MB-34435: ActiveStream::setDead: Check for valid vb

Before attempting to remove any queued ACKs, check the vbucket is
valid - it may have already been deleted.

As detected by ASan:

==30588==ERROR: AddressSanitizer: SEGV on unknown address 0x0000000002f8 (pc 0x7fc1c437a4b6 bp 0x7fc1bfb35730 sp 0x7fc1bfb35500 T7)
==30588==The signal is caused by a READ memory access.
==30588==Hint: address points to the zero page.
    #0 0x7fc1c437a4b5 in std::__atomic_base<unsigned int>::load(std::memory_order) const /usr/local/include/c++/7.3.0/bits/atomic_base.h:396
    #1 0x7fc1c437a4b5 in bool folly::SharedMutexImpl<...>::lockSharedImpl<...::WaitForever&) build/tlm/deps/folly.exploded/include/folly/SharedMutex.h:1239
    #2 0x7fc1c437a4b5 in folly::SharedMutexImpl<...>::lock_shared() build/tlm/deps/folly.exploded/include/folly/SharedMutex.h:375
    #3 0x7fc1c437a4b5 in folly::SharedMutexImpl<...>::ReadHolder() build/tlm/deps/folly.exploded/include/folly/SharedMutex.h:1315
    #4 0x7fc1c437a4b5 in ActiveStream::setDead(end_stream_status_t) kv_engine/engines/ep/src/dcp/active_stream.cc:1135
    #5 0x7fc1c44a3f3a in operator() kv_engine/engines/ep/src/dcp/producer.cc:1489
    #6 0x7fc1c44a3f3a in for_each<...> /local/include/c++/7.3.0/bits/stl_algo.h:3884
    #7 0x7fc1c44a3f3a in DcpProducer::setDisconnect() kv_engine/engines/ep/src/dcp/producer.cc:1491
    #8 0x7fc1c4428f02 in DcpConnMap::disconnect(void const*) kv_engine/engines/ep/src/dcp/dcpconnmap.cc:316
    #9 0x7fc1c45897a0 in EventuallyPersistentEngine::handleDisconnect(void const*) kv_engine/engines/ep/src/ep_engine.cc:5792
    #10 0x7fc1c45897a0 in EvpHandleDisconnect kv_engine/engines/ep/src/ep_engine.cc:1682
    #11 0x447119 in perform_callbacks(ENGINE_EVENT_TYPE, void const*, void const*) kv_engine/daemon/memcached.cc:301
    #12 0x62cb94 in Connection::propagateDisconnect() const kv_engine/daemon/connection.cc:1506
    #13 0x62cb94 in Connection::close() kv_engine/daemon/connection.cc:1487
    #14 0x784fec in StateMachine::conn_pending_close() kv_engine/daemon/statemachine.cc:577
    #15 0x784fec in StateMachine::execute() kv_engine/daemon/statemachine.cc:129
    #16 0x63ccff in Connection::runStateMachinery() kv_engine/daemon/connection.cc:1312
    #17 0x63cfcb in Connection::runEventLoop(short) kv_engine/daemon/connection.cc:1386
    #18 0x681ab8 in run_event_loop(Connection*, short) kv_engine/daemon/connections.cc:147
    #19 0x45df77 in event_handler(int, short, void*) kv_engine/daemon/memcached.cc:855
    #20 0x7fc1ccc1f086 in event_persist_closure deps/packages/build/libevent/libevent-prefix/src/libevent/event.c:1580
    #21 0x7fc1ccc1f086 in event_process_active_single_queue deps/packages/build/libevent/libevent-prefix/src/libevent/event.c:1639
    #22 0x7fc1ccc1f5fe in event_process_active deps/packages/build/libevent/libevent-prefix/src/libevent/event.c:1738
    #23 0x7fc1ccc1f5fe in event_base_loop deps/packages/build/libevent/libevent-prefix/src/libevent/event.c:1961
    #24 0x5aa3df in worker_libevent kv_engine/daemon/thread.cc:218
    #25 0x7fc1cd4b8868 in CouchbaseThread::run() platform/src/cb_pthreads.cc:58
    #26 0x7fc1cd4b8868 in platform_thread_wrap platform/src/cb_pthreads.cc:71
    #27 0x7fc1cb35b6b9 in start_thread (/lib/x86_64-linux-gnu/libpthread.so.0+0x76b9)
    #28 0x7fc1cb09141c in clone (/lib/x86_64-linux-gnu/libc.so.6+0x10741c)

Change-Id: Ic806fdfa6aca458a0dc1b82f046bca76dcb75d40
Reviewed-on: http://review.couchbase.org/110054
Reviewed-by: Daniel Owen <[email protected]>
Tested-by: Dave Rigby <[email protected]>

engines/ep/src/dcp/active_stream.cc

@@ -1130,6 +1130,9 @@ uint32_t ActiveStream::setDead(end_stream_status_t status) {
     // (owned by a backfill) and clear a seqno ack from a new ActiveStream.
     if (supportSyncReplication()) {
         auto vb = engine->getVBucket(vb_);
+        if (!vb) {
+            return 0;
+        }
         // Take the vb state lock so that we don't change the state of
         // this vb
         folly::SharedMutex::ReadHolder vbStateLh(vb->getStateLock());