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net/http/fcgi: deadlock during write (regression in 1.16beta1) #43901

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tdanecker opened this issue Jan 25, 2021 · 3 comments
Closed

net/http/fcgi: deadlock during write (regression in 1.16beta1) #43901

tdanecker opened this issue Jan 25, 2021 · 3 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done. release-blocker
Milestone
Go1.16

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@tdanecker
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tdanecker commented Jan 25, 2021 •
edited

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

$ go version
go version go1.16beta1 linux/amd64

Does this issue reproduce with the latest release?

This is a regression in 1.16beta1 introduced via https://go-review.googlesource.com/c/go/+/252417
It would be fixed by https://go-review.googlesource.com/c/go/+/275692

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

go env Output
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/root/.cache/go-build"
GOENV="/root/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/go"
GOPRIVATE=""
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="go1.16beta1"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/app/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=/tmp/go-build1261813594=/tmp/go-build -gno-record-gcc-switches"

What did you do?

When using fcgi behind nginx, writes to the ResponseWriter block because a mutex is still held by the goroutine serving the fcgi-child (https://github.com/golang/go/blob/master/src/net/http/fcgi/child.go#L174).

main.go:

package main

import (
	"fmt"
	"log"
	"net"
	"net/http"
	"net/http/fcgi"
)

func handler(w http.ResponseWriter, req *http.Request) {
	// the following write will block
	_, err := fmt.Fprintln(w, "test")
	if err != nil {
		log.Println(err)
	}
}

func main() {
	listener, err := net.Listen("tcp", ":9000")
	if err != nil {
		log.Fatalln(err)
	}
	err = fcgi.Serve(listener, http.HandlerFunc(handler))
	if err != nil {
		log.Fatalln(err)
	}
}

nginx.conf:

server {
    location / {
        include /etc/nginx/fastcgi.conf;
        fastcgi_pass localhost:9000;
    }
}

For a full, runnable example see fcgi_regression.zip

What did you expect to see?

$ curl localhost
test

What did you see instead?

$ curl localhost
<html>
<head><title>504 Gateway Time-out</title></head>
<body>
<center><h1>504 Gateway Time-out</h1></center>
<hr><center>nginx/1.19.6</center>
</body>
</html>

The server blocks and nginx returns a 504 Gateway Timeout after some time.
@bcmills bcmills added NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. release-blocker labels Jan 25, 2021
@bcmills bcmills added this to the Go1.16 milestone Jan 25, 2021
@bcmills
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bcmills commented Jan 25, 2021

CC @tz70s @odeke-em @bradfitz @golang/release

@odeke-em
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Thanks for the report @tdanecker, and thanks for the ping and triage @bcmills! It is too late in the cycle so I’ll lean towards a revert; my apologies for the regression.

@hillu hillu mentioned this issue Jan 25, 2021
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@gopherbot
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Change https://golang.org/cl/275692 mentions this issue: net/http/fcgi: remove locking added to prevent a test-only race

@dmitshur dmitshur added NeedsFix The path to resolution is known, but the work has not been done. and removed NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Jan 26, 2021
@golang golang locked and limited conversation to collaborators Jan 26, 2022
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Successfully merging a pull request may close this issue.

net/http/fcgi: remove locking added to prevent a test-only race hillu/go
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@dmitshur @odeke-em @bcmills @gopherbot @tdanecker