ep-engine crashed when reading data through UPR

Steps:
1. Single node
2. Load 10M x 2KB items (non-DGM), wait for persistence
3. Try to read all data through UPR

Result:
memcached crash

#0 0x0000003854832925 in raise () from /lib64/libc.so.6
#1 0x0000003854834105 in abort () from /lib64/libc.so.6
#2 0x00007fa5a35389d1 in cb_mutex_exit (mutex=<value optimized out>) at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/platform/src/cb_pthreads.c:103
#3 0x00007fa58cee0ee0 in unlock (this=0x1ecb5a80, itm=0x64fe89130) at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/ep-engine/src/locks.h:76
#4 ~LockHolder (this=0x1ecb5a80, itm=0x64fe89130) at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/ep-engine/src/locks.h:59
#5 ActiveStream::backfillReceived (this=0x1ecb5a80, itm=0x64fe89130) at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/ep-engine/src/upr-stream.cc:211
#6 0x00007fa58cee1214 in CacheCallback::callback (this=0x3c78b3280, lookup=...)
at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/ep-engine/src/upr-stream.cc:48
#7 0x00007fa58cf00c2b in CouchKVStore::recordDbDump (db=0x6c36a600, docinfo=0x6693e7f70, ctx=<value optimized out>)
at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/ep-engine/src/couch-kvstore/couch-kvstore.cc:1477
#8 0x00007fa58ca18490 in lookup_callback (rq=<value optimized out>, k=0x7fa560acd790, v=0x7fa560acd780)
at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/couchstore/src/couch_db.cc:721
#9 0x00007fa58ca169ed in btree_lookup_inner (rq=0x7fa560acd990, diskpos=<value optimized out>, current=0, end=1)
at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/couchstore/src/btree_read.cc:97
#10 0x00007fa58ca16b37 in btree_lookup_inner (rq=0x7fa560acd990, diskpos=<value optimized out>, current=0, end=1)
at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/couchstore/src/btree_read.cc:71
#11 0x00007fa58ca16b37 in btree_lookup_inner (rq=0x7fa560acd990, diskpos=<value optimized out>, current=0, end=1)
at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/couchstore/src/btree_read.cc:71
#12 0x00007fa58ca177af in couchstore_changes_since (db=0x6c36a600, since=<value optimized out>, options=<value optimized out>, callback=<value optimized out>,
ctx=<value optimized out>) at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/couchstore/src/couch_db.cc:764
#13 0x00007fa58cf074ac in CouchKVStore::loadDB (this=0x5a1b740, cb=std::tr1::shared_ptr (empty) 0x7fa560acdc60,
cl=std::tr1::shared_ptr (count 926299444) 0x7fa560acdc50, keysOnly=false, vbid=0, startSeqno=0, endSeqno=5000, options=0)
at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/ep-engine/src/couch-kvstore/couch-kvstore.cc:1161
#14 0x00007fa58cf0814c in CouchKVStore::dump (this=0x5a1b740, vb=0, stSeqno=0, enSeqno=5000, cb=std::tr1::shared_ptr (count 0) 0x7fa560acdd40,
cl=Traceback (most recent call last):
File "/usr/lib64/../share/gdb/python/libstdcxx/v6/printers.py", line 37, in to_string
self.val['_M_ptr'])
TypeError: %d format: a number is required, not gdb.Value
) at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/ep-engine/src/couch-kvstore/couch-kvstore.cc:1019
#15 0x00007fa58cedffb4 in UprBackfill::run (this=0x12d448210) at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/ep-engine/src/upr-stream.cc:102
#16 0x00007fa58ceadc99 in ExecutorThread::run (this=0x1149720) at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/ep-engine/src/executorthread.cc:93
#17 0x00007fa58ceae196 in launch_executor_thread (arg=0x25e7) at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/ep-engine/src/executorthread.cc:33
#18 0x00007fa5a3538b7f in platform_thread_wrap (arg=0x1139400) at /home/buildbot/centos-5-x64-300-builder/build/build/cmake/platform/src/cb_pthreads.c:19
#19 0x0000003854c079d1 in start_thread () from /lib64/libpthread.so.0
#20 0x00000038548e8b6d in clone () from /lib64/libc.so.6