...X PID: Y at kernel/rcutree.c:2221 rcu_process_callbacks+0x...
"WARNING: CPU: X PID: Y at kernel/rcutree.c:2221 rcu_process_callbacks+0x50c/0x570" followed by the ... "WARNING: CPU: X PID: Y at kernel/rcutree.c:2221 rcu_process_callbacks+0x50c/0x570" followed by the crash