Message-ID: <1371878748.6453.82.camel@empanada>
Date:	Sat, 22 Jun 2013 00:25:48 -0500
From:	Tom Zanussi <tom.zanussi@...el.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/11] tracing: fix disabling of soft disable

On Fri, 2013-06-21 at 16:14 -0500, Tom Zanussi wrote:
> On Fri, 2013-06-21 at 16:39 -0400, Steven Rostedt wrote:
> > On Fri, 2013-06-21 at 20:12 +0900, Masami Hiramatsu wrote:
> > > (2013/06/21 3:31), Tom Zanussi wrote:
> > > > The comment on the soft disable 'disable' case of
> > > > __ftrace_event_enable_disable() states that the soft disable bit
> > > > should be cleared in that case, but currently only the soft mode bit
> > > > is actually cleared.
> > > > 
> > > > This essentially leaves the standard non-soft-enable enable/disable
> > > > paths as the only way to clear the soft disable flag, but the soft
> > > > disable bit should also be cleared when removing a trigger with '!'.
> > > 
> > > Indeed, the soft-disabled flag may remain after the event itself
> > > disabled. However that soft-disabled flag will be cleared when
> > > the event is re-enabled. it seems no bad side-effect.
> > > 
> > > Thus I doubt this patch is separately required. I guess this is
> > > required for adding new trigger flag, isn't it? :)
> > 
> > Tom, I'm guessing Masami is correct here. It's needed for the trigger
> > work to work, correct?
> > 
> 
> Well, the trigger should really work without this - this is basically
> just a cleanup I added because it bothered me that I couldn't completely
> revert the enable state back to the original state that existed before I
> added the trigger (by reverting the trigger using '!').  It also just
> seemed obviously correct from looking at the code as well (though I
> agree, it's hard to keep the state machine of that function in your head
> in order to prove it correct, and the straggling soft-disable state
> hasn't bothered anyone until now, so maybe it's not worth it..)
> 

Looking into this a bit more, I think the reason it hasn't bothered
anyone until now is that it's been hidden by the existing
event_enable_read() implementation, which doesn't show any soft disable
state when the event is actually disabled, only when it's enabled.  So
the case where SOFT_DISABLED is still set but the event is actually
disabled gets hidden by the catch-all "0" case.

My new version of event_enable_read() does show the soft disabled state
when the event is actually disabled, which is why I noticed it wasn't
getting turned off, and led to the current patch.

Ironically, the reason I refactored the function in the first place was
to add the '+' flag for triggers - redundant, yes, but useful for
debugging, not quite in the way I planned though.  ;-)  (It might be
that leaving the current function in place and remaining oblivious would
be ok, too, since it doesn't seem to really cause much of a problem in
any case...)

Tom

> In any case, if the SOFT_DISABLED bit is erroneously set but there are
> no triggers, it shouldn't be a problem, since the trigger calls would
> just return immediately, so not having this patch wouldn't break
> anything... 
> 
> Tom
> 
> 
> > Either way, I probably could add it as a clean up patch regardless. I'll
> > just have to test the hell out of it some more, as the accounting for
> > soft-disable vs real disable was a PITA.
> > 
> 
> 
> > -- Steve
> > 
> 


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