linux-kernel - Re: [PATCH 1/1] ftrace: do not update max buffer with no users

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Message-ID: <20081113083935.GC25479@elte.hu>
Date:	Thu, 13 Nov 2008 09:39:35 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Pekka Paalanen <pq@....fi>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 1/1] ftrace: do not update max buffer with no users


* Steven Rostedt <rostedt@...dmis.org> wrote:

> 
> 
> On Wed, 12 Nov 2008, Andrew Morton wrote:
> > 
> > 
> > This sort of thing:
> > 
> > +#ifdef CONFIG_TRACER_MAX_TRACE
> >  	if (current_trace && current_trace->print_max)
> >  		iter->tr = &max_tr;
> >  	else
> > +#endif
> >  		iter->tr = inode->i_private;
> > 
> > is particularly regrettable.
> 
> Another answer is to not allocate it and check for NULL before using it. 
> But this would mean that I would have to find all the places that touch it 
> (the same as the ifdefs) and make sure they are safe.
> 
> The reason I picked the ifdefs was to guarantee that there were no users 
> if it was not being used.

Since this is a regression, the best answer is usually the smallest 
possible patch. Which by all likelyhood would be the removal of 
CONFIG_TRACER_MAX_TRACE uses:

 ./kernel/trace/trace.c:#ifdef CONFIG_TRACER_MAX_TRACE
 ./trace.c:#ifdef CONFIG_TRACER_MAX_TRACE
 ./trace.c:#ifdef CONFIG_TRACER_MAX_TRACE

Note, please dont touch the Kconfig - that's just unnecessary churn 
that does nothing to resolve the regression. We'll have an unused 
symbol (and we'll fix it for real in the devel branches) but that's 
not an issue for .28.

Ok?

	Ingo
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