
 
 type EpollEvent struct {

src/runtime/internal/syscall/defs_linux_riscv64.go

@@ -10,6 +10,7 @@ const (
 	SYS_EPOLL_PWAIT   = 22
 	SYS_FCNTL         = 25
 	SYS_EPOLL_PWAIT2  = 441
+	SYS_EVENTFD2      = 19
 
 	EPOLLIN       = 0x1
 	EPOLLOUT      = 0x4
@@ -21,6 +22,7 @@ const (
 	EPOLL_CTL_ADD = 0x1
 	EPOLL_CTL_DEL = 0x2
 	EPOLL_CTL_MOD = 0x3
+	EFD_NONBLOCK  = 0x800
 )
 
 type EpollEvent struct {

src/runtime/internal/syscall/defs_linux_s390x.go

@@ -10,6 +10,7 @@ const (
 	SYS_EPOLL_PWAIT   = 312
 	SYS_EPOLL_CREATE1 = 327
 	SYS_EPOLL_PWAIT2  = 441
+	SYS_EVENTFD2      = 323
 
 	EPOLLIN       = 0x1
 	EPOLLOUT      = 0x4
@@ -21,6 +22,7 @@ const (
 	EPOLL_CTL_ADD = 0x1
 	EPOLL_CTL_DEL = 0x2
 	EPOLL_CTL_MOD = 0x3
+	EFD_NONBLOCK  = 0x800
 )
 
 type EpollEvent struct {

src/runtime/internal/syscall/syscall_linux.go

@@ -60,3 +60,8 @@ func EpollCtl(epfd, op, fd int32, event *EpollEvent) (errno uintptr) {
 	_, _, e := Syscall6(SYS_EPOLL_CTL, uintptr(epfd), uintptr(op), uintptr(fd), uintptr(unsafe.Pointer(event)), 0, 0)
 	return e
 }
+
+func Eventfd(initval, flags int32) (fd int32, errno uintptr) {
+	r1, _, e := Syscall6(SYS_EVENTFD2, uintptr(initval), uintptr(flags), 0, 0, 0, 0)
+	return int32(r1), e
+}

src/runtime/netpoll_epoll.go

@@ -13,11 +13,9 @@ import (
 )
 
 var (
-	epfd int32 = -1 // epoll descriptor
+	epfd           int32         = -1 // epoll descriptor
-
+	netpollEventFd uintptr            // eventfd for netpollBreak
-	netpollBreakRd, netpollBreakWr uintptr // for netpollBreak
+	netpollWakeSig atomic.Uint32      // used to avoid duplicate calls of netpollBreak
-
-	netpollWakeSig atomic.Uint32 // used to avoid duplicate calls of netpollBreak
 )
 
 func netpollinit() {
@@ -27,26 +25,25 @@ func netpollinit() {
 		println("runtime: epollcreate failed with", errno)
 		throw("runtime: netpollinit failed")
 	}
-	r, w, errpipe := nonblockingPipe()
+	efd, errno := syscall.Eventfd(0, syscall.EFD_CLOEXEC|syscall.EFD_NONBLOCK)
-	if errpipe != 0 {
+	if errno != 0 {
-		println("runtime: pipe failed with", -errpipe)
+		println("runtime: eventfd failed with", -errno)
-		throw("runtime: pipe failed")
+		throw("runtime: eventfd failed")
 	}
 	ev := syscall.EpollEvent{
 		Events: syscall.EPOLLIN,
 	}
-	*(**uintptr)(unsafe.Pointer(&ev.Data)) = &netpollBreakRd
+	*(**uintptr)(unsafe.Pointer(&ev.Data)) = &netpollEventFd
-	errno = syscall.EpollCtl(epfd, syscall.EPOLL_CTL_ADD, r, &ev)
+	errno = syscall.EpollCtl(epfd, syscall.EPOLL_CTL_ADD, efd, &ev)
 	if errno != 0 {
 		println("runtime: epollctl failed with", errno)
 		throw("runtime: epollctl failed")
 	}
-	netpollBreakRd = uintptr(r)
+	netpollEventFd = uintptr(efd)
-	netpollBreakWr = uintptr(w)
 }
 
 func netpollIsPollDescriptor(fd uintptr) bool {
-	return fd == uintptr(epfd) || fd == netpollBreakRd || fd == netpollBreakWr
+	return fd == uintptr(epfd) || fd == netpollEventFd
 }
 
 func netpollopen(fd uintptr, pd *pollDesc) uintptr {
@@ -73,10 +70,11 @@ func netpollBreak() {
 		return
 	}
 
+	var one uint64 = 1
+	oneSize := int32(unsafe.Sizeof(one))
 	for {
-		var b byte
+		n := write(netpollEventFd, noescape(unsafe.Pointer(&one)), oneSize)
-		n := write(netpollBreakWr, unsafe.Pointer(&b), 1)
+		if n == oneSize {
-		if n == 1 {
 			break
 		}
 		if n == -_EINTR {
@@ -136,17 +134,19 @@ retry:
 			continue
 		}
 
-		if *(**uintptr)(unsafe.Pointer(&ev.Data)) == &netpollBreakRd {
+		if *(**uintptr)(unsafe.Pointer(&ev.Data)) == &netpollEventFd {
 			if ev.Events != syscall.EPOLLIN {
-				println("runtime: netpoll: break fd ready for", ev.Events)
+				println("runtime: netpoll: eventfd ready for", ev.Events)
-				throw("runtime: netpoll: break fd ready for something unexpected")
+				throw("runtime: netpoll: eventfd ready for something unexpected")
 			}
 			if delay != 0 {
 				// netpollBreak could be picked up by a
-				// nonblocking poll. Only read the byte
+				// nonblocking poll. Only read the 8-byte
-				// if blocking.
+				// integer if blocking.
-				var tmp [16]byte
+				// Since EFD_SEMAPHORE was not specified,
-				read(int32(netpollBreakRd), noescape(unsafe.Pointer(&tmp[0])), int32(len(tmp)))
+				// the eventfd counter will be reset to 0.
+				var one uint64
+				read(int32(netpollEventFd), noescape(unsafe.Pointer(&one)), int32(unsafe.Sizeof(one)))
 				netpollWakeSig.Store(0)
 			}
 			continue