OpenStack instances backed by Ceph Block Devices (rbd) periodically crash with "Error in `/usr/libexec/qemu-kvm': invalid fastbin entry (free)" seen in instance-*.log files

Issue

• OpenStack instances backed by Ceph Block Devices (rbd) periodically crash via a segfault in qemu-kvm, the following can be found in instance-*.log files:

*** Error in `/usr/libexec/qemu-kvm': invalid fastbin entry (free): 0x00007f834436d5a0 ***
======= Backtrace: =========
/lib64/libc.so.6(+0x7d1fd)[0x7f85d71041fd]
/lib64/libnssutil3.so(SECITEM_FreeItem_Util+0x19)[0x7f85ddb3bc49]
/lib64/librados.so.2(+0x40c5aa)[0x7f85db4ab5aa]
/lib64/librados.so.2(_ZNK9CryptoKey7encryptEP11CephContextRKN4ceph6buffer4listERS4_RSs+0x70)[0x7f85db4a9c80]
/lib64/librados.so.2(_Z14encode_encryptIN4ceph6buffer4listEEiP11CephContextRKT_RK9CryptoKeyRS2_RSs+0x18c)[0x7f85db4a958c]
/lib64/librados.so.2(_ZN19CephxSessionHandler23check_message_signatureEP7Message+0x229)[0x7f85db4a7539]
/lib64/librados.so.2(_ZN4Pipe12read_messageEPP7MessageP18AuthSessionHandler+0x1f4e)[0x7f85db46113e]
/lib64/librados.so.2(_ZN4Pipe6readerEv+0xb9b)[0x7f85db472fcb]
/lib64/librados.so.2(_ZN4Pipe6Reader5entryEv+0xd)[0x7f85db47797d]
/lib64/libpthread.so.0(+0x7df5)[0x7f85dd2cbdf5]
/lib64/libc.so.6(clone+0x6d)[0x7f85d717d1ad]