[PATCH 1/1] x86: fix text_poke

[Masami Hiramatsu]

Jeremy Fitzhardinge wrote:
> Mathieu Desnoyers wrote:
>> This idea has been considered a few years ago at OLS in the tracing BOF
>> if I remember well.  The results were this : First, there is no way to
>> guarantee that no code path, nor any return address from any function,
>> interrupt, sleeping thread, will return to the "old" version of the
>> function. Nor is it possible to determine when a quiescent state is
>> reached. Therefore, we couldn't see how we can do the teardown.
>>   
> 
> Does that matter?  The new function is semantically identical to the old 
> one, and the old code will remain in place.  If there's still users in 
> the old function it may take a while for them to get flushed out (and 
> won't be traced in the meantime), but you have to expect some missed 
> events if you're shoving any kind of dynamic marker into the code.  The 
> main problem is if there's something still depending on the first 5 
> bytes of the function (most likely if there's a loop head somewhere near 
> the top of the function).

I think we have to ensure no threads sleeping or being interrupted on
the function when removing new function. How would you check it?

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com