openssl: OpenSSL 1.1.1 crash/hangs without thread usage

We have upgraded from OpenSSL 1.0.2k to OpenSSL 1.1.1(in linux) and see crashes/hangs occasionally. We also set externally created sessions and the crash/hang seems to happen during it’s reference counting operation. It’s not reproducible in unit tests. We did not disable threads even though it’s not used in the apps. Does openssl internally use thread even if app does not use it? we are considering to rebuild with no-threads since it’s not reproducible.

gdb Backtrace after an hang #0 0xffffe410 in __kernel_vsyscall () #1 0xf72ed839 in __lll_lock_wait () from /lib/libpthread.so.0 #2 0xf72ea452 in pthread_rwlock_wrlock () from /lib/libpthread.so.0 #3 0x083f972b in CRYPTO_THREAD_write_lock () #4 0x083f9716 in CRYPTO_THREAD_write_lock () #5 0x083f976a in CRYPTO_atomic_add ()