From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935233AbcA1Pry (ORCPT ); Thu, 28 Jan 2016 10:47:54 -0500 Received: from mx1.redhat.com ([209.132.183.28]:41352 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934977AbcA1Prt (ORCPT ); Thu, 28 Jan 2016 10:47:49 -0500 Date: Thu, 28 Jan 2016 16:47:46 +0100 From: Andrea Arcangeli To: Dmitry Vyukov Cc: Oleg Nesterov , Konstantin Khlebnikov , Andrew Morton , "Kirill A. Shutemov" , Chen Gang , Michal Hocko , Piotr Kwapulinski , "linux-mm@kvack.org" , LKML , Hugh Dickins , Sasha Levin , syzkaller , Kostya Serebryany , Alexander Potapenko Subject: Re: mm: BUG in expand_downwards Message-ID: <20160128154746.GI12228@redhat.com> References: <20160127194132.GA896@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Wed, Jan 27, 2016 at 10:11:44PM +0100, Dmitry Vyukov wrote: > Sorry, I meant only the second once. The mm bug. > I guess you need at least CONFIG_DEBUG_VM. Run it in a tight parallel > loop with CPU oversubscription (e.g. 32 parallel processes on 2 cores) > for at least an hour. Does this help for the mm bug? >>From 0cc410ae59800444ca929e3dc48e4f1580a95be6 Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli Date: Thu, 28 Jan 2016 16:34:44 +0100 Subject: [PATCH 1/1] mm: validate_mm browse_rb SMP race condition The mmap_sem for reading in validate_mm called from expand_stack is not enough to prevent the argumented rbtree rb_subtree_gap information to change from under us because expand_stack may be running from other threads concurrently which will hold the mmap_sem for reading too. The argumented rbtree is updated with vma_gap_update under the page_table_lock so use it in browse_rb() too to avoid false positives. Reported-by: Dmitry Vyukov Signed-off-by: Andrea Arcangeli --- mm/mmap.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index f384def..8389e03 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -389,8 +389,9 @@ static long vma_compute_subtree_gap(struct vm_area_struct *vma) } #ifdef CONFIG_DEBUG_VM_RB -static int browse_rb(struct rb_root *root) +static int browse_rb(struct mm_struct *mm) { + struct rb_root *root = &mm->mm_rb; int i = 0, j, bug = 0; struct rb_node *nd, *pn = NULL; unsigned long prev = 0, pend = 0; @@ -413,12 +414,14 @@ static int browse_rb(struct rb_root *root) vma->vm_start, vma->vm_end); bug = 1; } + spin_lock(&mm->page_table_lock); if (vma->rb_subtree_gap != vma_compute_subtree_gap(vma)) { pr_emerg("free gap %lx, correct %lx\n", vma->rb_subtree_gap, vma_compute_subtree_gap(vma)); bug = 1; } + spin_unlock(&mm->page_table_lock); i++; pn = nd; prev = vma->vm_start; @@ -474,7 +477,7 @@ static void validate_mm(struct mm_struct *mm) mm->highest_vm_end, highest_address); bug = 1; } - i = browse_rb(&mm->mm_rb); + i = browse_rb(mm); if (i != mm->map_count) { if (i != -1) pr_emerg("map_count %d rb %d\n", mm->map_count, i);