From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755159Ab2CGKmp (ORCPT ); Wed, 7 Mar 2012 05:42:45 -0500 Received: from cantor2.suse.de ([195.135.220.15]:54119 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753372Ab2CGKmo (ORCPT ); Wed, 7 Mar 2012 05:42:44 -0500 Date: Wed, 7 Mar 2012 11:42:40 +0100 From: Jan Kara To: Fengguang Wu Cc: Jan Kara , Dave Jones , Linux Kernel , Fedora Kernel Team , viro@ZenIV.linux.org.uk, Christoph Hellwig Subject: Re: inode->i_wb_list corruption. Message-ID: <20120307104240.GB18658@quack.suse.cz> References: <20120306185137.GA15881@redhat.com> <20120306210307.GC8781@quack.suse.cz> <20120307072608.GA24087@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120307072608.GA24087@localhost> 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 Tue 06-03-12 23:26:08, Wu Fengguang wrote: > On Tue, Mar 06, 2012 at 10:03:07PM +0100, Jan Kara wrote: > > On Tue 06-03-12 13:51:37, Dave Jones wrote: > > > We've had three separate reports against 3.2.x recently where the linked list debugging > > > is getting tripped up by the prev->next pointer being null instead of pointing > > > to the current list entry while walking the i_wb_list > > > > > > Call traces are slightly different each time, but all end up walking i_wb_list > > > in dput -> d_kill -> i_put -> evict -> inode_wb_list_del > > > > > > What protects that list ? It looks to be just bdi->wb.list_lock ? > > > > > > > > > full reports at: > > > https://bugzilla.redhat.com/show_bug.cgi?id=784741 > > > https://bugzilla.redhat.com/show_bug.cgi?id=799229 > > > https://bugzilla.redhat.com/show_bug.cgi?id=799692 > > Hum, interesting! I'd guess this might be caused by f758eeab - adding > > Fengguang and Christoph to CC. But I'm really failing to see how this could > > happen but interesting thing is that in two of the three cases the files > > are on virtual filesystems (once cgroup, once sysfs). These both use > > noop_backing_dev_info. > > sysfs/cgroup forgot to init inode->i_wb_list? Umm, it's not *that* simple I'd say. E.g. sysfs doesn't provide alloc_inode() method so we use inode_cachep for allocations. And that cache is configured to use inode_init_once(). Also note that the error message is: list_del corruption. prev->next should be ffff8801c2f41b18, but was (null) Which means that our inode had correct i_wb_list.prev but the previous inode had NULL in i_wb_list.next. But that means that both inodes were linked into the list at some point. So it does not seem like an initialization issue to me... Honza > --- linux.orig/fs/inode.c 2012-02-22 19:20:48.374799955 -0800 > +++ linux/fs/inode.c 2012-03-06 23:11:29.133899478 -0800 > @@ -193,6 +193,7 @@ int inode_init_always(struct super_block > inode->i_private = NULL; > inode->i_mapping = mapping; > INIT_LIST_HEAD(&inode->i_dentry); /* buggered by rcu freeing */ > + INIT_LIST_HEAD(&inode->i_wb_list); > #ifdef CONFIG_FS_POSIX_ACL > inode->i_acl = inode->i_default_acl = ACL_NOT_CACHED; > #endif