From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933144Ab3LIJ5Z (ORCPT ); Mon, 9 Dec 2013 04:57:25 -0500 Received: from mail-ve0-f182.google.com ([209.85.128.182]:35186 "EHLO mail-ve0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932303Ab3LIJ5X (ORCPT ); Mon, 9 Dec 2013 04:57:23 -0500 MIME-Version: 1.0 In-Reply-To: <20131209085526.GB4125@kroah.com> References: <1386502262-1163-1-git-send-email-ethan.kernel@gmail.com> <20131208140100.GA22793@kroah.com> <20131209082527.GA26950@kroah.com> <20131209085526.GB4125@kroah.com> Date: Mon, 9 Dec 2013 17:57:22 +0800 Message-ID: Subject: Re: [PATCH] xen/debugfs: Check debugfs initialization before using it From: Ethan Zhao To: Greg KH Cc: konrad.wilk@oracle.com, raghavendra.kt@linux.vnet.ibm.com, LKML Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 9, 2013 at 4:55 PM, Greg KH wrote: > On Mon, Dec 09, 2013 at 04:44:05PM +0800, Ethan Zhao wrote: >> On Mon, Dec 9, 2013 at 4:25 PM, Greg KH wrote: >> > On Mon, Dec 09, 2013 at 09:43:16AM +0800, Ethan Zhao wrote: >> >> On Sun, Dec 8, 2013 at 10:01 PM, Greg KH wrote: >> >> > On Sun, Dec 08, 2013 at 07:31:02PM +0800, ethan.zhao wrote: >> >> >> Should check debugfs initialization with debugfs_initialized() before using it, >> >> >> Because if it isn't initialized, the return value of fake debugfs_create_dir() etc >> >> >> functions would be ERR_PTR(-ENODEV), checking with NULL will not work. >> >> > >> >> > So? It should "just work" without this check, right? What happens if >> >> > your patch isn't applied and debugfs isn't enabled? >> >> >> >> If debugfs isn't configured, debugfs_initialized() and other >> >> functions are defined as following, >> >> >> >> static inline bool debugfs_initialized(void) >> >> { >> >> return false; >> >> } >> >> >> >> static inline struct dentry *debugfs_create_file(const char *name, umode_t mode, >> >> struct dentry *parent, void *data, >> >> const struct file_operations *fops) >> >> { >> >> return ERR_PTR(-ENODEV); >> >> } >> >> >> >> static inline struct dentry *debugfs_create_dir(const char *name, >> >> struct dentry *parent) >> >> { >> >> return ERR_PTR(-ENODEV); >> >> } >> >> >> >> And the checking code in xen\debugfs.c xen_init_debugfs() will not >> >> work, the return value is not NULL. >> >> d_xen_debug = debugfs_create_dir("xen", NULL); >> >> >> >> if (!d_xen_debug) >> >> pr_warning("Could not create 'xen' debugfs directory\n"); >> > >> > Which is just fine, what is wrong with this? >> >> If we no check with debugfs_initialized(), the above code should be >> if (!d_xen_debug || IS_ERR (d_xen_debug)) >> pr_warning("Could not create 'xen' debugfs directory\n"); > > No, you don't want to print out that message if debugfs is not enabled. > > You really don't want to print anything out, as what can a user do about > this? > Yep, should output a warning about "Debugfs is not configured and enabled" > I still think the original code is correct, have you tried it with > debugfs disabled? If debugfs is not configured, no "Could not create 'xen' debugfs directory" warning. Ok, send V3 to imporve it. > > greg k-h