net: TestTCPSelfConnect reports failure after 34 hours of stress testing.

[RLH]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

On a
rlh@rlh1:~/work/go/src$ go version
go version devel +d4b46aa Thu Dec 8 01:36:44 2016 +0000 linux/amd64

What operating system and processor architecture are you using (go env)?

rlh@rlh1:~/work/go/src$ go env
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/usr/local/google/home/rlh/work/code"
GORACE=""
GOROOT="/usr/local/google/home/rlh/work/go"
GOTOOLDIR="/usr/local/google/home/rlh/work/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build725383804=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
rlh@rlh1:~/work/go/src$ go version
go version devel +d4b46aa Thu Dec 8 01:36:44 2016 +0000 linux/amd64
rlh@rlh1:~/work/go/src$ 
rlh@rlh1:
This is a 6 core 12 thread machine.
vendor_id	: GenuineIntel
cpu family	: 6
model		: 63
model name	: Intel(R) Xeon(R) CPU E5-1650 v3 @ 3.50GHz
stepping	: 2
siblings	: 12

What did you do?

I ran ./run.bash in a simple loop using the following.
GOTRACEBACK=crash ./run.bash -no-rebuild

If possible, provide a recipe for reproducing the error.
A complete runnable program is good.
A link on play.golang.org is best.
See above.

What did you expect to see?

Success.

What did you see instead?

After a day (34 hours) 727 successful runs I got the following failure.

..snip. ...

ok mime/quotedprintable 0.162s
--- FAIL: TestTCPSelfConnect (0.13s)
tcpsock_test.go:661: Dial 127.0.0.1:48322 should fail
tcpsock_test.go:661: Dial 127.0.0.1:48324 should fail
tcpsock_test.go:661: Dial 127.0.0.1:48325 should fail
tcpsock_test.go:661: Dial 127.0.0.1:48326 should fail
tcpsock_test.go:661: Dial 127.0.0.1:48327 should fail
tcpsock_test.go:661: Dial 127.0.0.1:48328 should fail
tcpsock_test.go:661: Dial 127.0.0.1:48329 should fail
FAIL
FAIL net 1.527s
ok net/http 2.550s
ok net/http/cgi 0.495s

... snip ..

Note missing 48323.

I have not reproduced it. The only reason this is a concern is that it limits stress testing speculative parts of the GC and runtime.

[bradfitz]

/cc @mikioh @rsc

[mikioh]

Challenging against TCP simultaneous open is a bit tough job. Let's push out the test from short-mode testing except when running on buildbots.

[bradfitz]

If the test just rarely catches the bug, I'd rather not sweet it under the rug by making it run less often.

Is this not a real bug?

If so, what's the bug.
If not, I'd rather deflake it.

[mikioh]

Is this not a real bug?

I'm confused. The fix (https://codereview.appspot.com/5650071) was approved by you. I'm not sure what you are asking for.

My understanding is that TCP simultaneous open is a valid behavior of TCP and the fix written by @rsc was just a try to mitigate some undesirable side effect of the behavior for helping some application. But that might be a compromise. I think it's basically impossible to avoid TCP simultaneous open completely unless we have full control of each TCP FSM and IP control block inside the kernel.

[ianlancetaylor]

I don't see any GNU/Linux failures of TestTCPSelfConnect in the builders at all. I do see a few failures on Solaris; for example: https://build.golang.org/log/5315cb250600796a1ffe1c4c3a8c3f626769b692.

[mikesmitty]

Happened to run into this one as well with 1.11rc2 on CentOS 7 x86_64:

--- FAIL: TestTCPSelfConnect (0.13s)
    tcpsock_test.go:665: Dial 127.0.0.1:41378 should fail
    tcpsock_test.go:665: Dial 127.0.0.1:41380 should fail
    tcpsock_test.go:665: Dial 127.0.0.1:41382 should fail
    tcpsock_test.go:665: Dial 127.0.0.1:41384 should fail
    tcpsock_test.go:665: Dial 127.0.0.1:41386 should fail
    tcpsock_test.go:665: Dial 127.0.0.1:41388 should fail
    tcpsock_test.go:665: Dial 127.0.0.1:41390 should fail
    tcpsock_test.go:665: Dial 127.0.0.1:41392 should fail
    tcpsock_test.go:665: Dial 127.0.0.1:41396 should fail
FAIL
FAIL	net	2.418s