From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751625Ab2LAG4u (ORCPT ); Sat, 1 Dec 2012 01:56:50 -0500 Received: from mail-da0-f46.google.com ([209.85.210.46]:44256 "EHLO mail-da0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751203Ab2LAG4t (ORCPT ); Sat, 1 Dec 2012 01:56:49 -0500 From: Michel Lespinasse To: linux-mm@kvack.org, Rik van Riel , Hugh Dickins , Andrew Morton Cc: linux-kernel@vger.kernel.org Subject: [PATCH] mm: protect against concurrent vma expansion Date: Fri, 30 Nov 2012 22:56:27 -0800 Message-Id: <1354344987-28203-1-git-send-email-walken@google.com> X-Mailer: git-send-email 1.7.7.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org expand_stack() runs with a shared mmap_sem lock. Because of this, there could be multiple concurrent stack expansions in the same mm, which may cause problems in the vma gap update code. I propose to solve this by taking the mm->page_table_lock around such vma expansions, in order to avoid the concurrency issue. We only have to worry about concurrent expand_stack() calls here, since we hold a shared mmap_sem lock and all vma modificaitons other than expand_stack() are done under an exclusive mmap_sem lock. I previously tried to achieve the same effect by making sure all growable vmas in a given mm would share the same anon_vma, which we already lock here. However this turned out to be difficult - all of the schemes I tried for refcounting the growable anon_vma and clearing turned out ugly. So, I'm now proposing only the minimal fix. Signed-off-by: Michel Lespinasse --- mm/mmap.c | 14 ++++++++++++++ 1 files changed, 14 insertions(+), 0 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index 9ed3a06242a0..e44fe876a7e3 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2069,6 +2069,11 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address) if (vma->vm_pgoff + (size >> PAGE_SHIFT) >= vma->vm_pgoff) { error = acct_stack_growth(vma, size, grow); if (!error) { + /* + * page_table_lock to protect against + * concurrent vma expansions + */ + spin_lock(&vma->vm_mm->page_table_lock); anon_vma_interval_tree_pre_update_vma(vma); vma->vm_end = address; anon_vma_interval_tree_post_update_vma(vma); @@ -2076,6 +2081,8 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address) vma_gap_update(vma->vm_next); else vma->vm_mm->highest_vm_end = address; + spin_unlock(&vma->vm_mm->page_table_lock); + perf_event_mmap(vma); } } @@ -2126,11 +2133,18 @@ int expand_downwards(struct vm_area_struct *vma, if (grow <= vma->vm_pgoff) { error = acct_stack_growth(vma, size, grow); if (!error) { + /* + * page_table_lock to protect against + * concurrent vma expansions + */ + spin_lock(&vma->vm_mm->page_table_lock); anon_vma_interval_tree_pre_update_vma(vma); vma->vm_start = address; vma->vm_pgoff -= grow; anon_vma_interval_tree_post_update_vma(vma); vma_gap_update(vma); + spin_unlock(&vma->vm_mm->page_table_lock); + perf_event_mmap(vma); } } -- 1.7.7.3