From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757858Ab0BQXSO (ORCPT ); Wed, 17 Feb 2010 18:18:14 -0500 Received: from kroah.org ([198.145.64.141]:43002 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757753Ab0BQXSL (ORCPT ); Wed, 17 Feb 2010 18:18:11 -0500 Date: Wed, 17 Feb 2010 14:38:48 -0800 From: Greg KH To: "Eric W. Biederman" Cc: Greg KH , Neil Brown , Tejun Heo , linux-kernel@vger.kernel.org Subject: Re: [PATCH] sysfs: differentiate between locking links and non-links Message-ID: <20100217223848.GA31557@kroah.com> References: <19314.1869.847327.15190@notabene.brown> <20100210230625.GB678@suse.de> <20100211223235.GC30430@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 11, 2010 at 02:47:57PM -0800, Eric W. Biederman wrote: > Greg KH writes: > > > On Thu, Feb 11, 2010 at 01:42:10PM -0800, Eric W. Biederman wrote: > >> 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. > > > > Ugh, why not? > > > > Neil, care to fix this up? > > > #ifdef CONFIG_DEBUG_LOCK_ALLOC > -#define sysfs_dirent_init_lockdep(sd) \ > +#define sysfs_dirent_init_lockdep(sd, type) \ > do { \ > static struct lock_class_key __key; \ > \ > - lockdep_init_map(&sd->dep_map, "s_active", &__key, 0); \ > + lockdep_init_map(&sd->dep_map, "s_active_" type, &__key, 0); \ > } while(0) > #else > #define sysfs_dirent_init_lockdep(sd) do {} while(0) Got it, I've fixed this by hand. thanks, greg k-h