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

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Message-ID: <49E06C05.2060502@cn.fujitsu.com>
Date:	Sat, 11 Apr 2009 18:08:05 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Tom Zanussi <tzanussi@...il.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

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
> 

Hm, I didn't notice it, since I just started looking into tracing/filters
2 days ago.

>>>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.
>  

I'll keep an eye on this issue.
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