runtime: for kqueue treat EVFILT_READ with EV_EOF as permitting a write
On systems that use kqueue, we always register descriptors for both
EVFILT_READ and EVFILT_WRITE. On at least FreeBSD and OpenBSD, when
the write end of a pipe is registered for EVFILT_READ and EVFILT_WRITE
events, and the read end of the pipe is closed, kqueue reports an
EVFILT_READ event with EV_EOF set, but does not report an EVFILT_WRITE
event. Since the write to the pipe is waiting for an EVFILT_WRITE
event, closing the read end of a pipe can cause the write end to hang
rather than attempt another write which will fail with EPIPE.
Fix this by treating EVFILT_READ with EV_EOF set as making both reads
and writes ready to proceed.
The real test for this is in CL 71770, which tests using various
timeouts with pipes.
Updates #22114
Change-Id: Ib23fbaaddbccd8eee77bdf18f27a7f0aa50e2742
Reviewed-on: https://go-review.googlesource.com/71973
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
diff --git a/src/internal/poll/fd_unix.go b/src/internal/poll/fd_unix.go
index c51370a..3ac6927 100644
--- a/src/internal/poll/fd_unix.go
+++ b/src/internal/poll/fd_unix.go
@@ -411,6 +411,15 @@
return fd.pd.waitWrite(fd.isFile)
}
+// WriteOnce is for testing only. It makes a single write call.
+func (fd *FD) WriteOnce(p []byte) (int, error) {
+ if err := fd.writeLock(); err != nil {
+ return 0, err
+ }
+ defer fd.writeUnlock()
+ return syscall.Write(fd.Sysfd, p)
+}
+
// RawControl invokes the user-defined function f for a non-IO
// operation.
func (fd *FD) RawControl(f func(uintptr)) error {
diff --git a/src/net/write_unix_test.go b/src/net/write_unix_test.go
new file mode 100644
index 0000000..6d8cb6a
--- /dev/null
+++ b/src/net/write_unix_test.go
@@ -0,0 +1,66 @@
+// Copyright 2017 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.
+
+// +build darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package net
+
+import (
+ "bytes"
+ "syscall"
+ "testing"
+ "time"
+)
+
+// Test that a client can't trigger an endless loop of write system
+// calls on the server by shutting down the write side on the client.
+// Possibility raised in the discussion of https://golang.org/cl/71973.
+func TestEndlessWrite(t *testing.T) {
+ t.Parallel()
+ c := make(chan bool)
+ server := func(cs *TCPConn) error {
+ cs.CloseWrite()
+ <-c
+ return nil
+ }
+ client := func(ss *TCPConn) error {
+ // Tell the server to return when we return.
+ defer close(c)
+
+ // Loop writing to the server. The server is not reading
+ // anything, so this will eventually block, and then time out.
+ b := bytes.Repeat([]byte{'a'}, 8192)
+ cagain := 0
+ for {
+ n, err := ss.conn.fd.pfd.WriteOnce(b)
+ if n > 0 {
+ cagain = 0
+ }
+ switch err {
+ case nil:
+ case syscall.EAGAIN:
+ if cagain == 0 {
+ // We've written enough data to
+ // start blocking. Set a deadline
+ // so that we will stop.
+ ss.SetWriteDeadline(time.Now().Add(5 * time.Millisecond))
+ }
+ cagain++
+ if cagain > 20 {
+ t.Error("looping on EAGAIN")
+ return nil
+ }
+ if err = ss.conn.fd.pfd.WaitWrite(); err != nil {
+ t.Logf("client WaitWrite: %v", err)
+ return nil
+ }
+ default:
+ // We expect to eventually get an error.
+ t.Logf("client WriteOnce: %v", err)
+ return nil
+ }
+ }
+ }
+ withTCPConnPair(t, client, server)
+}
diff --git a/src/runtime/defs1_netbsd_386.go b/src/runtime/defs1_netbsd_386.go
index 66f07ce..c26f417 100644
--- a/src/runtime/defs1_netbsd_386.go
+++ b/src/runtime/defs1_netbsd_386.go
@@ -79,6 +79,7 @@
_EV_CLEAR = 0x20
_EV_RECEIPT = 0
_EV_ERROR = 0x4000
+ _EV_EOF = 0x8000
_EVFILT_READ = 0x0
_EVFILT_WRITE = 0x1
)
diff --git a/src/runtime/defs1_netbsd_amd64.go b/src/runtime/defs1_netbsd_amd64.go
index 9e31471..0704cd4 100644
--- a/src/runtime/defs1_netbsd_amd64.go
+++ b/src/runtime/defs1_netbsd_amd64.go
@@ -79,6 +79,7 @@
_EV_CLEAR = 0x20
_EV_RECEIPT = 0
_EV_ERROR = 0x4000
+ _EV_EOF = 0x8000
_EVFILT_READ = 0x0
_EVFILT_WRITE = 0x1
)
diff --git a/src/runtime/defs1_netbsd_arm.go b/src/runtime/defs1_netbsd_arm.go
index db8e4c6..d2a13ad 100644
--- a/src/runtime/defs1_netbsd_arm.go
+++ b/src/runtime/defs1_netbsd_arm.go
@@ -79,6 +79,7 @@
_EV_CLEAR = 0x20
_EV_RECEIPT = 0
_EV_ERROR = 0x4000
+ _EV_EOF = 0x8000
_EVFILT_READ = 0x0
_EVFILT_WRITE = 0x1
)
diff --git a/src/runtime/defs_darwin.go b/src/runtime/defs_darwin.go
index 78df4e7..f7d65e7 100644
--- a/src/runtime/defs_darwin.go
+++ b/src/runtime/defs_darwin.go
@@ -139,6 +139,7 @@
EV_CLEAR = C.EV_CLEAR
EV_RECEIPT = C.EV_RECEIPT
EV_ERROR = C.EV_ERROR
+ EV_EOF = C.EV_EOF
EVFILT_READ = C.EVFILT_READ
EVFILT_WRITE = C.EVFILT_WRITE
)
diff --git a/src/runtime/defs_darwin_386.go b/src/runtime/defs_darwin_386.go
index 1a5967b..f6dbcc5 100644
--- a/src/runtime/defs_darwin_386.go
+++ b/src/runtime/defs_darwin_386.go
@@ -118,6 +118,7 @@
_EV_CLEAR = 0x20
_EV_RECEIPT = 0x40
_EV_ERROR = 0x4000
+ _EV_EOF = 0x8000
_EVFILT_READ = -0x1
_EVFILT_WRITE = -0x2
)
diff --git a/src/runtime/defs_darwin_amd64.go b/src/runtime/defs_darwin_amd64.go
index a4ab090..245fe15 100644
--- a/src/runtime/defs_darwin_amd64.go
+++ b/src/runtime/defs_darwin_amd64.go
@@ -118,6 +118,7 @@
_EV_CLEAR = 0x20
_EV_RECEIPT = 0x40
_EV_ERROR = 0x4000
+ _EV_EOF = 0x8000
_EVFILT_READ = -0x1
_EVFILT_WRITE = -0x2
)
diff --git a/src/runtime/defs_darwin_arm.go b/src/runtime/defs_darwin_arm.go
index 3f8dbbf..f89aee6 100644
--- a/src/runtime/defs_darwin_arm.go
+++ b/src/runtime/defs_darwin_arm.go
@@ -120,6 +120,7 @@
_EV_CLEAR = 0x20
_EV_RECEIPT = 0x40
_EV_ERROR = 0x4000
+ _EV_EOF = 0x8000
_EVFILT_READ = -0x1
_EVFILT_WRITE = -0x2
)
diff --git a/src/runtime/defs_darwin_arm64.go b/src/runtime/defs_darwin_arm64.go
index c25a41b..a0ca7f1 100644
--- a/src/runtime/defs_darwin_arm64.go
+++ b/src/runtime/defs_darwin_arm64.go
@@ -118,6 +118,7 @@
_EV_CLEAR = 0x20
_EV_RECEIPT = 0x40
_EV_ERROR = 0x4000
+ _EV_EOF = 0x8000
_EVFILT_READ = -0x1
_EVFILT_WRITE = -0x2
)
diff --git a/src/runtime/defs_dragonfly.go b/src/runtime/defs_dragonfly.go
index ed00be0..95014fe 100644
--- a/src/runtime/defs_dragonfly.go
+++ b/src/runtime/defs_dragonfly.go
@@ -103,6 +103,7 @@
EV_DELETE = C.EV_DELETE
EV_CLEAR = C.EV_CLEAR
EV_ERROR = C.EV_ERROR
+ EV_EOF = C.EV_EOF
EVFILT_READ = C.EVFILT_READ
EVFILT_WRITE = C.EVFILT_WRITE
)
diff --git a/src/runtime/defs_dragonfly_amd64.go b/src/runtime/defs_dragonfly_amd64.go
index fc70103..c30da80 100644
--- a/src/runtime/defs_dragonfly_amd64.go
+++ b/src/runtime/defs_dragonfly_amd64.go
@@ -82,6 +82,7 @@
_EV_DELETE = 0x2
_EV_CLEAR = 0x20
_EV_ERROR = 0x4000
+ _EV_EOF = 0x8000
_EVFILT_READ = -0x1
_EVFILT_WRITE = -0x2
)
diff --git a/src/runtime/defs_freebsd.go b/src/runtime/defs_freebsd.go
index 0a11d09..9d55111 100644
--- a/src/runtime/defs_freebsd.go
+++ b/src/runtime/defs_freebsd.go
@@ -125,6 +125,7 @@
EV_CLEAR = C.EV_CLEAR
EV_RECEIPT = C.EV_RECEIPT
EV_ERROR = C.EV_ERROR
+ EV_EOF = C.EV_EOF
EVFILT_READ = C.EVFILT_READ
EVFILT_WRITE = C.EVFILT_WRITE
)
diff --git a/src/runtime/defs_freebsd_386.go b/src/runtime/defs_freebsd_386.go
index 92b0550..49bcbb1 100644
--- a/src/runtime/defs_freebsd_386.go
+++ b/src/runtime/defs_freebsd_386.go
@@ -95,6 +95,7 @@
_EV_CLEAR = 0x20
_EV_RECEIPT = 0x40
_EV_ERROR = 0x4000
+ _EV_EOF = 0x8000
_EVFILT_READ = -0x1
_EVFILT_WRITE = -0x2
)
diff --git a/src/runtime/defs_freebsd_amd64.go b/src/runtime/defs_freebsd_amd64.go
index 645e205..0e1c675 100644
--- a/src/runtime/defs_freebsd_amd64.go
+++ b/src/runtime/defs_freebsd_amd64.go
@@ -95,6 +95,7 @@
_EV_CLEAR = 0x20
_EV_RECEIPT = 0x40
_EV_ERROR = 0x4000
+ _EV_EOF = 0x8000
_EVFILT_READ = -0x1
_EVFILT_WRITE = -0x2
)
diff --git a/src/runtime/defs_freebsd_arm.go b/src/runtime/defs_freebsd_arm.go
index c8a198f..71684fe 100644
--- a/src/runtime/defs_freebsd_arm.go
+++ b/src/runtime/defs_freebsd_arm.go
@@ -95,6 +95,7 @@
_EV_CLEAR = 0x20
_EV_RECEIPT = 0x40
_EV_ERROR = 0x4000
+ _EV_EOF = 0x8000
_EVFILT_READ = -0x1
_EVFILT_WRITE = -0x2
)
diff --git a/src/runtime/defs_netbsd.go b/src/runtime/defs_netbsd.go
index 56db1f0..41aa07a 100644
--- a/src/runtime/defs_netbsd.go
+++ b/src/runtime/defs_netbsd.go
@@ -105,6 +105,7 @@
EV_CLEAR = C.EV_CLEAR
EV_RECEIPT = 0
EV_ERROR = C.EV_ERROR
+ EV_EOF = C.EV_EOF
EVFILT_READ = C.EVFILT_READ
EVFILT_WRITE = C.EVFILT_WRITE
)
diff --git a/src/runtime/defs_openbsd.go b/src/runtime/defs_openbsd.go
index 7e72150..9ff13df 100644
--- a/src/runtime/defs_openbsd.go
+++ b/src/runtime/defs_openbsd.go
@@ -100,6 +100,7 @@
EV_DELETE = C.EV_DELETE
EV_CLEAR = C.EV_CLEAR
EV_ERROR = C.EV_ERROR
+ EV_EOF = C.EV_EOF
EVFILT_READ = C.EVFILT_READ
EVFILT_WRITE = C.EVFILT_WRITE
)
diff --git a/src/runtime/defs_openbsd_386.go b/src/runtime/defs_openbsd_386.go
index ce08111..1185530 100644
--- a/src/runtime/defs_openbsd_386.go
+++ b/src/runtime/defs_openbsd_386.go
@@ -80,6 +80,7 @@
_EV_DELETE = 0x2
_EV_CLEAR = 0x20
_EV_ERROR = 0x4000
+ _EV_EOF = 0x8000
_EVFILT_READ = -0x1
_EVFILT_WRITE = -0x2
)
diff --git a/src/runtime/defs_openbsd_amd64.go b/src/runtime/defs_openbsd_amd64.go
index ea07098..4bb8eac 100644
--- a/src/runtime/defs_openbsd_amd64.go
+++ b/src/runtime/defs_openbsd_amd64.go
@@ -80,6 +80,7 @@
_EV_DELETE = 0x2
_EV_CLEAR = 0x20
_EV_ERROR = 0x4000
+ _EV_EOF = 0x8000
_EVFILT_READ = -0x1
_EVFILT_WRITE = -0x2
)
diff --git a/src/runtime/defs_openbsd_arm.go b/src/runtime/defs_openbsd_arm.go
index b0fb639..38b77c9 100644
--- a/src/runtime/defs_openbsd_arm.go
+++ b/src/runtime/defs_openbsd_arm.go
@@ -80,6 +80,7 @@
_EV_DELETE = 0x2
_EV_CLEAR = 0x20
_EV_ERROR = 0x4000
+ _EV_EOF = 0x8000
_EVFILT_READ = -0x1
_EVFILT_WRITE = -0x2
)
diff --git a/src/runtime/netpoll_kqueue.go b/src/runtime/netpoll_kqueue.go
index 71de98b..4d5d1a4 100644
--- a/src/runtime/netpoll_kqueue.go
+++ b/src/runtime/netpoll_kqueue.go
@@ -88,10 +88,23 @@
for i := 0; i < int(n); i++ {
ev := &events[i]
var mode int32
- if ev.filter == _EVFILT_READ {
+ switch ev.filter {
+ case _EVFILT_READ:
mode += 'r'
- }
- if ev.filter == _EVFILT_WRITE {
+
+ // On some systems when the read end of a pipe
+ // is closed the write end will not get a
+ // _EVFILT_WRITE event, but will get a
+ // _EVFILT_READ event with EV_EOF set.
+ // Note that setting 'w' here just means that we
+ // will wake up a goroutine waiting to write;
+ // that goroutine will try the write again,
+ // and the appropriate thing will happen based
+ // on what that write returns (success, EPIPE, EAGAIN).
+ if ev.flags&_EV_EOF != 0 {
+ mode += 'w'
+ }
+ case _EVFILT_WRITE:
mode += 'w'
}
if mode != 0 {
