From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754620Ab3AYOi5 (ORCPT ); Fri, 25 Jan 2013 09:38:57 -0500 Received: from ironport2-out.teksavvy.com ([206.248.154.182]:39715 "EHLO ironport2-out.teksavvy.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751896Ab3AYOiy (ORCPT ); Fri, 25 Jan 2013 09:38:54 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AtkGAG6Zu0/O+Ip3/2dsb2JhbABEgXuyFoEIghUBAQUnExsBIxALGAklDwUlJBOIDroJj2JiA4hCjFiOGYFYgwc X-IronPort-AV: E=Sophos;i="4.75,637,1330923600"; d="scan'208";a="213654485" Date: Fri, 25 Jan 2013 09:38:51 -0500 From: Mathieu Desnoyers To: Steven Rostedt Cc: Al Viro , linux-kernel@vger.kernel.org, Linus Torvalds Subject: Re: [tracepoint] cargo-culting considered harmful... Message-ID: <20130125143850.GA20597@Krystal> References: <20130123225523.GY4939@ZenIV.linux.org.uk> <20130123230235.GC5434@home.goodmis.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <20130123230235.GC5434@home.goodmis.org> X-Editor: vi User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Steven Rostedt (rostedt@goodmis.org) wrote: > On Wed, Jan 23, 2013 at 10:55:24PM +0000, Al Viro wrote: > > In samples/tracepoints/tracepoint-probe-sample.c: > > /* > > * Here the caller only guarantees locking for struct file and struct inode. > > * Locking must therefore be done in the probe to use the dentry. > > */ > > static void probe_subsys_event(void *ignore, > > struct inode *inode, struct file *file) > > { > > path_get(&file->f_path); > > dget(file->f_path.dentry); > > printk(KERN_INFO "Event is encountered with filename %s\n", > > file->f_path.dentry->d_name.name); > > dput(file->f_path.dentry); > > path_put(&file->f_path); > > } > > > > note that > > * file->f_path is already pinned down by open(), path_get() does not > > provide anything extra. > > * file->f_path.dentry is already pinned by open() *and* path_get() > > just above that dget(). > > * ->d_name.name *IS* *NOT* *PROTECTED* by pinning dentry down, > > whether it's done once or thrice. > > > > I do realize that it's just an example, but perhaps we should rename that > > file to match the contents? The only question is whether it should be > > git mv samples/tracepoints/{tracepoint-probe-sample,cargo-cult}.c > > or git mv samples cargo-cult... > > I wonder if we should just remove the samples/tracepoints/ all together. > The tracepoint code is now only used internally by the trace_event code, > and there should not be any users of tracepoints directly. Yep, I'd be OK with removing this example, since now all users are expected to user TRACE_EVENT(), which is built on top of tracepoints. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com