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SubjectRe: [PATCH] ftrace: fix current_tracer error return

On Wed, 29 Oct 2008, Fr?d?ric Weisbecker wrote:
> >
> > My test scripts automatically set or unset /proc/sys/kernel/ftrace_enabled
> >
> > I believe I wanted that to be default off when dynamic ftrace was not
> > active. Currently, it really shouldn't matter, because there's a check to
> > make sure that ftrace has a registered function before calling it.
> >
> > That was just my preference. But if you find it less confusing, then
> > having ftrace_enabled as default on even when dynamic ftrace is not
> > enabled, is fine with me.
> >
> > -- Steve
> >
> >
>
> Thanks. I guess this bug was there for several days. But since I

But this was not a bug :-/

I believe I purposely set it that way. The bug was that you did not know
that you could enable it with /proc/sys/kernel/ftrace_enabled ;-)


> always used dynamic ftrace, I've not
> seen it until yesterday. (BTW I didn't tested with dynamic since this
> patch). I had one other bug that made the set of
> function tracer blocking during the write on current_trace with
> dynamic ftrace. I will have a look on it.

Hmm, that could be a bug, but I do not know the details.

>
> Actually one thing that makes me a bit confused is the use of these
> two vars: ftrace_enabled and ftrace_disabled.
> They are not used for the same purpose but their name suggest the same
> role.... :-)

Well, the code documents it pretty well:

/* ftrace_enabled is a method to turn ftrace on or off */
int ftrace_enabled __read_mostly;
static int last_ftrace_enabled;

/*
* ftrace_disabled is set when an anomaly is discovered.
* ftrace_disabled is much stronger than ftrace_enabled.
*/
static int ftrace_disabled __read_mostly;

-- Steve



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