From: qmuntal <quimmuntal@gmail.com>
Date: Tue, 8 Apr 2025 13:31:02 +0000 (+0200)
Subject: internal/poll: fix race in Close
X-Git-Tag: go1.25rc1~509
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=cac276f81a5ff11ae3c9027c45d14469f2b7fb70;p=gostls13.git

internal/poll: fix race in Close

There is a potential race between a concurrent call to FD.initIO, which
calls FD.pd.init, and a call to FD.Close, which calls FD.pd.evict.

This is solved by calling FD.initIO in FD.Close, as that will block
until the concurrent FD.initIO has completed. Note that FD.initIO is
no-op if first called from here.

The race window is so small that it is not possible to write a test
that triggers it.

Change-Id: Ie2f2818e746b9d626fe3b9eb6b8ff967c81ef863
Reviewed-on: https://go-review.googlesource.com/c/go/+/663815
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
---

diff --git a/src/internal/poll/fd_windows.go b/src/internal/poll/fd_windows.go
index 6660bcd959..99891de763 100644
--- a/src/internal/poll/fd_windows.go
+++ b/src/internal/poll/fd_windows.go
@@ -336,6 +336,10 @@ func (fd *FD) initIO() error {
 		return nil
 	}
 	fd.initIOOnce.Do(func() {
+		if fd.closing() {
+			// Closing, nothing to do.
+			return
+		}
 		// The runtime poller will ignore I/O completion
 		// notifications not initiated by this package,
 		// so it is safe to add handles owned by the caller.
@@ -434,6 +438,12 @@ func (fd *FD) Close() error {
 	if !fd.fdmu.increfAndClose() {
 		return errClosing(fd.isFile)
 	}
+	// There is a potential race between a concurrent call to fd.initIO,
+	// which calls fd.pd.init, and the call to fd.pd.evict below.
+	// This is solved by calling fd.initIO ourselves, which will
+	// block until the concurrent fd.initIO has completed. Note
+	// that fd.initIO is no-op if first called from here.
+	fd.initIO()
 	if fd.kind == kindPipe {
 		syscall.CancelIoEx(fd.Sysfd, nil)
 	}