Fix deadlock in consumer group handleError

[matthewloring]

The deadlock can happen if the heartbeat request runs out of retries while the consumer group session is being released. consumerGroup.Consume will acquire the consumer group lock and then call consumerGroupSession.release which will block waiting for the channel hbDead to be closed. If the heartbeatLoop then runs out of retries and calls consumerGroup.handleError the handleError call will block on the lock preventing heartbeatLoop from closing hbDead.

It is safe to remove the lock acquisition in handleError because the channel operations in the critical section are already thread safe.

I also moved the lock/unlock from Close into leave to more accurately reflect the resources being protected.

Example stack traces for the deadlock:

goroutine 1 [semacquire, 2 minutes]:
sync.runtime_SemacquireMutex(0xc00131aa74, 0xc0010b5500, 0x1)
        /usr/local/Cellar/go/1.13.3/libexec/src/runtime/sema.go:71 +0x47
sync.(*Mutex).lockSlow(0xc00131aa70)
        /usr/local/Cellar/go/1.13.3/libexec/src/sync/mutex.go:138 +0xfc
sync.(*Mutex).Lock(...)
        /usr/local/Cellar/go/1.13.3/libexec/src/sync/mutex.go:81
github.com/Shopify/sarama.(*consumerGroup).Close.func1()
        /Users/<redacted>/go/pkg/mod/github.com/!shopify/sarama@v1.25.0/consumer_group.go:123 +0x1f0
sync.(*Once).doSlow(0xc00131aa80, 0xc0045fb7c8)
        /usr/local/Cellar/go/1.13.3/libexec/src/sync/once.go:66 +0xe3
sync.(*Once).Do(...)
        /usr/local/Cellar/go/1.13.3/libexec/src/sync/once.go:57
github.com/Shopify/sarama.(*consumerGroup).Close(0xc00131aa20, 0x0, 0x0)
        /Users/<redacted>/go/pkg/mod/github.com/!shopify/sarama@v1.25.0/consumer_group.go:120 +0x7d
...

goroutine 468 [chan receive, 10 minutes]:
github.com/Shopify/sarama.(*consumerGroupSession).release.func1()
        /Users/<redacted>/go/pkg/mod/github.com/!shopify/sarama@v1.25.0/consumer_group.go:719 +0x97
sync.(*Once).doSlow(0xc0012f2664, 0xc0018f6d38)
        /usr/local/Cellar/go/1.13.3/libexec/src/sync/once.go:66 +0xe3
sync.(*Once).Do(...)
        /usr/local/Cellar/go/1.13.3/libexec/src/sync/once.go:57
github.com/Shopify/sarama.(*consumerGroupSession).release(0xc0012f2600, 0x1, 0x0, 0x0)
        /Users/<redacted>/go/pkg/mod/github.com/!shopify/sarama@v1.25.0/consumer_group.go:706 +0xb0
github.com/Shopify/sarama.(*consumerGroup).Consume(0xc00131aa20, 0x662ef60, 0xc000225580, 0xc0013c6f10, 0x1, 0x1, 0x66231a0, 0xc0007e37e0, 0x0, 0x0)
        /Users/<redacted>/go/pkg/mod/github.com/!shopify/sarama@v1.25.0/consumer_group.go:184 +0x27d
...

goroutine 956 [semacquire, 10 minutes]:
sync.runtime_SemacquireMutex(0xc00131aa74, 0xc000149f00, 0x1)
        /usr/local/Cellar/go/1.13.3/libexec/src/runtime/sema.go:71 +0x47
sync.(*Mutex).lockSlow(0xc00131aa70)
        /usr/local/Cellar/go/1.13.3/libexec/src/sync/mutex.go:138 +0xfc
sync.(*Mutex).Lock(...)
        /usr/local/Cellar/go/1.13.3/libexec/src/sync/mutex.go:81
github.com/Shopify/sarama.(*consumerGroup).handleError(0xc00131aa20, 0x65fa680, 0xc0072ff860, 0xc0012b9bc0, 0xc, 0xc000000000)
        /Users/<redacted>/go/pkg/mod/github.com/!shopify/sarama@v1.25.0/consumer_group.go:433 +0x175
github.com/Shopify/sarama.newConsumerGroupClaim.func1(0x6639e20, 0xc001114dc0, 0xc0012f2600, 0xc0012b9bc0, 0xc, 0x0)
        /Users/<redacted>/go/pkg/mod/github.com/!shopify/sarama@v1.25.0/consumer_group.go:846 +0x96
created by github.com/Shopify/sarama.newConsumerGroupClaim
        /Users/<redacted>/go/pkg/mod/github.com/!shopify/sarama@v1.25.0/consumer_group.go:844 +0x10d

[dnwe]

@matthewloring these changes look reasonable — are you able to sign the cla?

[matthewloring]

I already have. I didn't have permission to re-run the ci after signing.

[dnwe]

@matthewloring ah OK — it should re-run checks if you click on the Close pull request button and then immediately click on the Re-open pull request button straight after

[matthewloring]

That started the travis CI but not the CLA check

[matthewloring]

Anything else I can do to re-run the CLA bot?

[dnwe]

The quickest solution is probably just to close this PR and re-open with a new PR and just paste the description across.

Otherwise you'd have to chase one of the Shopify guys (@eapache / @d1egoaz), but its probably quicker to just try re-spinning a new PR

[d1egoaz]

I've re-run the CLA check

[d1egoaz]

ping @bai @varun06 👀

[bai]

PR looks good to me. I’m away for the rest of the week, please feel free to merge at will. 🙏