From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753525AbZHFBhM (ORCPT ); Wed, 5 Aug 2009 21:37:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752349AbZHFBhL (ORCPT ); Wed, 5 Aug 2009 21:37:11 -0400 Received: from [222.73.24.84] ([222.73.24.84]:49565 "EHLO song.cn.fujitsu.com" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752620AbZHFBhK (ORCPT ); Wed, 5 Aug 2009 21:37:10 -0400 Message-ID: <4A7A336B.4040708@cn.fujitsu.com> Date: Thu, 06 Aug 2009 09:35:39 +0800 From: Li Zefan User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1b3pre) Gecko/20090513 Fedora/3.0-2.3.beta2.fc11 Thunderbird/3.0b2 MIME-Version: 1.0 To: Frederic Weisbecker CC: Ingo Molnar , LKML , Steven Rostedt , Lai Jiangshan , Tom Zanussi , Thomas Gleixner , Peter Zijlstra Subject: Re: [RFC][PATCH 5/5] tracing/filters: Provide support for char * pointers References: <1249111408-8657-1-git-send-email-fweisbec@gmail.com> <1249111408-8657-6-git-send-email-fweisbec@gmail.com> <4A768A87.6090800@cn.fujitsu.com> <20090805230257.GI5025@nowhere> In-Reply-To: <20090805230257.GI5025@nowhere> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Frederic Weisbecker wrote: > On Mon, Aug 03, 2009 at 02:58:15PM +0800, Li Zefan wrote: >> Frederic Weisbecker wrote: >>> Provide support for char * pointers in the filtering framework. >>> Usually, char * entries are dangerous in traces because the string >>> can be released whereas a pointer to it can still wait to be read from >>> the ring buffer. But sometimes we can assume it's safe, like in case >>> of RO data (eg: __file__ or __line__, used in bkl trace event). If >>> these RO data are in a module and so is the call to the trace event, >>> then it's safe, because the ring buffer will be flushed once this >>> module get unloaded. >>> >> The problem is we don't distinguish dangerous char * from >> safe char *... They are both defined as: >> __field(char *, str) >> >> So for those dangerous ones, a string filter still can be applied, >> which will dereference those pointers. > > Yeah, but only reviewing can distinguish them. It depends on the > context. > IMO, a __builtin_constant check would be wrong. I don't remember who > posted recently tracepoints with char * types that were safe although he > didn't use string constants. > IMO it's really bad to rely on review to prevent wrong use of an API.. Other developers won't know this restriction, and not all tracepoint patches go through -tip tree, and not all trace_event source files are in include/trace/events/. How about add __field_type()? So we can define: __field_type(char *, str, FILTER_PTR_STR) the advantage is he who wrote the code really knows this field is safe to be used in filtering as a string. I had some patches that does similar job. I can rewrite and post them.