[Bug uprobes/17623] Sometimes probes fail to fire events when running against a multi-threaded application

["peter at peca dot dk" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=17623

--- Comment #3 from Peter Allin <peter at peca dot dk> ---
(In reply to Frank Ch. Eigler from comment #2)
> Peter, have you by any chance tried out "perf probe" against your
> original binary, to see if this is may be a kernel-side rather
> than stap-side problem?

I have just tried it, and am somewhat confused by the results. Here is what I
did:

- perf probe -x testprog func1
- perf probe -x testprog func2
- Start testprog in another terminal
- perf stat -e probe_testprog:func1 -e probe_testprog:func2 -a sleep 1

I ran the last command in a loop for 1000 times. It always shows counts for
both probe points, but the counts are not equal. So it seems that SystemTap
will either work perfectly or loose all events from one of the probes, while
perf is always missing some events but not all.

Do you think this is caused by two separate problems, or are both pointing
towards a kernel problem?

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