From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753277AbaCGMS1 (ORCPT ); Fri, 7 Mar 2014 07:18:27 -0500 Received: from mta-out.inet.fi ([195.156.147.13]:52377 "EHLO jenni1.inet.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751330AbaCGMSX (ORCPT ); Fri, 7 Mar 2014 07:18:23 -0500 Date: Fri, 7 Mar 2014 14:18:10 +0200 From: "Kirill A. Shutemov" To: Sasha Levin Cc: Bob Liu , "Kirill A. Shutemov" , Andrea Arcangeli , "linux-mm@kvack.org" , Andrew Morton , LKML Subject: Re: mm: kernel BUG at mm/huge_memory.c:2785! Message-ID: <20140307121810.GA6740@node.dhcp.inet.fi> References: <530F3F0A.5040304@oracle.com> <20140227150313.3BA27E0098@blue.fi.intel.com> <53169FC5.4080006@oracle.com> <531921C0.3030904@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <531921C0.3030904@oracle.com> User-Agent: Mutt/1.5.22.1-rc1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 06, 2014 at 08:32:48PM -0500, Sasha Levin wrote: > On 03/04/2014 10:53 PM, Sasha Levin wrote: > >On 03/04/2014 10:16 PM, Bob Liu wrote: > >>On Thu, Feb 27, 2014 at 11:03 PM, Kirill A. Shutemov > >> wrote: > >>>Sasha Levin wrote: > >>>>Hi all, > >>>> > >>>>While fuzzing with trinity inside a KVM tools guest running latest -next kernel I've stumbled on the > >>>>following spew: > >>>> > >>>>[ 1428.146261] kernel BUG at mm/huge_memory.c:2785! > >>> > >>>Hm, interesting. > >>> > >>>It seems we either failed to split huge page on vma split or it > >>>materialized from under us. I don't see how it can happen: > >>> > >>> - it seems we do the right thing with vma_adjust_trans_huge() in > >>> __split_vma(); > >>> - we hold ->mmap_sem all the way from vm_munmap(). At least I don't see > >>> a place where we could drop it; > >>> > >> > >>Enable CONFIG_DEBUG_VM may show some useful information, at least we > >>can confirm weather rwsem_is_locked(&tlb->mm->mmap_sem) before > >>split_huge_page_pmd(). > > > >I have CONFIG_DEBUG_VM enabled and that code you're talking is not triggering, so mmap_sem > >is locked. > > Guess what. I've just hit it. I think this particular traceback is not a real problem: by time of exit_mm() we shouldn't race with anybody for the mm_struct. We probably could drop ->mmap_sem later in mmput() rather then in exit_mm() to fix this false positive. > It's worth keeping in mind that this is the first time I see it. Hm. That's strange exit_mmap() is called without holding ->mmap_sem. -- Kirill A. Shutemov