Here it is!
I copied the core file and the corresponding log file (from ccqserv124) to
/nfs/lsst/db1/xrdFromIN2P3 at slac.
The stack trace:
Program terminated with signal 11, Segmentation fault.
#0 0x00007f6791f10c10 in pthread_mutex_lock () from /lib64/libpthread.so.0
Missing separate debuginfos, use: debuginfo-install expat-2.1.0-8.el7.x86_64 glibc-2.17-78.el7.x86_64 keyutils-libs-1.5.8-3.el7.x86_64 krb5-libs-1.12.2-14.el7.x86_64 libcom_err-1.42.9-7.el7.x86_64 libgcc-4.8.3-9.el7.x86_64 libicu-50.1.2-11.el7.x86_64 libselinux-2.2.2-6.el7.x86_64 libstdc++-4.8.3-9.el7.x86_64 nss-softokn-freebl-3.16.2.3-9.el7.x86_64 openssl-libs-1.0.1e-42.el7_1.9.x86_64 pcre-8.32-14.el7.x86_64 xz-libs-5.1.2-9alpha.el7.x86_64 zlib-1.2.7-13.el7.x86_64
(gdb) where
#0 0x00007f6791f10c10 in pthread_mutex_lock () from /lib64/libpthread.so.0
#1 0x00007f678ba68b1e in XrdSsiMutex::Lock (this=0x39382e31343a3652)
#2 0x00007f678ba6d9f8 in XrdSsiResponder::SetResponse (this=0x7f677c048ea8, strmP=0x7f676401c4f0)
#3 0x00007f678ba6d649 in lsst::qserv::xrdsvc::SsiSession::ReplyChannel::_initStream (this=0x7f674801ff68)
at build/xrdsvc/SsiSession_ReplyChannel.cc:99
#4 0x00007f678ba6d579 in lsst::qserv::xrdsvc::SsiSession::ReplyChannel::sendStream (this=0x7f674801ff68,
buf=0x7f676401b2b8 "(\r\002", bufLen=256, last=false) at build/xrdsvc/SsiSession_ReplyChannel.cc:87
#5 0x00007f678ba31c39 in lsst::qserv::wdb::QueryAction::Impl::_transmitHeader (this=0x7f676401a380,
msg="\b\000\020\001\032\035\n\033\n\tQS1_COUNT\020\000\"\nBIGINT(21)(\b2\005\n\001\060\020")
#6 0x00007f678ba31672 in lsst::qserv::wdb::QueryAction::Impl::_transmit (this=0x7f676401a380, last=true)
#7 0x00007f678ba31f5b in lsst::qserv::wdb::QueryAction::Impl::_dispatchChannel (this=0x7f676401a380)
#8 0x00007f678ba305ab in lsst::qserv::wdb::QueryAction::Impl::act (this=0x7f676401a380)
#9 0x00007f678ba33084 in lsst::qserv::wdb::QueryAction::operator() (this=0x7f6764000a78)
#10 0x00007f678ba15f46 in lsst::qserv::wcontrol::ForemanImpl::Runner::operator() (this=0x7f674c097db0)