[Bug bpf/26109] New: bug when begin probe exits quickly

[me at serhei dot io]

https://sourceware.org/bugzilla/show_bug.cgi?id=26109

            Bug ID: 26109
           Summary: bug when begin probe exits quickly
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: bpf
          Assignee: systemtap at sourceware dot org
          Reporter: me at serhei dot io
  Target Milestone: ---

if a bpf begin probe sets exit status, the main thread will skip the pause()
call and immediately deallocate global data structures. Then the
perf_event_loop thread will run on the corrupted data and occasionally fail.
Example result is an assertion failure due count_active_cpus() running on
corrupted data.

Could change the main thread to join() instead of detach(), but then all
threads must be modified to listen for exit status including exit status from
begin thread.

I think if the begin probe was running, it wasn't correct to start the
perf_event_loop (or PERF_EVENT_IOC_ENABLE, or any of the procfs threads) in the
first place, as those things logically happen after the begin probe has already
exited. Simply clean up and exit.

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