linux-kernel - Re: [Bug #11996] Tracing framework regression in 2.6.28-rc3

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Message-ID: <alpine.DEB.1.10.0811161741050.2919@gandalf.stny.rr.com>
Date:	Sun, 16 Nov 2008 17:44:39 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Pekka Paalanen <pq@....fi>
cc:	Ingo Molnar <mingo@...e.hu>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Bug #11996] Tracing framework regression in 2.6.28-rc3


On Mon, 17 Nov 2008, Pekka Paalanen wrote:

> On Sun, 16 Nov 2008 17:35:18 +0100 (CET)
> "Rafael J. Wysocki" <rjw@...k.pl> wrote:
> 
> > This message has been generated automatically as a part of a report
> > of recent regressions.
> > 
> > The following bug entry is on the current list of known regressions
> > from 2.6.27.  Please verify if it still should be listed and let me know
> > (either way).
> > 
> > 
> > Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=11996
> > Subject		: Tracing framework regression in 2.6.28-rc3
> > Submitter	: Pekka Paalanen <pq@....fi>
> > Date		: 2008-11-09 10:13 (8 days old)
> > References	: http://marc.info/?l=linux-kernel&m=122624392229317&w=4
> > Handled-By	: Steven Rostedt <rostedt@...dmis.org>
> 
> Steve, Ingo, did you get into an agreement on the patch?
> What should I test?
> 
> I see -rc5 is out, but I didn't spot the fix in the changelog.
> 
> (The ring buffer NULL dereference on resize / unallocated max tracer.)

Ingo's solution was to have the ring_buffer_resize return success on NULL 
buffer being passed in. Although I agree that it should not crash when 
passed a NULL pointer, I feel that a NULL pointer should return a -1 
(failure). The caller of the code (one place in kernel/trace/trace.c) 
could simply check if the buffer was allocated, and if not, simply ignore 
it.

I agree with Ingo that my original solution was too much churn. But the 
simple if statement and "indent" change is what I feel to be the solution, 
not letting the ring buffer return success on NULL pointer.

-- Steve

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