From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f43.google.com (mail-wm0-f43.google.com [74.125.82.43]) by kanga.kvack.org (Postfix) with ESMTP id 71BB96B0253 for ; Fri, 29 Jan 2016 05:39:45 -0500 (EST) Received: by mail-wm0-f43.google.com with SMTP id l66so61560434wml.0 for ; Fri, 29 Jan 2016 02:39:45 -0800 (PST) Received: from mail-wm0-x22c.google.com (mail-wm0-x22c.google.com. [2a00:1450:400c:c09::22c]) by mx.google.com with ESMTPS id ee2si21312609wjd.88.2016.01.29.02.39.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 29 Jan 2016 02:39:44 -0800 (PST) Received: by mail-wm0-x22c.google.com with SMTP id p63so62107880wmp.1 for ; Fri, 29 Jan 2016 02:39:44 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20160128154746.GI12228@redhat.com> References: <20160127194132.GA896@redhat.com> <20160128154746.GI12228@redhat.com> From: Dmitry Vyukov Date: Fri, 29 Jan 2016 11:39:24 +0100 Message-ID: Subject: Re: mm: BUG in expand_downwards Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Andrea Arcangeli 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 On Thu, Jan 28, 2016 at 4:47 PM, Andrea Arcangeli wrote: > 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? Yes, it seems to fix the issue. I will also run fuzzer with this patch and report if I see it again. > 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); -- 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