From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ea0-f177.google.com (mail-ea0-f177.google.com [209.85.215.177]) by kanga.kvack.org (Postfix) with ESMTP id F04226B0031 for ; Fri, 7 Mar 2014 07:18:15 -0500 (EST) Received: by mail-ea0-f177.google.com with SMTP id h10so2271182eak.22 for ; Fri, 07 Mar 2014 04:18:15 -0800 (PST) Received: from jenni1.inet.fi (mta-out.inet.fi. [195.156.147.13]) by mx.google.com with ESMTP id i43si16047807eev.112.2014.03.07.04.18.14 for ; Fri, 07 Mar 2014 04:18:14 -0800 (PST) Date: Fri, 7 Mar 2014 14:18:10 +0200 From: "Kirill A. Shutemov" 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> Sender: owner-linux-mm@kvack.org List-ID: To: Sasha Levin Cc: Bob Liu , "Kirill A. Shutemov" , Andrea Arcangeli , "linux-mm@kvack.org" , Andrew Morton , LKML 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org