os: Readdirnames throws errors on CIFS

[rfjakob]

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

$ go version
go version go1.14.3 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/jakob/.cache/go-build"
GOENV="/home/jakob/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/jakob/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"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/jakob/go/src/github.com/rfjakob/gocryptfs/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 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build655782218=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Run readdirnames.go against a cifs mount:

while sleep 1 ; do ./readdirnames /mnt/synology/public/tmp/g1 ; done

Mount info:

//192.168.0.3/public on /mnt/synology/public type cifs (rw,relatime,vers=3.1.1,cache=strict,username=jakob,uid=1026,forceuid,gid=1026,forcegid,addr=192.168.0.3,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,rsize=4194304,wsize=4194304,bsize=1048576,echo_interval=60,actimeo=1)

Linux kernel:

5.6.13-300.fc32.x86_64

What did you expect to see?

No errors, consistent results, like from the C program getdents.c

$ while sleep 1 ; do ./getdents_c /mnt/synology/public/tmp/g1 ; done
getdents64 fd3: n=4176, errno=0
getdents64 fd3: n=4176, errno=0
getdents64 fd3: n=4176, errno=0
getdents64 fd3: n=4176, errno=0
getdents64 fd3: n=4176, errno=0
getdents64 fd3: n=3192, errno=0
getdents64 fd3: n=0, errno=0
total 24072 bytes

[repeats ad infinitum]

What did you see instead?

readdirnames.go :

$ while sleep 1 ; do ./readdirnames /mnt/synology/public/tmp/g1 ; done
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=694, err=readdirent: no such file or directory
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=346, err=readdirent: no such file or directory
Readdirnames: len=1001, err=<nil>
Readdirnames: len=346, err=readdirent: no such file or directory
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=346, err=readdirent: no such file or directory
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=520, err=readdirent: no such file or directory
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=694, err=readdirent: no such file or directory
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
2020/05/24 23:59:25 os.Open returned err=open /mnt/synology/public/tmp/g1: interrupted system call
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>

The problem is easier to trigger when the terminal window is continously resized (this triggers SIGWINCH signals).

This is problably the same underlying issue as in #24015 , and I agree that it looks like a kernel bug.

However, the C program seems to handle this fine, even with window resizing stress. So if glibc has workarounds for this, maybe Go should have them as well.

Downstream issue: rfjakob/gocryptfs#483

[ianlancetaylor]

This seems like the same issue as #38836. Is it possible for you to check whether the problem is fixed on master? Thanks.

[rfjakob]

Yes can do. Looks the same on master:

$ go build
$ go version
go version devel +f65ad0dda7 Sun May 24 20:49:55 2020 +0000 linux/amd64
$ while sleep 1 ; do ./readdirnames /mnt/synology/public/tmp/g1 ; done
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
2020/05/25 08:20:36 os.Open returned err=open /mnt/synology/public/tmp/g1: interrupted system call
Readdirnames: len=172, err=readdirent: no such file or directory
Readdirnames: len=868, err=readdirent: no such file or directory
Readdirnames: len=346, err=readdirent: no such file or directory
Readdirnames: len=346, err=readdirent: no such file or directory
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
Readdirnames: len=1001, err=<nil>
^C

[rfjakob]

I posted a summary of the issue to linux-cifs and linux-kernel a few day ago:
https://lore.kernel.org/linux-cifs/2d735cb666872099b2c4c574e35aaeac2f7356ad.camel@gmail.com/

No reply yet, but I'm pretty sure now that this is a kernel bug. Does it make sense to keep this ticket open for tracking the issue?

[networkimprov]

@gopherbot remove WaitingForInfo

[gopherbot]

Change https://golang.org/cl/236997 mentions this issue: os: always check for EINTR in calls to open

[ianlancetaylor]

I'm going to add a check for EINTR in calls to open. I think that should fix the problem with Go.

[rfjakob]

Nice, that should fix the open problem. The ENOENT in the middle of readdirent is tricky, though.

Readdirnames: len=868, err=readdirent: no such file or directory

[ianlancetaylor]

Quite right, sorry, it will only fix the problem with os.Open. I don't know what to do with the readdirent problem, but it sounds like that is a kernel bug, and not something we can avoid in Go. So I'm going to close this issue now. Please comment if you disagree.