Dep: Panic (maybe a race?) when `init` on kops

[kris-nova]

Trying to play with dep + kops (again) today!

Anyway just hit this weird panic where I had to manually remove the lockfile to try again. (Note, that dep init worked on the second try!)

kris-nova:kops kris$ dep init
Cached github.com/golang/glog
Cached github.com/kr/pty
Cached github.com/spf13/pflag
Cached github.com/docker/engine-api
Cached github.com/blang/semver
Cached github.com/gucumber/gucumber
Cached github.com/docker/libnetwork
Cached k8s.io/gengo
Cached github.com/opencontainers/runc
Cached k8s.io/client-go
Cached github.com/gogo/protobuf
Cached github.com/google/cadvisor
Cached github.com/coreos/rkt
Cached github.com/aws/aws-sdk-go
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x50 pc=0xda270]

goroutine 181 [running]:
panic(0x3a6380, 0xc4200100d0)
    /usr/local/Cellar/go/1.7.5/libexec/src/runtime/panic.go:500 +0x1a1
github.com/golang/dep/vendor/github.com/sdboyer/gps.(*SourceMgr).SyncSourceFor(0xc42008e000, 0xc4206f80c0, 0x13, 0x0, 0x0, 0x0, 0x0)
    /go/src/github.com/golang/dep/vendor/github.com/sdboyer/gps/source_manager.go:461 +0x180
main.getProjectData.func1(0xc4206f80c0, 0x13, 0xc42008e000)
    /go/src/github.com/golang/dep/cmd/dep/init.go:244 +0x6c
created by main.getProjectData
    /go/src/github.com/golang/dep/cmd/dep/init.go:279 +0xdf3
kris-nova:kops kris$ dep init
getSourceManager: cache lock file /go/pkg/dep/sm.lock exists - another process crashed or is still running?
kris-nova:kops kris$ rm -rf /go/pkg/dep/sm.lock 
kris-nova:kops kris$ dep init

# Working init logs here

[sdboyer]

Hmm, this must be an oversight in how we modified dep init to prefetch information in #194. Looks like some version of use-after-free...

[davecheney]

Lock files on disk :(

On Sun, Feb 19, 2017 at 3:25 AM, sam boyer [e-mail] wrote:

Hmm, this must be an oversight in how we modified dep init to prefetch
information in #194 https://github.com/golang/dep/pull/194. Looks like
some version of use-after-free...

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[sdboyer]

254 is a dupe of this, but it shows the underlying problem isn't the changes we made in init - there's a bug in gps.

[sdboyer]

Lock files on disk :(

@davecheney agree 😢 suggestions welcome! (in another issue - should actually be a gps issue)

[sdboyer]

Should be fixed upstream - variable shadowing issue. sdboyer/gps#187

[doxxx]

I just tested the sdboyer/gps#187 fix by running dep ensure -update github.com/sdboyer/gps in my $GOPATH/src/github.com/golang/dep folder and then go install. After that I was able to use dep init and various dep ensure commands on a project which prior to this was causing this panic every time.