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

["dsmith at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

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

--- Comment #7 from David Smith <dsmith at redhat dot com> ---
(In reply to Peter Allin from comment #6)
> (In reply to David Smith from comment #5)
> > On my F20 vm (3.16.3-200.fc20.x86_64), your test program and script worked
> > fine (even at WAIT_US 1). What kernel are you running?
> 
> That sounds promising :-) I am running a kernel supplied by the Ubuntu
> project, they call it "3.13.0-24-generic #47-Ubuntu". I am working remotely
> today, and won't risk loosing access to the server by messing a kernel
> upgrade up (got to get that remote power switch configured..), but I'll
> defintely try upgrading it on monday.
> 
> > When you finally stopped systemtap, did it report any skipped probes?
> 
> No I haven't seen any such reports. I stop it either by ctrl-c or by running
> it under the "timeout" command. Could these ways of stopping it inhibit
> messages about skipped probes?

The skipped probes message would have come out at the end after either using
ctrl-c or using the timeout command.

> > Depending on what you get with test2.stp, can I ask you to try with HEAD
> > systemtap and see what you get?
> 
> The behavior is consistent with my version of the script. If I run the
> testprogram with the -c option of stap, I gets equals counts. When I run the
> test program in the background only "func1" is counted. (I don't know if
> this could give any hints, if I switch the order of the probes in the .stp
> file, it is "func2" that works).
> 
> Given this result, whould it make sense to try out the HEAD systemtap?

It might if you have the time. It will provide another data point to whether
this is a kernel issue or a systemtap issue.

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