From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753399AbbDGIgX (ORCPT ); Tue, 7 Apr 2015 04:36:23 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:48066 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753131AbbDGIgU (ORCPT ); Tue, 7 Apr 2015 04:36:20 -0400 Date: Tue, 7 Apr 2015 10:36:16 +0200 From: Greg KH To: Tom Van Braeckel Cc: rusty@rustcorp.com.au, lguest@lists.ozlabs.org, linux-kernel@vger.kernel.org, fengguang.wu@intel.com, lkp@01.org Subject: Re: [PATCH] lguest: explicitly setup /dev/lguest private_data Message-ID: <20150407083616.GA14409@kroah.com> References: <20150406121022.GA3867@wfg-t540p.sh.intel.com> <1428394698-16938-1-git-send-email-tomvanbraeckel@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1428394698-16938-1-git-send-email-tomvanbraeckel@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 07, 2015 at 10:18:18AM +0200, Tom Van Braeckel wrote: > The private_data member of the /dev/lguest device file is used to hold > the current struct lguest and needs to be set to NULL to signify that > no initialization has taken place. > > We explicitly set it to NULL to be independent of whatever value the > misc subsystem initializes it to. > > Signed-off-by: Tom Van Braeckel > --- > Backstory: > ========== > The misc subsystem used to initialize a file's private_data to point to > the misc device when a driver had registered a custom open file > operation and initialized it to NULL when a custom open file operation > had *not* been provided. > > This subtle quirk was confusing, to the point where kernel code > registered *empty* file open operations to have private_data point to > the misc device structure. > > And it lead to bugs, where the addition or removal of a custom open > file operation surprisingly changed the initial contents of a file's > private_data structure. > > The misc subsystem is currently underdoing changes to *always* set > private_data to point to the misc device instead of only doing this > when a custom open file operation has been registered. > > Intel's 0day kernel testing robot discovered that the lguest driver > depended on it implicitly being initialized to NULL, as Fengguang Wu > reported. Thanks a lot for all the hard work! > > drivers/lguest/lguest_user.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) I can take this through my char-misc tree, where this misc core change was, if the lguest maintainer (i.e. Rusty) acks it. Tom, thanks for tracking this down. greg k-h