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SubjectRe: LTTng finds abnormally long APIC interrupt handler : 58.2 ms

Steven Rostedt <> writes:

> [...]
>> It all holds in a small module. Having the ability to connect any marker
>> on any generic probe from the lttng marker interface has been very
>> useful to do all this. Actually, this module has to be built into the
>> kernel because ftrace does not permit breeing the trace_ops data
>> structure. :/
> I did this purposely. The reason is that there is no safe way to release
> the trace_ops, because you never know if something is in the function
> you pointed to. If you remove the module after that, it crashes.
> I've been thinking of exporting it, and make it so that once you
> register something to the trace_ops, I'll up the module count, and never
> let that module unload.

This issue will need some sort of resolution if systemtap is to be
able to hook up to ftrace. Perhaps we could have a second/nested API
that suffers the costs of explicit reference counting, but does permit
dynamic attach and robust detach.

- FChE

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