[Bug] Data race in eBPF backend

[kxxt]

eBPF can be preempted after linux v5.11: https://stackoverflow.com/questions/78629652/can-an-ebpf-xdp-thread-be-preempted

This means that many of our per-cpu data structures can have data race.

e.g. Today I got

The application panicked (crashed).
  assertion `left == right` failed
    left: 312
   right: 48
in src/bpf/tracer.rs:356
thread: tokio-runtime-worker

which is a data race between the exec fentry program and a process exit tracepoint eBPF program.