slapd strange backtrace

slapd gdb

(gdb) bt
#0  0x00007f2b8ca6e2e3 in epoll_wait () from /lib64/libc.so.6
#1  0x00007f2b8f4ba354 in slapd_daemon_task (ptr=<optimized out>) at daemon.c:2536
#2  0x00007f2b8e42d7b6 in start_thread () from /lib64/libpthread.so.0
#3  0x00007f2b8ca6dc5d in clone () from /lib64/libc.so.6
#4  0x0000000000000000 in ?? ()
(gdb)