linux-kernel - Re: [PATCH 0/7] tracing: bug fixes for tracing/filters

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Message-ID: <20090411144823.GB5977@nowhere>
Date:	Sat, 11 Apr 2009 16:48:33 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Tom Zanussi <tzanussi@...il.com>
Cc:	Li Zefan <lizf@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH 0/7] tracing: bug fixes for tracing/filters

On Sat, Apr 11, 2009 at 04:30:48AM -0500, Tom Zanussi wrote:
> Hi,
> 
> On Sat, 2009-04-11 at 15:52 +0800, Li Zefan wrote:
> > This patchset fixes some bugs in tracing/filters. Most of the change
> > goes to the last patch, and others are small ones.
> > 
> 
> At first glance, they look good and fix real problems - thanks for
> fixing them.  Re patch 7, there's been some discussion about using rcu
> for this.  See:
> 
> http://lkml.org/lkml/2009/4/5/46
> 
> >From that discussion, it seems some non-trivial changes to rcu would be
> needed for this.  I'm playing around with a different idea now to
> hopefully avoid the need for that, or the other approach mentioned, of
> temporarily stopping tracing while removing/changing the filters.
> 
> Basically my thought is to avoid the problem by not allocating or
> destroying the preds when removing filters but instead switch out the
> pred->fns with a nop version while keeping the fields intact for awhile.
> I think that will work for removing filters, but I still need to think
> about how it would (or would not) work for replacing them.
>  
> Tom



It would be sort of reinventing rcu :-)
Well, Paul proposed something recently, hmm I should double check
this discussion.

Anyway, the fixes from Li (other than 4 and 7 for which we have comments)
look very good!

Frederic.



> 
> > Maybe 3rd to 6th patches can be regarded as small enhancements instead
> > of bug fixes? But they are behavioural changes.
> > 
> > 
> > [PATCH 1/7] tracing/filters: NUL-terminate user input filter
> > [PATCH 2/7] tracing/filters: fix NULL pointer dereference
> > [PATCH 3/7] tracing/filters: allow user input integer to be oct or hex
> > [PATCH 4/7] tracing/filters: allow user to specify a filter val to be string
> > [PATCH 5/7] tracing/filters: disallow newline as delimeter
> > [PATCH 6/7] tracing/filters: return proper error code when writing filter file
> > [PATCH 7/7] tracing/filters: make filter preds RCU safe
> > 
> >  kernel/trace/trace.h                |    6 +-
> >  kernel/trace/trace_events.c         |   16 +++--
> >  kernel/trace/trace_events_filter.c  |  131 ++++++++++++++++++++++++++---------
> >  kernel/trace/trace_events_stage_3.h |   10 +++-
> >  4 files changed, 121 insertions(+), 42 deletions(-)
> > ---
> 

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