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os/exec: incorrect "fatal error: all goroutines are asleep - deadlock!" #41271

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martinrode opened this issue Sep 8, 2020 · 4 comments
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os/exec: incorrect "fatal error: all goroutines are asleep - deadlock!" #41271

martinrode opened this issue Sep 8, 2020 · 4 comments
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FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
Milestone
Go1.16

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

$ go version
go version go1.15 darwin/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="on"
GOARCH="amd64"
GOBIN="/Users/martin/go/bin"
GOCACHE="/Users/martin/Library/Caches/go-build"
GOENV="/Users/martin/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/martin/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/martin/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/martin/go/src/github.com/programmfabrik/fylr/go.mod"
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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/4f/l31kb4n521d6g89qxrwcx69h0000gp/T/go-build343164864=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Playground

package main

import (
	"context"
	"io"
	"os/exec"
	"time"
)

func main() {
	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
	defer cancel()
	cmd := exec.CommandContext(ctx, "sleep", "2")
	cmd.Stdin, _ = io.Pipe() // This prevents the "Timeout" to work correctly
	cmd.Run()                // Wrongly gets killed with "deadlock" detected
}

What did you expect to see?

I expect my program to not deadlock, but instead kill "sleep" and return from "Run" with an error. The unclosed STDIN should not prevent the program from returning.

Related or DUP?

Issue #23019 might be related to this?

What did you see instead?

The program deadlocks which is not what I expect.
@fatelei
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fatelei commented Sep 8, 2020

In golang, the deadlock is detected when there is only main goroutine running

@martinrode
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In golang, the deadlock is detected when there is only main goroutine running

Nope, comment the cmd.Stdin line, and see how the program works.

@andybons
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andybons commented Sep 8, 2020

@bradfitz @ianlancetaylor

@andybons andybons added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Sep 8, 2020
@andybons andybons added this to the Unplanned milestone Sep 8, 2020
@ianlancetaylor ianlancetaylor changed the title os/exec: Timeout (and unclosed Stdin) not working correctly runtime: incorrect "fatal error: all goroutines are asleep - deadlock!" Sep 8, 2020
@ianlancetaylor ianlancetaylor modified the milestones: Unplanned, Go1.16 Sep 8, 2020
@ianlancetaylor ianlancetaylor changed the title runtime: incorrect "fatal error: all goroutines are asleep - deadlock!" os/exec: incorrect "fatal error: all goroutines are asleep - deadlock!" Sep 8, 2020
@ianlancetaylor
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This is an interesting case. It's related to #23019, certainly. Because you used io.Pipe rather than, say, os.Pipe, the Go runtime knows for sure that nothing is ever going to write to that pipe. So the os/exec package is waiting for something to write to the pipe, and the runtime knows that that will never happen. So the runtime is correctly reporting a deadlock.

I'm going to close this as a dup of #23019, because if we fix that problem, we will fix this one. And if we don't fix that problem, then I don't think there is anything we can do about this one.

@golang golang locked and limited conversation to collaborators Sep 8, 2021
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@andybons @fatelei @ianlancetaylor @gopherbot @martinrode