[Bug 217174] dtrace does not cleanup probes

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=217174

            Bug ID: 217174
           Summary: dtrace does not cleanup probes
           Product: Base System
           Version: 10.3-STABLE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: daniel.genis at gmx.de

Created attachment 180077
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=180077&action=edit
DTrace script causing problem

Running and stopping a DTrace script, may leave a "ftcleanup" process behind in
"DL" state, ps afux output:

root     820   0.0  0.0      0    16  -  DL    1:43PM  0:00.01 [ftcleanup]

Perl scripts (for some reason) notice this and show the following warning
afterwards:

WARNING: number of probes fixed does not match the number of defined probes (16
!= 18, respectively)
WARNING: some probes might not fire or your program might crash


This is reproducible on 10.3-STABLE and 10.3-RELEASE, and may take two or three
attempts if it doesn't occur on the first attempt.


How to reproduce:

1. Execute attached dtracte script.
2. Stop executed dtrace script.
3. Check ps afux for kernel ftcleanup process
4. Repeat above until bug is triggered (2-3 times total should be enough)


Any perl script subsequently will print the following warning on stderr, like
this script for example:

```
#!/usr/local/bin/perl
print "Test";
```

WARNING: number of probes fixed does not match the number of defined probes (16
!= 18, respectively)
WARNING: some probes might not fire or your program might crash


I can also reproduce this with other dtrace scripts, like this one:
https://gist.github.com/genisd/72db1d98b64d9d7127570fff7d4b89f6


I don't know how big the implications are. One of our automation scripts dies
due to the stderr output (it checks on that).

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