Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758153Ab3DAVok (ORCPT ); Mon, 1 Apr 2013 17:44:40 -0400 Received: from mail-pa0-f47.google.com ([209.85.220.47]:43310 "EHLO mail-pa0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754579Ab3DAVoi (ORCPT ); Mon, 1 Apr 2013 17:44:38 -0400 Date: Mon, 1 Apr 2013 14:44:36 -0700 From: Greg Kroah-Hartman To: Al Viro Cc: Linus Torvalds , Dave Jones , Linux Kernel Subject: Re: Yet another pipe related oops. Message-ID: <20130401214436.GA5786@kroah.com> References: <20130312194353.GI21522@ZenIV.linux.org.uk> <20130327135127.GB1738@redhat.com> <20130327152030.GY21522@ZenIV.linux.org.uk> <20130327174506.GZ21522@ZenIV.linux.org.uk> <20130401203445.GA20862@ZenIV.linux.org.uk> <20130401210029.GA3245@kroah.com> <20130401212142.GD21522@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130401212142.GD21522@ZenIV.linux.org.uk> 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 Content-Length: 1603 Lines: 39 On Mon, Apr 01, 2013 at 10:21:42PM +0100, Al Viro wrote: > On Mon, Apr 01, 2013 at 02:00:29PM -0700, Greg Kroah-Hartman wrote: > > > > IOW, how do we deal with a race between attempt to open a debugfs file and > > > its removal on driver unload? Greg? > > > > Hm, I thought the i_fop->owner thing would be the needed protection, but > > It will be, if you manage to fetch it... I agree. > > I guess you are right, it will not. I guess we need to do what > > character devices do and have an "intermediate" fops in order to protect > > this. Would that work? > > You mean, with reassigning ->f_op in ->open()? That'll work, as long as > we have exclusion between removal and fetching the sucker in primary > ->open()... Where would you prefer to stash fops? Ick, that's not going to work as the current api just uses a fops and debugfs doesn't keep anything else hanging around that referes to something "before" that, like 'struct cdev' does. And, it's even worse, look at the use of DEFINE_SIMPLE_ATTRIBUTE(), those take a pointer from a random module to read/write from, and use the fops for the debugfs module. Hopefully no other user of that macro has the same problem, and at first glance, I think that's true, but I might be wrong... Am I allowed to "punt" and say, "removing a module that uses debugfs is not recommended?" :) greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/