From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753384Ab0HZS7t (ORCPT ); Thu, 26 Aug 2010 14:59:49 -0400 Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:34947 "EHLO sunset.davemloft.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751886Ab0HZS7r (ORCPT ); Thu, 26 Aug 2010 14:59:47 -0400 Date: Thu, 26 Aug 2010 12:00:02 -0700 (PDT) Message-Id: <20100826.120002.59671031.davem@davemloft.net> To: hughd@google.com Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, riel@redhat.com, aarcange@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] mm: fix hang on anon_vma->root->lock From: David Miller In-Reply-To: References: <20100825.234149.189710316.davem@davemloft.net> X-Mailer: Mew version 6.3 on Emacs 23.1 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Hugh Dickins Date: Thu, 26 Aug 2010 03:54:28 -0700 > On Wed, Aug 25, 2010 at 11:41 PM, David Miller wrote: >> From: Hugh Dickins >> Date: Wed, 25 Aug 2010 23:12:54 -0700 (PDT) >> >>> After several hours, kbuild tests hang with anon_vma_prepare() spinning on >>> a newly allocated anon_vma's lock - on a box with CONFIG_TREE_PREEMPT_RCU=y >>> (which makes this very much more likely, but it could happen without). >>> >>> The ever-subtle page_lock_anon_vma() now needs a further twist: since >>> anon_vma_prepare() and anon_vma_fork() are liable to change the ->root >>> of a reused anon_vma structure at any moment, page_lock_anon_vma() >>> needs to check page_mapped() again before succeeding, otherwise >>> page_unlock_anon_vma() might address a different root->lock. >>> >>> Signed-off-by: Hugh Dickins >> >> Interesting, is the condition which allows this to trigger specific >> to this merge window or was it always possible? > > Just specific to this merge window, which started using > anon_vma->root->lock in place of anon_vma->lock (anon_vma->root is > often anon_vma itself, but not always). Ok, because I've been seeing mysterious hangs recently on one of my sparc64 boxes and I was wondering if this might explain them :-)