runtime: netpollBreak write failed with 1

[zouyonghao]

What version of Go are you using (go version)?

go version go1.17.2 linux/amd64

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

go env Output

GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/zyh/.cache/go-build"
GOENV="/home/zyh/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/zyh/go_workspace/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/zyh/go_workspace"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/zyh/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/zyh/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.17.2"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build3831048988=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Run etcd and the write syscall returns -1

What did you expect to see?

According to the man page of syscall write, it

On success, the number of bytes written is returned.  On error,
       -1 is returned, and errno is set to indicate the error.

So -1 is a common case for write, but the program fails in this case.

What did you see instead?

The runtime should handle this error, but the code in netpoll_epoll.go and netpoll_kqueue.go seems not.

go/src/runtime/netpoll_epoll.go

Lines 85 to 96 in e8cda0a

	n := write(netpollBreakWr, unsafe.Pointer(&b), 1)
	if n == 1 {
	break
	}
	if n == -_EINTR {
	continue
	}
	if n == -_EAGAIN {
	return
	}
	println("runtime: netpollBreak write failed with", -n)
	throw("runtime: netpollBreak write failed")

The piece of code shows that it handles the return number of write, but it seems the return value can only be the length of write, which is 1 in this case, and -1 that indicates error. And we should use the errno to know what the error is.

[zouyonghao]

Oops, I forgot that go uses the raw system call which just returns the error code.