rocksdb.drop_table2 failed in buildbot, server crashed

rocksdb.drop_table2                      w4 [ fail ]  Found warnings/errors in server log file!

        Test ended at 2018-05-23 23:55:16

line

Attempting backtrace. You can use the following information to find out

^ Found warnings in /dev/shm/var/4/log/mysqld.1.err

ok

 - found 'core.11797' (0/0)

Trying 'dbx' to get a backtrace

gdb not found, cannot get the stack trace

Trying 'lldb' to get a backtrace from coredump /dev/shm/var/4/log/rocksdb.drop_table2/mysqld.1/data/core.11797

Compressed file /dev/shm/var/4/log/rocksdb.drop_table2/mysqld.1/data/core.11797

 - saving '/dev/shm/var/4/log/rocksdb.drop_table2/' to '/dev/shm/var/log/rocksdb.drop_table2/'