I'm not sure if I get your concerns but let me try to explain what happens
in such cases. please let me know if I misunderstood your point.

1. Install a probe using perf.
  # ./perf probe sdt_tick:loop2



Does this explain your concerns?

No, this was not my concern.
My concern is with two users on the same USDT.
1. First user enables the probe point but doesn't increment the ref_cnt.
via uprobe_register

2. Second user tries to enable the probe point and also increments the
ref_cnt via uprobe_register_refctr.

3. If the second user now removes the probe point via uprobe_unregister.

4. What is the state of the ref_cnt?

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Thanks and Regards
Srikar