memcached segfault from pruneXattrDocument

Core was generated by `/opt/couchbase/bin/memcached -C /opt/couchbase/var/lib/couchbase/config/memcach'.

#0 vlength (this=<optimized out>, this=<optimized out>)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/engines/ep/src/blob.h:124

Thread 1 (LWP 26987):

#0 vlength (this=<optimized out>, this=<optimized out>)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/engines/ep/src/blob.h:124

#1 VBucket::pruneXattrDocument (this=this@entry=0x7f45c85bbe00, v=..., itemMeta=...)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/engines/ep/src/vbucket.cc:2500

#2 0x00007f4622338382 in VBucket::deleteWithMeta (this=0x7f45c85bbe00, key=..., cas=@0x7f46195d26a0: 0, 

seqno=seqno@entry=0x7f46195d26c0, cookie=cookie@entry=0x7f461529d118, engine=..., bgFetchDelay=0, 

checkConflicts=checkConflicts@entry=Yes, itemMeta=..., backfill=backfill@entry=false, genBySeqno=genBySeqno@entry=Yes, 

generateCas=generateCas@entry=No, bySeqno=bySeqno@entry=0, isReplication=isReplication@entry=false)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/engines/ep/src/vbucket.cc:1354

#3 0x00007f462230967e in KVBucket::deleteWithMeta (this=0x7f461024e000, key=..., cas=@0x7f46195d26a0: 0, seqno=0x7f46195d26c0, 

vbucket=<optimized out>, cookie=0x7f461529d118, permittedVBStates=..., checkConflicts=Yes, itemMeta=..., backfill=false, 

genBySeqno=Yes, generateCas=No, bySeqno=0, emd=0x0, isReplication=false)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/engines/ep/src/kv_bucket.cc:1883

#4 0x00007f46222c1fa4 in EventuallyPersistentEngine::deleteWithMeta (this=this@entry=0x7f4624d89800, vbucket=vbucket@entry=213, 

key=..., itemMeta=..., cas=@0x7f46195d26a0: 0, seqno=seqno@entry=0x7f46195d26c0, cookie=cookie@entry=0x7f461529d118, 

permittedVBStates=..., checkConflicts=Yes, genBySeqno=genBySeqno@entry=Yes, genCas=No, emd=...)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/engines/ep/src/ep_engine.cc:4569

#5 0x00007f46222cad8a in EventuallyPersistentEngine::deleteWithMeta (this=this@entry=0x7f4624d89800, 

cookie=cookie@entry=0x7f461529d118, request=request@entry=0x7f43c3a1e5e9, response=response@entry=

0x485ba0 <mcbp_response_handler(void const*, unsigned short, void const*, unsigned char, void const*, unsigned int, unsigned char, unsigned short, unsigned long, void const*)>, docNamespace=docNamespace@entry=DefaultCollection)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/engines/ep/src/ep_engine.cc:4500

#6 0x00007f46222d17b4 in processUnknownCommand (docNamespace=DefaultCollection, 

response=0x485ba0 <mcbp_response_handler(void const*, unsigned short, void const*, unsigned char, void const*, unsigned int, unsigned char, unsigned short, unsigned long, void const*)>, request=0x7f43c3a1e5e9, cookie=0x7f461529d118, h=0x7f4624d89800)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/engines/ep/src/ep_engine.cc:1173

#7 EvpUnknownCommand (handle=0x7f4624d89800, cookie=0x7f461529d118, request=0x7f43c3a1e5e9, 

response=0x485ba0 <mcbp_response_handler(void const*, unsigned short, void const*, unsigned char, void const*, unsigned int, unsigned char, unsigned short, unsigned long, void const*)>, doc_namespace=<optimized out>)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/engines/ep/src/ep_engine.cc:1270

#8 0x000000000042065c in bucket_unknown_command (c=0x7f461529ce00, request=request@entry=0x7f43c3a1e5e9, 

response=response@entry=0x485ba0 <mcbp_response_handler(void const*, unsigned short, void const*, unsigned char, void const*, unsigned int, unsigned char, unsigned short, unsigned long, void const*)>)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/daemon/protocol/mcbp/engine_wrapper.cc:28

#9 0x000000000044e5f4 in default_unknown_command (void_cookie=<optimized out>, request=0x7f43c3a1e5e9, 

response=0x485ba0 <mcbp_response_handler(void const*, unsigned short, void const*, unsigned char, void const*, unsigned int, unsigned char, unsigned short, unsigned long, void const*)>)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/daemon/mcbp_executors.cc:204

#10 0x0000000000453a58 in process_bin_unknown_packet (packet=0x7f43c3a1e5e9, c=0x7f461529ce00)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/daemon/mcbp_executors.cc:241

#11 execute_request_packet (c=0x7f461529ce00)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/daemon/mcbp_executors.cc:1372

#12 mcbp_complete_packet (c=c@entry=0x7f461529ce00)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/daemon/mcbp_executors.cc:1483

#13 0x0000000000474e8f in conn_execute (c=0x7f461529ce00)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/daemon/statemachine_mcbp.cc:306

#14 0x0000000000441d38 in execute (connection=..., this=<optimized out>)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/daemon/statemachine_mcbp.h:43

#15 McbpConnection::runStateMachinery (this=0x7f461529ce00)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/daemon/connection_mcbp.cc:870

#16 0x0000000000441d7b in McbpConnection::runEventLoop (this=0x7f461529ce00, which=-16896)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/daemon/connection_mcbp.cc:1169

#17 0x00000000004459ae in run_event_loop (c=0x7f461529ce00, which=<optimized out>)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/daemon/connections.cc:146

#18 0x00000000004309f6 in thread_libevent_process (fd=<optimized out>, which=<optimized out>, arg=0x7f4624d82f78)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/daemon/thread.cc:337

#19 0x00007f46280d47ec in event_process_active_single_queue.isra.26 () from /opt/couchbase/lib/libevent_core.so.2.1.8

#20 0x00007f46280d7c3f in event_base_loop () from /opt/couchbase/lib/libevent_core.so.2.1.8

#21 0x0000000000430524 in worker_libevent (arg=0x7f4624d82f78)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/kv_engine/daemon/thread.cc:233

#22 0x00007f4628fb40ae in run (this=0x7f4624d2fbe0)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/platform/src/cb_pthreads.cc:59

#23 platform_thread_wrap (arg=0x7f4624d2fbe0)

at /home/couchbase/jenkins/workspace/couchbase-server-unix/platform/src/cb_pthreads.cc:72

#24 0x00007f4628974dc5 in start_thread () from /usr/lib64/libpthread-2.17.so

#25 0x00007f4626b2428d in clone () from /usr/lib64/libc-2.17.so