Ceph librbd: thread_pool worker queue crash in void *item = wq->_void_dequeue()

Issue

• Ceph librbd: thread_pool worker queue crash in void *item = wq->_void_dequeue()
• nova-compute randomly segfaults when librbd in use

Core was generated by `/usr/bin/python2 /usr/bin/nova-compute --config-file /etc/nova/nova.conf --conf'.
Program terminated with signal 11, Segmentation fault.
#0  ThreadPool::worker (this=0x726e5a0, wt=0x2d9a4f0) at common/WorkQueue.cc:120
120     void *item = wq->_void_dequeue();

(gdb) bt
#0  ThreadPool::worker (this=0x726e5a0, wt=0x2d9a4f0) at common/WorkQueue.cc:120
#1  0x00007f1e59b614d0 in ThreadPool::WorkThread::entry (this=) at common/WorkQueue.h:318
#2  0x00007f1ef0abedc5 in start_thread (arg=0x7f1e599fa700) at pthread_create.c:308
#3  0x00007f1ef00e31cd in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:113

• Some times with below given back trace:

#0  0x00007f0ca7b7620b in raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/pt-raise.c:37
#1  0x00007f0cad50192d in reraise_fatal (signum=6) at global/signal_handler.cc:59
#2  handle_fatal_signal (signum=6) at global/signal_handler.cc:109
#3  <signal handler called>
#4  0x00007f0ca6634cc9 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
#5  0x00007f0ca66380d8 in __GI_abort () at abort.c:89
#6  0x00007f0ca6f3f535 in __gnu_cxx::__verbose_terminate_handler() () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#7  0x00007f0ca6f3d6d6 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#8  0x00007f0ca6f3d703 in std::terminate() () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#9  0x00007f0ca6f3e1bf in __cxa_pure_virtual () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#10 0x00007f0caa7acfe4 in ThreadPool::WorkQueueVal<std::pair<Context*, int>, std::pair<Context*, int> >::_void_dequeue (
    this=0x7f0cb09d6360) at ./common/WorkQueue.h:197
#11 0x00007f0caa8aae84 in ThreadPool::worker (this=0x7f0cb09cfdf0, wt=0x7f0cb09c1970) at common/WorkQueue.cc:120
#12 0x00007f0caa8ac220 in ThreadPool::WorkThread::entry (this=<optimized out>) at common/WorkQueue.h:362
#13 0x00007f0ca7b6e182 in start_thread (arg=0x7f0c9a7fc700) at pthread_create.c:312
#14 0x00007f0ca66f847d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111