From: Alex Tomas Subject: Re: [PATCH] [RFC] remove ext3 inode from orphan list when link and unlink race Date: Sat, 13 Jan 2007 00:02:13 +0300 Message-ID: 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 fe02.tochka.ru ([62.5.255.22]:56818 "EHLO umail.ru" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1161004AbXALVCR (ORCPT ); Fri, 12 Jan 2007 16:02:17 -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 interesting .. I thought VFS doesn't allow concurrent operations. if unlink goes first, then link should wait on the parent's i_mutex and then found no source name. thanks, Alex >>>>> Eric Sandeen (ES) writes: ES> ) ES> I've been looking at a case where many threads are opening, unlinking, and ES> hardlinking files on ext3 . At unmount time I see an oops, because the superblock's ES> orphan list points to a freed inode. ES> I did some tracing of the inodes, and it looks like this: ES> ext3_unlink():[/src/linux-2.6.18/fs/ext3/namei.c:2123] adding orphan ES> i_state:0x7 cpu:1 i_count:2 i_nlink:0 ES> ext3_orphan_add():[/src/linux-2.6.18/fs/ext3/namei.c:1890] ext3_orphan_add ES> i_state:0x7 cpu:1 i_count:2 i_nlink:0 ES> iput():[/src/linux-2.6.18/fs/inode.c:1139] iput enter ES> i_state:0x7 cpu:1 i_count:2 i_nlink:0 ES> ext3_link():[/src/linux-2.6.18/fs/ext3/namei.c:2202] ext3_link enter ES> i_state:0x7 cpu:3 i_count:1 i_nlink:0 ES> ext3_inc_count():[/src/linux-2.6.18/fs/ext3/namei.c:1627] done ES> i_state:0x7 cpu:3 i_count:1 i_nlink:1 ES> The unlink gets there first, finds i_count > 0 (in use) but nlink goes to 0, so ES> it puts it on the orphan inode list. Then link comes along, and bumps the link ES> back up to 1. So now we are on the orphan inode list, but we are not unlinked. ES> Eventually when count goes to 0, and we still have 1 link, again no action is ES> taken to remove the inode from the orphan list, because it is still linked (i.e. ES> we don't go through ext3_delete()) ES> When this inode is eventually freed, the sb orphan list gets corrupted, because ES> we have freed it without first removing it from the orphan list. ES> I think the simple solution is to remove the inode from the orphan list ES> when we bump the link back up from 0 to 1. I put that test in there because ES> there are other potential reasons that we might be on the list (truncates, ES> direct IO). ES> Comments? ES> Thanks, ES> -Eric ES> p.s. ext3_inc_count and ext3_dec_count seem misnamed, have an unused ES> arg, and are very infrequently called. I'll probably submit a patch ES> to just put the single line of code into the caller, too. ES> --- ES> Remove inode from the orphan list in ext3_link() if we might have ES> raced with ext3_unlink(), which potentially put it on the list. ES> If we're on the list with nlink > 0, we'll never get cleaned up ES> properly and eventually may corrupt the list. ES> Signed-off-by: Eric Sandeen ES> Index: linux-2.6.19/fs/ext3/namei.c ES> =================================================================== ES> --- linux-2.6.19.orig/fs/ext3/namei.c ES> +++ linux-2.6.19/fs/ext3/namei.c ES> @@ -2204,6 +2204,9 @@ retry: inode-> i_ctime = CURRENT_TIME_SEC; ES> ext3_inc_count(handle, inode); ES> atomic_inc(&inode->i_count); ES> + /* did we race w/ unlink? */ ES> + if (inode->i_nlink == 1) ES> + ext3_orphan_del(handle, inode); ES> err = ext3_add_nondir(handle, dentry, inode); ES> ext3_journal_stop(handle); ES> - ES> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in ES> the body of a message to majordomo@vger.kernel.org ES> More majordomo info at http://vger.kernel.org/majordomo-info.html