net: fix testHookCanceledDial race

Loading and calling testHookCanceledDial in the function passed to
context.AfterFunc is racey, because the function runs in a separate
goroutine, and is not synchronized with the test code that restores
the original testHookCanceledDial value.

We could add a channel and wait for the "AfterFunc" to return in
the deferred function, but that's a lot of synchronization overhead
just for a bit of test code. Instead we simply load
testHookCanceledDial into a local variable synchronously. This fixes
the race without introducing any overhead.

Fixes #75474

Change-Id: If8fbd0f5f65375577c2ded64a13a15b406c45ecc
Reviewed-on: https://go-review.googlesource.com/c/go/+/704455
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>
Auto-Submit: Damien Neil <dneil@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

diff --git a/src/net/fd_unix.go b/src/net/fd_unix.go
index 40ecbef2e89f346358c1a4a6f849a747d02891c9..0d4303e2cc0cbee5e64f9bad4c647bc541678c5d 100644 (file)
--- a/src/net/fd_unix.go
+++ b/src/net/fd_unix.go
@@ -82,6 +82,9 @@ func (fd *netFD) connect(ctx context.Context, la, ra syscall.Sockaddr) (rsa sysc
                        defer fd.pfd.SetWriteDeadline(noDeadline)
                }
 
+               // Load the hook function synchronously to prevent a race
+               // with test code that restores the old value.
+               testHookCanceledDial := testHookCanceledDial
                stop := context.AfterFunc(ctx, func() {
                        // Force the runtime's poller to immediately give up
                        // waiting for writability, unblocking waitWrite