inconsistent locking order

[marten-seemann]

Running our test suite with https://github.com/sasha-s/go-deadlock yields the following potential deadlock:

=== RUN   TestCloseRead
POTENTIAL DEADLOCK: Inconsistent locking. saw this ordering in one goroutine:
happened before
stream.go:396 v3.(*Stream).processFlags { s.stateLock.Lock() } <<<<<
stream.go:395 v3.(*Stream).processFlags {  }
stream.go:437 v3.(*Stream).incrSendWindow { // Increase window, unblock a sender }
session.go:706 v3.(*Session).handleStreamMessage { stream.incrSendWindow(hdr, flags) }
session.go:666 v3.(*Session).recvLoop {  }
session.go:614 v3.(*Session).recv { func (s *Session) recv() { }

happened after
session.go:865 v3.(*Session).establishStream { s.streamLock.Lock() } <<<<<
session.go:864 v3.(*Session).establishStream { func (s *Session) establishStream(id uint32) { }
stream.go:403 v3.(*Stream).processFlags { } }
stream.go:437 v3.(*Stream).incrSendWindow { // Increase window, unblock a sender }
session.go:706 v3.(*Session).handleStreamMessage { stream.incrSendWindow(hdr, flags) }
session.go:666 v3.(*Session).recvLoop {  }
session.go:614 v3.(*Session).recv { func (s *Session) recv() { }

in another goroutine: happened before
session.go:294 v3.(*Session).Close { s.streamLock.Lock() } <<<<<
session.go:293 v3.(*Session).Close {  }
session.go:316 v3.(*Session).exitErr { s.Close() }
session.go:489 v3.(*Session).send { } }

happened after
stream.go:363 v3.(*Stream).forceClose { s.stateLock.Lock() } <<<<<
stream.go:362 v3.(*Stream).forceClose { func (s *Stream) forceClose() { }
session.go:299 v3.(*Session).Close { stream.forceClose() }
session.go:316 v3.(*Session).exitErr { s.Close() }
session.go:489 v3.(*Session).send { } }

Other goroutines holding locks:
goroutine 3013287 lock 0xc0008d1888
session.go:278 v3.(*Session).Close { s.shutdownLock.Lock() } <<<<<
session.go:277 v3.(*Session).Close { func (s *Session) Close() error { }
session_test.go:841 v3.TestCloseRead { } }

goroutine 3013287 lock 0xc0008d1828
session.go:294 v3.(*Session).Close { s.streamLock.Lock() } <<<<<
session.go:293 v3.(*Session).Close {  }
session_test.go:841 v3.TestCloseRead { } }

goroutine 3013290 lock 0xc0008d1768
session.go:278 v3.(*Session).Close { s.shutdownLock.Lock() } <<<<<
session.go:277 v3.(*Session).Close { func (s *Session) Close() error { }
session.go:316 v3.(*Session).exitErr { s.Close() }
session.go:489 v3.(*Session).send { } }

goroutine 3013287 lock 0xc0165bc348
deadline.go:33 v3.(*pipeDeadline).set { d.mu.Lock() } <<<<<
deadline.go:32 v3.(*pipeDeadline).set { func (d *pipeDeadline) set(t time.Time) { }
stream.go:374 v3.(*Stream).forceClose { s.readDeadline.set(time.Time{}) }
session.go:299 v3.(*Session).Close { stream.forceClose() }
session_test.go:841 v3.TestCloseRead { } }

goroutine 3013290 lock 0xc0008d1708
session.go:294 v3.(*Session).Close { s.streamLock.Lock() } <<<<<
session.go:293 v3.(*Session).Close {  }
session.go:316 v3.(*Session).exitErr { s.Close() }
session.go:489 v3.(*Session).send { } }