net: call to Dial results in "all goroutines are asleep"

[mcwalrus]

Go version

go1.25.6 playground

Output of go env in your module/workspace:

N/A - reproduce found in playground

What did you do?

Found deadlock race condition case with example test:

https://pkg.go.dev/context#example-AfterFunc-Connection

fatal error: all goroutines are asleep - deadlock!

goroutine 1 [IO wait]:
internal/poll.runtime_pollWait(0x7ebd7704cc00, 0x77)
	/usr/local/go-faketime/src/runtime/netpoll.go:351 +0x85
internal/poll.(*pollDesc).wait(0xc0000f2180?, 0x516dde?, 0x0)
	/usr/local/go-faketime/src/internal/poll/fd_poll_runtime.go:84 +0x27
internal/poll.(*pollDesc).waitWrite(...)
	/usr/local/go-faketime/src/internal/poll/fd_poll_runtime.go:93
internal/poll.(*FD).WaitWrite(...)
	/usr/local/go-faketime/src/internal/poll/fd_unix.go:685
net.(*netFD).connect(0xc0000f2180, {0x547fb0, 0x6218e0}, {0x4164f4?, 0x0?}, {0x547948?, 0xc0000b6100?})
	/usr/local/go-faketime/src/net/fd_unix.go:130 +0x6b6
net.(*netFD).dial(0xc0000f2180, {0x547fb0, 0x6218e0}, {0x5485b8?, 0x0?}, {0x5485b8, 0xc0000aa630}, 0x7ebd77325470?)
	/usr/local/go-faketime/src/net/sock_posix.go:124 +0x3bc
net.socket({0x547fb0, 0x6218e0}, {0x516dde, 0x3}, 0x2, 0x1, 0xc000002380?, 0x0, {0x5485b8, 0x0}, ...)
	/usr/local/go-faketime/src/net/sock_posix.go:70 +0x29b
net.internetSocket({0x547fb0, 0x6218e0}, {0x516dde, 0x3}, {0x5485b8, 0x0}, {0x5485b8, 0xc0000aa630}, 0x1, 0x0, ...)
	/usr/local/go-faketime/src/net/ipsock_posix.go:167 +0xf8
net.(*sysDialer).doDialTCPProto(0xc0000f8000, {0x547fb0, 0x6218e0}, 0x0, 0xc0000aa630, 0x0)
	/usr/local/go-faketime/src/net/tcpsock_posix.go:85 +0xe7
net.(*sysDialer).doDialTCP(...)
	/usr/local/go-faketime/src/net/tcpsock_posix.go:75
net.(*sysDialer).dialTCP(0x28?, {0x547fb0?, 0x6218e0?}, 0xc0000789f0?, 0x4cfa66?)
	/usr/local/go-faketime/src/net/tcpsock_posix.go:71 +0x69
net.(*sysDialer).dialSingle(0xc0000f8000, {0x547fb0, 0x6218e0}, {0x547e28, 0xc0000aa630})
	/usr/local/go-faketime/src/net/dial.go:721 +0x3ce
net.(*sysDialer).dialSerial(0xc0000f8000, {0x547fb0, 0x6218e0}, {0xc0000b4130?, 0x1, 0x1c?})
	/usr/local/go-faketime/src/net/dial.go:686 +0x248
net.(*sysDialer).dialParallel(0x0?, {0x547fb0?, 0x6218e0?}, {0xc0000b4130?, 0x4f6320?, 0x516e95?}, {0x0?, 0x516dde?, 0x7ebd7731a5c0?})
	/usr/local/go-faketime/src/net/dial.go:587 +0x30a
net.(*Dialer).DialContext(0xc000078d90, {0x547fb0, 0x6218e0}, {0x516dde, 0x3}, {0xc0000be140, 0xf})
	/usr/local/go-faketime/src/net/dial.go:578 +0x6a9
net.(*Dialer).Dial(...)
	/usr/local/go-faketime/src/net/dial.go:504
net.Dial({0x516dde?, 0x490013?}, {0xc0000be140?, 0x415b77?})
	/usr/local/go-faketime/src/net/dial.go:471 +0x77
main.main()
	/tmp/sandbox917687343/prog.go:35 +0x132

What did you see happen?

Occasional fatal error when trying example test.

What did you expect to see?

Examples from the standard library are expected to work.

[gabyhelp]

Related Issues

• x/website: Inside the Go Playground - Faking the network example error #53731 (closed)
• runtime: TestNetpollDeadlock fails on Linux in go1.9.1 #22280 (closed)
• runtime: TestNetpollDeadlock failure on darwin/amd64 #22403 (closed)
• net: TestDialParallel leaks worker goroutines and inflight sockets #11878 (closed)
• net/http: TestCancelRequestWithChannelBeforeDo_Cancel failure on Windows long test #35122 (closed)
• runtime: TestNetpollDeadlock is failing #42500 (closed)
• Playground produces flaky results when using net/http/httptest.NewServer #47936 (closed)
• net: TestDialParallelSpuriousConnection occasionally times out #34495 (closed)
• context: misuse of `sync.Cond` in `ExampleAfterFunc_cond` #62180 (closed)
• x/playground: Faking the network example periodically deadlocks #48394

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[linsite]

This is a deadlock rather than a race condition.

[cagedmantis]

cc @neild @Sajmani

[adonovan]

cc: @ianlancetaylor @prattmic for net poller.

[prattmic]

I haven't looked closely, but this is likely specific to the faketime mode used by playground (time is fake on the playground in a manner similar to testing/synctest, though a completely different implementation).

My guess is that SetReadDeadline doesn't work properly in faketime mode.

cc @golang/runtime