testing: go 1.17 regression: deadlock in test suite

[tbonfort]

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

$ go version
go version go1.17 linux/amd64

Does this issue reproduce with the latest release?

yes

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/tbonfort/.cache/go-build"
GOENV="/home/tbonfort/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/tbonfort/go/pkg/mod"
GOOS="linux"
GOPATH="/home/tbonfort/go"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.17"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build2515039918=/tmp/go-build -gno-record-gcc-switches"

What did you do?

My cgo testsuite deadlocks, commenting out a seemingly random cgo call from 2 tests before the deadlock happens fixes the issue.

Failing test run:

...snip...
=== RUN   TestOpen
--- PASS: TestOpen (0.00s)
=== RUN   TestOpenUpdate
--- PASS: TestOpenUpdate (0.00s)
=== RUN   TestClosingErrors
--- PASS: TestClosingErrors (0.00s)
=== RUN   TestOpenShared
--- PASS: TestOpenShared (0.00s)
=== RUN   TestRegister
--- PASS: TestRegister (0.00s)
^Csignal: interrupt
FAIL	github.com/airbusgeo/godal	9.929s

Commenting out this line in the TestOpenShared test fixes the deadlock:
https://github.com/airbusgeo/godal/blob/00980a3df723677b2d949a10eedd78ab6c5d6aee/godal_test.go#L1242

Here is a gdb stacktrace when deadlocked:

sudo gdb ~/dev/godal/godal.test 1904477
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Reading symbols from /home/tbonfort/dev/godal/godal.test...
Attaching to program: /home/tbonfort/dev/godal/godal.test, process 1904477
[New LWP 1904478]
[New LWP 1904479]
[New LWP 1904480]
[New LWP 1904481]
[New LWP 1904482]
Error while reading shared library symbols for /lib/x86_64-linux-gnu/libpthread.so.0:
Cannot find user-level thread for LWP 1904482: generic error
runtime.futex () at /usr/local/go/src/runtime/sys_linux_amd64.s:520
520		MOVL	AX, ret+40(FP)
Loading Go Runtime support.
(gdb) bt
#0  runtime.futex () at /usr/local/go/src/runtime/sys_linux_amd64.s:520
#1  0x000000000043b6f6 in runtime.futexsleep (addr=0xfffffffffffffe00, val=2, ns=4670691) at /usr/local/go/src/runtime/os_linux.go:44
#2  0x00000000004155f9 in runtime.lock2 (l=0xfffffffffffffe00) at /usr/local/go/src/runtime/lock_futex.go:107
#3  0x0000000000410318 in runtime.lockWithRank (l=0x4744e3 <runtime.futex+35>, rank=<optimized out>)
    at /usr/local/go/src/runtime/lockrank_off.go:23
#4  runtime.lock (l=0x4744e3 <runtime.futex+35>) at /usr/local/go/src/runtime/lock_futex.go:48
#5  runtime.chanrecv (c=0xc0001cd340, ep=0xc00025fb67, block=true) at /usr/local/go/src/runtime/chan.go:508
#6  0x0000000000410198 in runtime.chanrecv1 (c=0xfffffffffffffe00, elem=0x2) at /usr/local/go/src/runtime/chan.go:439
#7  0x0000000000513d95 in testing.(*T).Run (t=0xc0003b41a0, name=..., f={void (testing.T *)} 0xc00025fbd8)
    at /usr/local/go/src/testing/testing.go:1307
#8  0x00000000005159ae in testing.runTests.func1 (t=0xc000283040) at /usr/local/go/src/testing/testing.go:1598
#9  0x0000000000513142 in testing.tRunner (t=0xc000283040, fn={void (testing.T *)} 0xc00025fc68)
    at /usr/local/go/src/testing/testing.go:1259
#10 0x000000000051585f in testing.runTests (matchString={void (string, string, bool *, error *)} 0xc00025fd10, 
    tests=[]testing.InternalTest = {...}, deadline=...) at /usr/local/go/src/testing/testing.go:1596
#11 0x00000000005145bd in testing.(*M).Run (m=0xc00011c800, code=0) at /usr/local/go/src/testing/testing.go:1504
#12 0x00000000009ca56b in main.main () at _testmain.go:177
(gdb) thread apply all bt

Thread 6 (LWP 1904482 "godal.test"):
#0  runtime.futex () at /usr/local/go/src/runtime/sys_linux_amd64.s:520
#1  0x000000000043b6f6 in runtime.futexsleep (addr=0xfffffffffffffe00, val=0, ns=4670691) at /usr/local/go/src/runtime/os_linux.go:44
#2  0x0000000000415947 in runtime.notesleep (n=0xfffffffffffffe00) at /usr/local/go/src/runtime/lock_futex.go:160
#3  0x00000000004461d1 in runtime.templateThread () at /usr/local/go/src/runtime/proc.go:2385
#4  0x0000000000444c93 in runtime.mstart1 () at /usr/local/go/src/runtime/proc.go:1407
#5  0x0000000000444bd9 in runtime.mstart0 () at /usr/local/go/src/runtime/proc.go:1365
#6  0x0000000000470445 in runtime.mstart () at /usr/local/go/src/runtime/asm_amd64.s:248
#7  0x0000000000474b65 in runtime.mstart () at <autogenerated>:1
#8  0x00000000009d00b2 in crosscall_amd64 () at gcc_amd64.S:40
#9  0x00007fb86affd640 in ?? ()
#10 0x0000000000000000 in ?? ()

Thread 5 (LWP 1904481 "godal.test"):
#0  runtime.epollwait () at /usr/local/go/src/runtime/sys_linux_amd64.s:666
#1  0x000000000043b45c in runtime.netpoll (delay=<optimized out>) at /usr/local/go/src/runtime/netpoll_epoll.go:127
#2  0x00000000004474d3 in runtime.findrunnable () at /usr/local/go/src/runtime/proc.go:2947
#3  0x00000000004486d9 in runtime.schedule () at /usr/local/go/src/runtime/proc.go:3367
#4  0x0000000000448c2d in runtime.park_m (gp=0xc000282340) at /usr/local/go/src/runtime/proc.go:3516
#5  0x00000000004704c3 in runtime.mcall () at /usr/local/go/src/runtime/asm_amd64.s:307
#6  0xf934f160b63ffd00 in ?? ()
#7  0x0000000000800000 in text/template/parse.(*lexer).errorf (l=0x0, format=..., args=...) at /usr/local/go/src/text/template/parse/lex.go:188
#8  text/template/parse.lexComment (l=0x0) at /usr/local/go/src/text/template/parse/lex.go:319
#9  0x0000000000000000 in ?? ()

Thread 4 (LWP 1904480 "godal.test"):
#0  runtime.futex () at /usr/local/go/src/runtime/sys_linux_amd64.s:520
--Type <RET> for more, q to quit, c to continue without paging-- 
#1  0x000000000043b6f6 in runtime.futexsleep (addr=0xfffffffffffffe00, val=0, ns=4670691) at /usr/local/go/src/runtime/os_linux.go:44
#2  0x0000000000415947 in runtime.notesleep (n=0xfffffffffffffe00) at /usr/local/go/src/runtime/lock_futex.go:160
#3  0x0000000000444d8a in runtime.mPark () at /usr/local/go/src/runtime/proc.go:1441
#4  0x00000000004462d8 in runtime.stopm () at /usr/local/go/src/runtime/proc.go:2408
#5  0x00000000004477a5 in runtime.findrunnable () at /usr/local/go/src/runtime/proc.go:2984
#6  0x00000000004486d9 in runtime.schedule () at /usr/local/go/src/runtime/proc.go:3367
#7  0x0000000000448c2d in runtime.park_m (gp=0xc0000011e0) at /usr/local/go/src/runtime/proc.go:3516
#8  0x00000000004704c3 in runtime.mcall () at /usr/local/go/src/runtime/asm_amd64.s:307
#9  0xf934f160b63ffd00 in ?? ()
#10 0x0000000000800000 in text/template/parse.(*lexer).errorf (l=0x0, format=..., args=...) at /usr/local/go/src/text/template/parse/lex.go:188
#11 text/template/parse.lexComment (l=0x0) at /usr/local/go/src/text/template/parse/lex.go:319
#12 0x0000000000000000 in ?? ()

Thread 3 (LWP 1904479 "godal.test"):
#0  runtime.futex () at /usr/local/go/src/runtime/sys_linux_amd64.s:520
#1  0x000000000043b6f6 in runtime.futexsleep (addr=0xfffffffffffffe00, val=2, ns=4670691) at /usr/local/go/src/runtime/os_linux.go:44
#2  0x00000000004155f9 in runtime.lock2 (l=0xfffffffffffffe00) at /usr/local/go/src/runtime/lock_futex.go:107
#3  0x000000000040f55a in runtime.lockWithRank (l=0x4744e3 <runtime.futex+35>, rank=<optimized out>) at /usr/local/go/src/runtime/lockrank_off.go:23
#4  runtime.lock (l=0x4744e3 <runtime.futex+35>) at /usr/local/go/src/runtime/lock_futex.go:48
#5  runtime.chansend (c=0xc0001cd340, ep=0xc000406e4f, block=true, callerpc=<optimized out>) at /usr/local/go/src/runtime/chan.go:200
#6  0x000000000040f47d in runtime.chansend1 (c=0xfffffffffffffe00, elem=0x2) at /usr/local/go/src/runtime/chan.go:143
#7  0x00000000005139e8 in testing.tRunner.func1.1 () at /usr/local/go/src/testing/testing.go:1189
#8  0x00000000005134e7 in testing.tRunner.func1 () at /usr/local/go/src/testing/testing.go:1250
#9  0x000000000051317b in testing.tRunner (t=0xc0003b41a0, fn={void (testing.T *)} 0xc000406fc8) at /usr/local/go/src/testing/testing.go:1265
#10 0x0000000000513e4a in testing.(*T).Run·dwrap·21 () at /usr/local/go/src/testing/testing.go:1306
#11 0x0000000000472701 in runtime.goexit () at /usr/local/go/src/runtime/asm_amd64.s:1581
--Type <RET> for more, q to quit, c to continue without paging--
#12 0x0000000000000000 in ?? ()

Thread 2 (LWP 1904478 "godal.test"):
#0  runtime.usleep () at /usr/local/go/src/runtime/sys_linux_amd64.s:146
#1  0x000000000044d2d1 in runtime.sysmon () at /usr/local/go/src/runtime/proc.go:5337
#2  0x0000000000444c93 in runtime.mstart1 () at /usr/local/go/src/runtime/proc.go:1407
#3  0x0000000000444bd9 in runtime.mstart0 () at /usr/local/go/src/runtime/proc.go:1365
#4  0x0000000000470445 in runtime.mstart () at /usr/local/go/src/runtime/asm_amd64.s:248
#5  0x0000000000474b65 in runtime.mstart () at <autogenerated>:1
#6  0x00000000009d00b2 in crosscall_amd64 () at gcc_amd64.S:40
#7  0x00007fb871623640 in ?? ()
#8  0x0000000000000000 in ?? ()

Thread 1 (LWP 1904477 "godal.test"):
#0  runtime.futex () at /usr/local/go/src/runtime/sys_linux_amd64.s:520
#1  0x000000000043b6f6 in runtime.futexsleep (addr=0xfffffffffffffe00, val=2, ns=4670691) at /usr/local/go/src/runtime/os_linux.go:44
#2  0x00000000004155f9 in runtime.lock2 (l=0xfffffffffffffe00) at /usr/local/go/src/runtime/lock_futex.go:107
#3  0x0000000000410318 in runtime.lockWithRank (l=0x4744e3 <runtime.futex+35>, rank=<optimized out>) at /usr/local/go/src/runtime/lockrank_off.go:23
#4  runtime.lock (l=0x4744e3 <runtime.futex+35>) at /usr/local/go/src/runtime/lock_futex.go:48
#5  runtime.chanrecv (c=0xc0001cd340, ep=0xc00025fb67, block=true) at /usr/local/go/src/runtime/chan.go:508
#6  0x0000000000410198 in runtime.chanrecv1 (c=0xfffffffffffffe00, elem=0x2) at /usr/local/go/src/runtime/chan.go:439
#7  0x0000000000513d95 in testing.(*T).Run (t=0xc0003b41a0, name=..., f={void (testing.T *)} 0xc00025fbd8) at /usr/local/go/src/testing/testing.go:1307
#8  0x00000000005159ae in testing.runTests.func1 (t=0xc000283040) at /usr/local/go/src/testing/testing.go:1598
#9  0x0000000000513142 in testing.tRunner (t=0xc000283040, fn={void (testing.T *)} 0xc00025fc68) at /usr/local/go/src/testing/testing.go:1259
#10 0x000000000051585f in testing.runTests (matchString={void (string, string, bool *, error *)} 0xc00025fd10, tests=[]testing.InternalTest = {...}, deadline=...) at /usr/local/go/src/testing/testing.go:1596
--Type <RET> for more, q to quit, c to continue without paging--
#11 0x00000000005145bd in testing.(*M).Run (m=0xc00011c800, code=0) at /usr/local/go/src/testing/testing.go:1504
#12 0x00000000009ca56b in main.main () at _testmain.go:177
(gdb) q
A debugging session is active.

	Inferior 1 [process 1904477] will be detached.

Quit anyway? (y or n) y
Detaching from program: /home/tbonfort/dev/godal/godal.test, process 1904477
[Inferior 1 (process 1904477) detached]

I have bisected the issue down to 1c59066 (from @bcmills). Reverting this specific commit in master fixes the deadlock.

[bcmills]

@tbonfort, if you set -timeout=15s or similar you should get a goroutine dump from the Go runtime. Could you paste the full goroutine dump into a <details> block in a comment on this issue? The GDB backtrace appears to include only the subset of goroutines currently running on OS threads.

It isn't clear to me whether CL 303330 introduced a deadlock itself, exposed some other runtime bug (perhaps in defer and recover handling; compare #43941?) or exposed a latent bug in the test or one of the helper-libraries it uses. A full goroutine dump would help to determine which of those is the case.

[tbonfort]

@bcmills , sorry, I should have posted the go backtrace in the main issue. I didn't include it because it didn't contain any meaningful info for me aside of messages of the like of "goroutine running on other thread; stack unavailable". I'll post the exact output tomorrow UTC

[tbonfort]

Here is the dump:

panic: test timed out after 10s

goroutine 50 [running]:
testing.(*M).startAlarm.func1()
	/home/tbonfort/dev/thirdparty/go/src/testing/testing.go:1788 +0x8e
created by time.goFunc
	/home/tbonfort/dev/thirdparty/go/src/time/sleep.go:176 +0x32

goroutine 1 [running]:
	goroutine running on other thread; stack unavailable

goroutine 6 [select]:
go.opencensus.io/stats/view.(*worker).start(0xc0000fa280)
	/home/tbonfort/go/pkg/mod/go.opencensus.io@v0.23.0/stats/view/worker.go:276 +0xad
created by go.opencensus.io/stats/view.init.0
	/home/tbonfort/go/pkg/mod/go.opencensus.io@v0.23.0/stats/view/worker.go:34 +0x8d

goroutine 35 [running]:
	goroutine running on other thread; stack unavailable
created by testing.(*T).Run
	/home/tbonfort/dev/thirdparty/go/src/testing/testing.go:1306 +0x35f
exit status 2
FAIL	github.com/airbusgeo/godal	10.032s

[bcmills]

Yikes, that's not as helpful as I was hoping. 😞
Thanks anyway — I'll dig into it more from here!

[tbonfort]

Some additional info that may be useful:

• I had a cgo pointer passing rule that was not respected. Fixing it did not change the outcome of this issue, the hang happens at the same point. The test suite now runs cleanly with GODEBUG=cgocheck=2.
• I added a one-second sleep to all c functions called from cgo in order to force a gouroutine creation for all cgo calls (c.f. runtime: performance problem with many Cgo calls #19574 (comment)). The hang still happens at the same point.

[tbonfort]

Some more debugging info:

• using make(chan bool, 2) on t.signal does not modify the hanging behavior

• I added some fmt.Fprintf(os.Stderr, "START|DONE <- t.signal %p\n", t.signal) calls around the lines sending/receiving on t.signal, in t.Run and tRunner's defered func.
  On "working tests", I get

=== RUN   TestBandMask
START <- t.signal 0xc0000c21c0
--- PASS: TestBandMask (0.00s)
START: t.signal <- signal 0xc0000c21c0
DONE: t.signal <- signal 0xc0000c21c0
DONE <- t.signal 0xc0000c21c0

In the hanging case:

=== RUN   TestOpenShared
START <- t.signal 0xc0003a00e0
--- PASS: TestOpenShared (0.00s)
START: t.signal <- signal 0xc0003a00e0
DONE: t.signal <- signal 0xc0003a00e0
DONE <- t.signal 0xc0003a00e0
=== RUN   TestRegister
START <- t.signal 0xc0003a01c0
--- PASS: TestRegister (0.00s)
START: t.signal <- signal 0xc0003a01c0
/* hang */

Which seems strange as both goroutines seem to be blocking on read and write to the same channel.

• running the test suite under valgrind causes a hang with the same t.signal locking pattern, but in a subsequent test (i.e. a few tests after the TestRegister one). Outside of valgrind, the test suite consistently hangs right after TestRegister.

[toothrot]

Checking in on this issue, as it's labeled as a release blocker.