From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757184Ab0BKVmU (ORCPT ); Thu, 11 Feb 2010 16:42:20 -0500 Received: from out02.mta.xmission.com ([166.70.13.232]:47177 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757145Ab0BKVmP (ORCPT ); Thu, 11 Feb 2010 16:42:15 -0500 To: Greg KH Cc: Neil Brown , Tejun Heo , linux-kernel@vger.kernel.org Subject: Re: [PATCH] sysfs: differentiate between locking links and non-links References: <19314.1869.847327.15190@notabene.brown> <20100210230625.GB678@suse.de> From: ebiederm@xmission.com (Eric W. Biederman) Date: Thu, 11 Feb 2010 13:42:10 -0800 In-Reply-To: <20100210230625.GB678@suse.de> (Greg KH's message of "Wed\, 10 Feb 2010 15\:06\:25 -0800") Message-ID: User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-XM-SPF: eid=;;;mid=;;;hst=in01.mta.xmission.com;;;ip=76.21.114.89;;;frm=ebiederm@xmission.com;;;spf=neutral X-SA-Exim-Connect-IP: 76.21.114.89 X-SA-Exim-Mail-From: ebiederm@xmission.com X-SA-Exim-Scanned: No (on in01.mta.xmission.com); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Greg KH writes: > On Wed, Feb 10, 2010 at 12:09:33PM +1100, Neil Brown wrote: >> >> Hi, >> I've just spent a while sorting out some lockdep complaints triggered >> by the recent addition of the "s_active" lockdep annotation in sysfs >> (commit 846f99749ab68bbc7f75c74fec305de675b1a1bf) >> >> Some of them are genuine and I have submitted a fix for those. >> Some are, I think, debatable and I get to that is a minute. I've >> submitted a fix for them anyway. >> But some are to my mind clearly bogus and I'm hoping that can be >> fixed by the change below (or similar). >> The 'bogus' ones are triggered by writing to a sysfs attribute file >> for which the handler tries to delete a symlink from sysfs. >> This appears to be a recursion on s_active as s_active is held while >> the handler runs and is again needed to effect the delete. However >> as the thing being deleted is a symlink, it is very clearly a >> different object to the thing triggering the delete, so there is no >> real loop. >> >> The following patch splits the lockdep context in two - one for >> symlink and one for everything else. This removes the apparent loop. >> (An example report can be seen in >> http://bugzilla.kernel.org/show_bug.cgi?id=15142). >> >> The "debatable" dependency loops happen when writing to one attribute >> causes a different attribute to be deleted. In my (md) case this can >> actually cause a deadlock as both the attributes take the same lock >> while the handler is running. This is because deleting the attribute >> will block until the all accesses of that attribute have completed (I >> think). >> However it should be possible to delete a name from sysfs while there >> are still accesses pending (it works for normal files!!). So if >> sysfs could be changed to simply unlink the file and leave deletion to >> happen when the refcount become zero it would certainly make my life >> a lot easier, and allow the removal of some ugly code from md.c. >> I don't know sysfs well enough to suggest a patch though. >> >> Thanks, >> NeilBrown >> >> >> >> commit 2e502cfe444b68f6ef6b8b2abe83b6112564095b >> Author: NeilBrown >> Date: Wed Feb 10 09:43:45 2010 +1100 >> >> sysfs: differentiate between locking links and non-links for sysfs >> >> symlinks and non-symlink is sysfs are very different. >> A symlink can never be locked (active) while an attribute >> modification routine is running. So removing symlink from an >> attribute 'store' routine should be permitted without any lockdep >> warnings. >> >> So split the lockdep context for 's_active' in two, one for symlinks >> and other for everything else. >> >> Signed-off-by: NeilBrown > > Nice patch, I'll queue it up for .34. Note the patch does not compile with lockdep disabled. Eric