From: Dmitriy Monakhov Subject: Re: [PATCH] [RFC] remove ext3 inode from orphan list when link and unlink race Date: Sun, 14 Jan 2007 14:58:08 +0300 Message-ID: <878xg5q0q7.fsf@sw.ru> References: <45A7F384.3050303@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Linux Kernel Mailing List , ext4 development Return-path: Received: from mailhub.sw.ru ([195.214.233.200]:20354 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751248AbXANL54 (ORCPT ); Sun, 14 Jan 2007 06:57:56 -0500 To: Eric Sandeen In-Reply-To: <45A7F384.3050303@redhat.com> (Eric Sandeen's message of "Fri, 12 Jan 2007 14:45:56 -0600") Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org Eric Sandeen writes: > I've been looking at a case where many threads are opening, unlinking, and > hardlinking files on ext3 . How many concurent threads do you use and how long does it takes to trigger this race? I've tried to reproduce this with two threads, but not succeed. fd = create("src") close(fd) unlink("src") link("src", "dst") unlink("dst") Original testcase will be the best answer :). Thanks. > At unmount time I see an oops, because the superblock's > orphan list points to a freed inode. > > I did some tracing of the inodes, and it looks like this: > > ext3_unlink():[/src/linux-2.6.18/fs/ext3/namei.c:2123] adding orphan > i_state:0x7 cpu:1 i_count:2 i_nlink:0 > > ext3_orphan_add():[/src/linux-2.6.18/fs/ext3/namei.c:1890] ext3_orphan_add > i_state:0x7 cpu:1 i_count:2 i_nlink:0 > > iput():[/src/linux-2.6.18/fs/inode.c:1139] iput enter > i_state:0x7 cpu:1 i_count:2 i_nlink:0 > > ext3_link():[/src/linux-2.6.18/fs/ext3/namei.c:2202] ext3_link enter > i_state:0x7 cpu:3 i_count:1 i_nlink:0 > > ext3_inc_count():[/src/linux-2.6.18/fs/ext3/namei.c:1627] done > i_state:0x7 cpu:3 i_count:1 i_nlink:1 > > The unlink gets there first, finds i_count > 0 (in use) but nlink goes to 0, so > it puts it on the orphan inode list. Then link comes along, and bumps the link > back up to 1. So now we are on the orphan inode list, but we are not unlinked. > > Eventually when count goes to 0, and we still have 1 link, again no action is > taken to remove the inode from the orphan list, because it is still linked (i.e. > we don't go through ext3_delete()) > > When this inode is eventually freed, the sb orphan list gets corrupted, because > we have freed it without first removing it from the orphan list. > > I think the simple solution is to remove the inode from the orphan list > when we bump the link back up from 0 to 1. I put that test in there because > there are other potential reasons that we might be on the list (truncates, > direct IO). > > Comments? > > Thanks, > -Eric > > p.s. ext3_inc_count and ext3_dec_count seem misnamed, have an unused > arg, and are very infrequently called. I'll probably submit a patch > to just put the single line of code into the caller, too. > > --- > > Remove inode from the orphan list in ext3_link() if we might have > raced with ext3_unlink(), which potentially put it on the list. > If we're on the list with nlink > 0, we'll never get cleaned up > properly and eventually may corrupt the list. > > Signed-off-by: Eric Sandeen > > Index: linux-2.6.19/fs/ext3/namei.c > =================================================================== > --- linux-2.6.19.orig/fs/ext3/namei.c > +++ linux-2.6.19/fs/ext3/namei.c > @@ -2204,6 +2204,9 @@ retry: > inode->i_ctime = CURRENT_TIME_SEC; > ext3_inc_count(handle, inode); > atomic_inc(&inode->i_count); > + /* did we race w/ unlink? */ > + if (inode->i_nlink == 1) > + ext3_orphan_del(handle, inode); > > err = ext3_add_nondir(handle, dentry, inode); > ext3_journal_stop(handle); > > > - > 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/