From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753123AbZHEXDD (ORCPT ); Wed, 5 Aug 2009 19:03:03 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752782AbZHEXDD (ORCPT ); Wed, 5 Aug 2009 19:03:03 -0400 Received: from mail-bw0-f222.google.com ([209.85.218.222]:56967 "EHLO mail-bw0-f222.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752400AbZHEXDB (ORCPT ); Wed, 5 Aug 2009 19:03:01 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=H4YTLmxkBhirDM5Raz18QlEWeyJfU9g3E7Np4WUdWY5qOwaMaDv7Rr3zy5/cnmIarX wXSJbkQB7qPpTSjB0QoXrd4As2yi2vJErx4q5kzePTCYySZwD7RyGlzxtrw6bslQGmiY W09kVwmFGhCwe09NQtt3f56095UMXZ2K4CHj4= Date: Thu, 6 Aug 2009 01:02:59 +0200 From: Frederic Weisbecker To: Li Zefan 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 Message-ID: <20090805230257.GI5025@nowhere> References: <1249111408-8657-1-git-send-email-fweisbec@gmail.com> <1249111408-8657-6-git-send-email-fweisbec@gmail.com> <4A768A87.6090800@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A768A87.6090800@cn.fujitsu.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > 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()