runtime, internal/poll: report only critical event scanning error

This change makes the runtime-integrated network poller report only
critical event scanning errors.

In the previous attempt, CL 166497, we treated any combination of error
events as event scanning errors and it caused false positives in event
waiters because platform-dependent event notification mechanisms allow
event originators to use various combination of events.

To avoid false positives, this change makes the poller treat an
individual error event as a critical event scanning error by the
convention of event notification mechanism implementations.

Updates #30624.
Fixes #30817.
Fixes #30840.

Change-Id: I906c9e83864527ff73f636fd02bab854d54684ea
Reviewed-on: https://go-review.googlesource.com/c/go/+/167777
Run-TryBot: Mikio Hara <mikioh.public.networking@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/internal/poll/error_test.go

@@ -9,6 +9,7 @@ import (
 	"net"
 	"os"
 	"testing"
+	"time"
 )
 
 func TestReadError(t *testing.T) {
@@ -18,6 +19,11 @@ func TestReadError(t *testing.T) {
 			t.Skip(err)
 		}
 		defer f.Close()
+
+		// Give scheduler a chance to have two separated
+		// goroutines: an event poller and an event waiter.
+		time.Sleep(100 * time.Millisecond)
+
 		var b [1]byte
 		_, err = f.Read(b[:])
 		if perr := parseReadError(err, isBadStateFileError); perr != nil {

src/internal/poll/read_test.go

+// Copyright 2019 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 poll_test
+
+import (
+	"io/ioutil"
+	"os"
+	"runtime"
+	"sync"
+	"testing"
+	"time"
+)
+
+func TestRead(t *testing.T) {
+	t.Run("SpecialFile", func(t *testing.T) {
+		var wg sync.WaitGroup
+		for _, p := range specialFiles() {
+			for i := 0; i < 4; i++ {
+				wg.Add(1)
+				go func(p string) {
+					defer wg.Done()
+					for i := 0; i < 100; i++ {
+						if _, err := ioutil.ReadFile(p); err != nil {
+							t.Error(err)
+							return
+						}
+						time.Sleep(time.Nanosecond)
+					}
+				}(p)
+			}
+		}
+		wg.Wait()
+	})
+}
+
+func specialFiles() []string {
+	var ps []string
+	switch runtime.GOOS {
+	case "darwin", "dragonfly", "freebsd", "netbsd", "openbsd":
+		ps = []string{
+			"/dev/null",
+		}
+	case "linux":
+		ps = []string{
+			"/dev/null",
+			"/proc/stat",
+			"/sys/devices/system/cpu/online",
+		}
+	}
+	nps := ps[:0]
+	for _, p := range ps {
+		f, err := os.Open(p)
+		if err != nil {
+			continue
+		}
+		f.Close()
+		nps = append(nps, p)
+	}
+	return nps
+}

src/runtime/netpoll_aix.go

@@ -233,7 +233,7 @@ retry:
 				println("*** netpollready i=", i, "revents=", pfd.revents, "events=", pfd.events, "pd=", pds[i])
 			}
 			pds[i].everr = false
-			if pfd.revents&_POLLERR != 0 {
+			if pfd.revents == _POLLERR {
 				pds[i].everr = true
 			}
 			netpollready(&toRun, pds[i], mode)

src/runtime/netpoll_epoll.go

@@ -92,7 +92,7 @@ retry:
 		if mode != 0 {
 			pd := *(**pollDesc)(unsafe.Pointer(&ev.data))
 			pd.everr = false
-			if ev.events&_EPOLLERR != 0 {
+			if ev.events == _EPOLLERR {
 				pd.everr = true
 			}
 			netpollready(&toRun, pd, mode)

src/runtime/netpoll_kqueue.go

@@ -104,7 +104,7 @@ retry:
 		if mode != 0 {
 			pd := (*pollDesc)(unsafe.Pointer(ev.udata))
 			pd.everr = false
-			if ev.flags&_EV_ERROR != 0 {
+			if ev.flags == _EV_ERROR {
 				pd.everr = true
 			}
 			netpollready(&toRun, pd, mode)

src/runtime/netpoll_solaris.go

@@ -234,7 +234,7 @@ retry:
 
 		if mode != 0 {
 			pd.everr = false
-			if ev.portev_events&_POLLERR != 0 {
+			if ev.portev_events == _POLLERR {
 				pd.everr = true
 			}
 			netpollready(&toRun, pd, mode)