From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752589Ab2BRK4J (ORCPT ); Sat, 18 Feb 2012 05:56:09 -0500 Received: from e23smtp05.au.ibm.com ([202.81.31.147]:58163 "EHLO e23smtp05.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751562Ab2BRK4H (ORCPT ); Sat, 18 Feb 2012 05:56:07 -0500 From: "Aneesh Kumar K.V" To: Al Viro , Tyler Hicks Cc: Josh Boyer , Dave Jones , Linux Kernel Subject: Re: hugetlbfs lockdep spew revisited. In-Reply-To: <20120217004922.GN23916@ZenIV.linux.org.uk> References: <20120217000856.GA13112@redhat.com> <20120217001634.GH23550@zod.bos.redhat.com> <20120217003848.GB20071@boyd> <20120217004922.GN23916@ZenIV.linux.org.uk> User-Agent: Notmuch/0.11.1+190~g31a336a (http://notmuchmail.org) Emacs/23.3.1 (x86_64-pc-linux-gnu) Date: Sat, 18 Feb 2012 16:25:38 +0530 Message-ID: <87vcn4cswl.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii x-cbid: 12021800-1396-0000-0000-000000B12BEC Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 17 Feb 2012 00:49:22 +0000, Al Viro wrote: > On Thu, Feb 16, 2012 at 06:38:49PM -0600, Tyler Hicks wrote: > > On 2012-02-16 19:16:34, Josh Boyer wrote: > > > On Thu, Feb 16, 2012 at 07:08:57PM -0500, Dave Jones wrote: > > > > Remember this ? https://lkml.org/lkml/2011/4/15/272 > > > > Josh took a stab at fixing it in e096d0c7e2e4e5893792db865dd065ac73cf1f00, > > > > but it seems to still be there. > > > > > > I think Tyler Hicks actually noticed this a while ago, but his patch has > > > been waiting on comment from Al and Christoph: > > > > > > http://thread.gmane.org/gmane.linux.file-systems/58795/focus=59565 > > > > > > I've been hesitant to comment because I obviously screwed up once > > > already. We could try this patch in Fedora for a while if Al and > > > company don't speak up soon. > > > > I'm pretty confident that my patch that Josh linked to would "fix" the > > lockdep warning below. According to the backtrace, it is barking about a > > directory inode and a regular inode having a circular locking > > dependency, so deadlock is not possible in this case. > > Sigh... That patch is correct, but it has nothing to do with the locking > order violation that really *is* there. The only benefit would be to > get rid of the "deadlock is not possible" nonsense, since you would see > read/write vs. mmap instead of readdir vs. mmap in the traces. Locking > order is the *same* for directories and nondirectories; both can have > pagefaults under ->i_mutex on their respective inodes. And while mmap > cannot happen for directories, it certainly can happen for regular files, > so taking ->i_mutex in ->mmap() is a plain and simple bug. Should never > be done; in particular, hugetlbfs has ->i_mutex held in read() around > pagefaults, which gives you an obvious deadlock with its ->mmap(). > > Folks, this is not a false positive and it has nothing to do with misannotation > for directories. Deadlock is real; I have no idea WTF do we what ->i_mutex > held over that area in hugetlbfs ->mmap(), but doing that is really, really > wrong, whatever the reason. I looked at hugetlbfs recently and noticed this. Another strange thing with hugetlbfs is, it doesn't support write, instead allows to bump the file size via mmap. I don't have a patch for inode->i_mutex issue yet. -aneesh