From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752523AbZHCG7t (ORCPT ); Mon, 3 Aug 2009 02:59:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752220AbZHCG7s (ORCPT ); Mon, 3 Aug 2009 02:59:48 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:63614 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752211AbZHCG7s (ORCPT ); Mon, 3 Aug 2009 02:59:48 -0400 Message-ID: <4A768A87.6090800@cn.fujitsu.com> Date: Mon, 03 Aug 2009 14:58:15 +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> In-Reply-To: <1249111408-8657-6-git-send-email-fweisbec@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > Now the bkl events becomes more useful. Say that you want to trace > only the bkl use in reiserfs: > > cd /debug/tracing/events/bkl/lock_kernel > echo "file == fs/reiserfs*" > filter_regex > cat /debug/tracing/trace > > syslogd-3658 [001] 1874.661878: lock_kernel: depth: 1, fs/reiserfs/super.c:563 reiserfs_dirty_inode() > syslogd-3658 [001] 1874.662266: lock_kernel: depth: 0, fs/reiserfs/inode.c:2695 reiserfs_write_end() > syslogd-3658 [001] 1874.662268: lock_kernel: depth: 1, fs/reiserfs/super.c:563 reiserfs_dirty_inode() > syslogd-3658 [001] 1874.662291: lock_kernel: depth: 0, fs/reiserfs/inode.c:2695 reiserfs_write_end()