From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752300Ab2IOAAh (ORCPT ); Fri, 14 Sep 2012 20:00:37 -0400 Received: from mail-pz0-f46.google.com ([209.85.210.46]:35865 "EHLO mail-pz0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751267Ab2IOAAe (ORCPT ); Fri, 14 Sep 2012 20:00:34 -0400 Date: Fri, 14 Sep 2012 17:00:29 -0700 From: Michel Lespinasse To: Sasha Levin Cc: linux-mm@kvack.org, riel@redhat.com, peterz@infradead.org, aarcange@redhat.com, hughd@google.com, daniel.santos@pobox.com, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Dave Jones , Jiri Slaby Subject: Re: [PATCH 6/7] mm: add CONFIG_DEBUG_VM_RB build option Message-ID: <20120915000029.GA29426@google.com> References: <1346750457-12385-1-git-send-email-walken@google.com> <1346750457-12385-7-git-send-email-walken@google.com> <5053AC2F.3070203@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 14, 2012 at 3:46 PM, Michel Lespinasse wrote: > On Fri, Sep 14, 2012 at 3:14 PM, Sasha Levin wrote: >> On 09/04/2012 11:20 AM, Michel Lespinasse wrote: >>> Add a CONFIG_DEBUG_VM_RB build option for the previously existing >>> DEBUG_MM_RB code. Now that Andi Kleen modified it to avoid using >>> recursive algorithms, we can expose it a bit more. >>> >>> Also extend this code to validate_mm() after stack expansion, and to >>> check that the vma's start and last pgoffs have not changed since the >>> nodes were inserted on the anon vma interval tree (as it is important >>> that the nodes be reindexed after each such update). >> >> This patch exposes the following warning: >> >> [ 24.977502] ------------[ cut here ]------------ >> [ 24.979089] WARNING: at mm/interval_tree.c:110 >> anon_vma_interval_tree_verify+0x81/0xa0() >> [ 24.981765] Pid: 5928, comm: trinity-child37 Tainted: G W >> 3.6.0-rc5-next-20120914-sasha-00003-g7deb7fa-dirty #333 >> [ 24.985501] Call Trace: >> [ 24.986345] [] ? anon_vma_interval_tree_verify+0x81/0xa0 >> [ 24.988535] [] warn_slowpath_common+0x86/0xb0 >> [ 24.990636] [] warn_slowpath_null+0x15/0x20 >> [ 24.992658] [] anon_vma_interval_tree_verify+0x81/0xa0 >> [ 24.994980] [] validate_mm+0x58/0x1e0 >> [ 24.996772] [] vma_link+0x94/0xe0 >> [ 24.997719] [] copy_vma+0x279/0x2e0 >> [ 24.998522] [] ? trace_hardirqs_off+0xd/0x10 >> [ 25.000772] [] move_vma+0xa9/0x260 >> [ 25.002499] [] sys_mremap+0x475/0x540 >> [ 25.004364] [] tracesys+0xe1/0xe6 >> [ 25.006108] ---[ end trace 7c901670963aa6e2 ]--- >> >> The code line is >> >> WARN_ON_ONCE(node->cached_vma_last != avc_last_pgoff(node)); > > That's very interesting (and potentially relevant to another bug > that's been reported too). > > I'd like to know, what workload did you use that triggered this ? > (I find it hard to test mremap as I don't know of enough users of it) All right. Hugh managed to reproduce the issue on his suse laptop, and I came up with a fix. The problem was that in mremap, the new vma's vm_{start,end,pgoff} fields need to be updated before calling anon_vma_clone() so that the new vma will be properly indexed. Patch attached. I expect this should also explain Jiri's reported failure involving splitting THP pages during mremap(), even though we did not manage to reproduce that one. ---------------------------------8<------------------------------- From: Michel Lespinasse Date: Fri, 14 Sep 2012 16:43:49 -0700 Subject: [PATCH] mm anon rmap: in mremap, set the new vma's position before anon_vma_clone() anon_vma_clone() expects new_vma->vm_{start,end,pgoff} to be correctly set so that the new vma can be indexed on the anon interval tree. copy_vma() was failing to do that, which broke mremap(). Signed-off-by: Michel Lespinasse --- mm/mmap.c | 8 ++++---- 1 files changed, 4 insertions(+), 4 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index cc8c64077a42..7e672800b5d4 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2446,16 +2446,16 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, new_vma = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL); if (new_vma) { *new_vma = *vma; + new_vma->vm_start = addr; + new_vma->vm_end = addr + len; + new_vma->vm_pgoff = pgoff; pol = mpol_dup(vma_policy(vma)); if (IS_ERR(pol)) goto out_free_vma; + vma_set_policy(new_vma, pol); INIT_LIST_HEAD(&new_vma->anon_vma_chain); if (anon_vma_clone(new_vma, vma)) goto out_free_mempol; - vma_set_policy(new_vma, pol); - new_vma->vm_start = addr; - new_vma->vm_end = addr + len; - new_vma->vm_pgoff = pgoff; if (new_vma->vm_file) { get_file(new_vma->vm_file); -- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies.