Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757054AbbFPU1X (ORCPT ); Tue, 16 Jun 2015 16:27:23 -0400 Received: from mail-wi0-f175.google.com ([209.85.212.175]:37755 "EHLO mail-wi0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754988AbbFPU1U (ORCPT ); Tue, 16 Jun 2015 16:27:20 -0400 Date: Tue, 16 Jun 2015 13:27:05 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Daniel Wagner cc: Linus Torvalds , Prarit Bhargava , Morten Stevens , Dave Chinner , Eric Paris , Eric Sandeen , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS In-Reply-To: <557E6C0C.3050802@monom.org> Message-ID: References: <557E6C0C.3050802@monom.org> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2094 Lines: 48 On Mon, 15 Jun 2015, Daniel Wagner wrote: > On 06/14/2015 06:48 PM, Hugh Dickins wrote: > > It appears that, at some point last year, XFS made directory handling > > changes which bring it into lockdep conflict with shmem_zero_setup(): > > it is surprising that mmap() can clone an inode while holding mmap_sem, > > but that has been so for many years. > > > > Since those few lockdep traces that I've seen all implicated selinux, > > I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which > > v3.13's commit c7277090927a ("security: shmem: implement kernel private > > shmem inodes") introduced to avoid LSM checks on kernel-internal inodes: > > the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail. > > > > This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero > > (and MAP_SHARED|MAP_ANONYMOUS). I thought there were also drivers > > which cloned inode in mmap(), but if so, I cannot locate them now. > > > > Reported-and-tested-by: Prarit Bhargava > > Reported-by: Daniel Wagner > > Reported-and-tested-by: Daniel Wagner Great, thank you Daniel: we look more convincing now :) > > Sorry for the long delay. It took me a while to figure out my original > setup. I could verify that this patch made the lockdep message go away > on 4.0-rc6 and also on 4.1-rc8. Thank you for taking the trouble. > > For the record: SELinux needs to be enabled triggering it. Right, selinux was in all the stacktraces we saw, and I was banking on that security "recursion" being what actually upset lockdep; but couldn't be sure until you tried it out. We didn't make -rc8, and I won't be at all surprised if Linus feels that a year(?)-old lockdep warning is not worth disturbing v4.1 final for, but it should get into v4.2 (thank you, Andrew). Hugh -- 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/