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

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Date:	Sat, 11 Apr 2009 04:30:48 -0500
From:	Tom Zanussi <tzanussi@...il.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH 0/7] tracing: bug fixes for tracing/filters

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

> 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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