From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754945Ab3KAJi3 (ORCPT ); Fri, 1 Nov 2013 05:38:29 -0400 Received: from mga09.intel.com ([134.134.136.24]:39514 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751485Ab3KAJi2 (ORCPT ); Fri, 1 Nov 2013 05:38:28 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.93,535,1378882800"; d="scan'208";a="428177879" Date: Fri, 1 Nov 2013 17:38:44 +0800 From: Yuanhan Liu To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Linus Torvalds , Andrew Morton , Rik van Riel , Michel Lespinasse Subject: Re: [PATCH 1/4] mm/rmap: per anon_vma lock Message-ID: <20131101093844.GA30123@yliu-dev.sh.intel.com> References: <1383292467-28922-1-git-send-email-yuanhan.liu@linux.intel.com> <1383292467-28922-2-git-send-email-yuanhan.liu@linux.intel.com> <20131101084329.GB19466@laptop.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131101084329.GB19466@laptop.lan> 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, Nov 01, 2013 at 09:43:29AM +0100, Peter Zijlstra wrote: > On Fri, Nov 01, 2013 at 03:54:24PM +0800, Yuanhan Liu wrote: > > @@ -497,15 +495,20 @@ static void vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root) > > * anon_vma_interval_tree_post_update_vma(). > > * > > * The entire update must be protected by exclusive mmap_sem and by > > - * the root anon_vma's mutex. > > + * the anon_vma's mutex. > > */ > > static inline void > > anon_vma_interval_tree_pre_update_vma(struct vm_area_struct *vma) > > { > > struct anon_vma_chain *avc; > > > > - list_for_each_entry(avc, &vma->anon_vma_chain, same_vma) > > - anon_vma_interval_tree_remove(avc, &avc->anon_vma->rb_root); > > + list_for_each_entry(avc, &vma->anon_vma_chain, same_vma) { > > + struct anon_vma *anon_vma = avc->anon_vma; > > + > > + anon_vma_lock_write(anon_vma); > > + anon_vma_interval_tree_remove(avc, &anon_vma->rb_root); > > + anon_vma_unlock_write(anon_vma); > > + } > > } > > > > static inline void > > @@ -513,8 +516,13 @@ anon_vma_interval_tree_post_update_vma(struct vm_area_struct *vma) > > { > > struct anon_vma_chain *avc; > > > > - list_for_each_entry(avc, &vma->anon_vma_chain, same_vma) > > - anon_vma_interval_tree_insert(avc, &avc->anon_vma->rb_root); > > + list_for_each_entry(avc, &vma->anon_vma_chain, same_vma) { > > + struct anon_vma *anon_vma = avc->anon_vma; > > + > > + anon_vma_lock_write(anon_vma); > > + anon_vma_interval_tree_insert(avc, &anon_vma->rb_root); > > + anon_vma_unlock_write(anon_vma); > > + } > > } > > > > static int find_vma_links(struct mm_struct *mm, unsigned long addr, > > @@ -781,7 +789,6 @@ again: remove_next = 1 + (end > next->vm_end); > > if (anon_vma) { > > VM_BUG_ON(adjust_next && next->anon_vma && > > anon_vma != next->anon_vma); > > - anon_vma_lock_write(anon_vma); > > anon_vma_interval_tree_pre_update_vma(vma); > > if (adjust_next) > > anon_vma_interval_tree_pre_update_vma(next); > > @@ -845,7 +852,6 @@ again: remove_next = 1 + (end > next->vm_end); > > anon_vma_interval_tree_post_update_vma(vma); > > if (adjust_next) > > anon_vma_interval_tree_post_update_vma(next); > > - anon_vma_unlock_write(anon_vma); > > } > > if (mapping) > > mutex_unlock(&mapping->i_mmap_mutex); > > AFAICT this isn't correct at all. We used to protect the vma interval > tree with the root lock, now we don't. We still use lock to protect anon_vma interval tree, but we lock our own interval tree this time. > All we've got left is the > mmap_sem, but anon_vma chains can cross address-spaces and thus we're up > some creek without no paddle. Yep, however, you still need acquire the address-space crossed anon_vma's lock to modify something. Say, here is a chart: http://people.freedesktop.org/~yliu/anon_vma.png. Let's take the 3rd chart as example. And assume we will unlink vma C. And the steps are: - lock c, and remove avc between c and C - lock b, and remove avc between b and C - lock a, and remove avc between a and C Thanks. --yliu