MB-19278: Fix lock-order inversion on ActiveStream::streamMutex

ThreadSanitizer has identified a potential deadlock due to a cycle in
  the lock order graph: Cycle in lock order graph:

    M43515         => M36787      => M36848            => M43515
   [ActiveStream::   [TaskQueue::   [ExecutorThread::    [ActiveStream::
    streamMutex]      mutex]         currentTaskMutex]    streamMutex]

The crux of the problem appears to be the acquisition of streamMutex
in the destructor of ActiveStream. This is ultimately a Bad Idea - if
you still have multiple threads accessing an object when it's been
deleted then you are already into undefined behaviour.

Change-Id: I2353b5a8ed93a4f9e8cc036cb85680c185cbcc2f
Reviewed-on: http://review.couchbase.org/63033
Well-Formed: buildbot <build@couchbase.com>
Reviewed-by: Daniel Owen <owend@couchbase.com>
Tested-by: buildbot <build@couchbase.com>

diff --git a/src/dcp-stream.h b/src/dcp-stream.h
index 3623677..5461e97 100644 (file)
--- a/src/dcp-stream.h
+++ b/src/dcp-stream.h
@@ -174,7 +174,6 @@ public:
                  uint64_t snap_end_seqno);
 
     ~ActiveStream() {
-        LockHolder lh(streamMutex);
         transitionState(STREAM_DEAD);
         clear_UNLOCKED();
     }