From 451a2eb0abf38874fb144963a44356495141465d Mon Sep 17 00:00:00 2001
From: Mikio Hara <mikioh.public.networking@gmail.com>
Date: Fri, 15 Mar 2019 05:10:08 +0900
Subject: [PATCH] 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 |  6 ++++
 src/internal/poll/read_test.go  | 62 +++++++++++++++++++++++++++++++++
 src/runtime/netpoll_aix.go      |  2 +-
 src/runtime/netpoll_epoll.go    |  2 +-
 src/runtime/netpoll_kqueue.go   |  2 +-
 src/runtime/netpoll_solaris.go  |  2 +-
 6 files changed, 72 insertions(+), 4 deletions(-)
 create mode 100644 src/internal/poll/read_test.go

diff --git a/src/internal/poll/error_test.go b/src/internal/poll/error_test.go
index 89c6e384c5..06b96f635a 100644
--- a/src/internal/poll/error_test.go
+++ b/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 {
diff --git a/src/internal/poll/read_test.go b/src/internal/poll/read_test.go
new file mode 100644
index 0000000000..b4f5236d3e
--- /dev/null
+++ b/src/internal/poll/read_test.go
@@ -0,0 +1,62 @@
+// 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
+}
diff --git a/src/runtime/netpoll_aix.go b/src/runtime/netpoll_aix.go
index b4d7de8c2a..0ad8718fe0 100644
--- a/src/runtime/netpoll_aix.go
+++ b/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)
diff --git a/src/runtime/netpoll_epoll.go b/src/runtime/netpoll_epoll.go
index 7dc8301acd..8f49309865 100644
--- a/src/runtime/netpoll_epoll.go
+++ b/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)
diff --git a/src/runtime/netpoll_kqueue.go b/src/runtime/netpoll_kqueue.go
index 1de484978a..a8880e82a5 100644
--- a/src/runtime/netpoll_kqueue.go
+++ b/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)
diff --git a/src/runtime/netpoll_solaris.go b/src/runtime/netpoll_solaris.go
index 7ae8a2aba1..b4bb40ed9b 100644
--- a/src/runtime/netpoll_solaris.go
+++ b/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)
-- 
2.50.0