From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with ESMTP id 7DE066B01F1 for ; Thu, 26 Aug 2010 06:54:34 -0400 (EDT) Received: from hpaq12.eem.corp.google.com (hpaq12.eem.corp.google.com [172.25.149.12]) by smtp-out.google.com with ESMTP id o7QAsTU8011283 for ; Thu, 26 Aug 2010 03:54:31 -0700 Received: from vws16 (vws16.prod.google.com [10.241.21.144]) by hpaq12.eem.corp.google.com with ESMTP id o7QAreLX021201 for ; Thu, 26 Aug 2010 03:54:28 -0700 Received: by vws16 with SMTP id 16so1648765vws.28 for ; Thu, 26 Aug 2010 03:54:28 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20100825.234149.189710316.davem@davemloft.net> References: <20100825.234149.189710316.davem@davemloft.net> Date: Thu, 26 Aug 2010 03:54:28 -0700 Message-ID: Subject: Re: [PATCH] mm: fix hang on anon_vma->root->lock From: Hugh Dickins Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org To: David Miller Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, riel@redhat.com, aarcange@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: 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). I _think_ that change was itself a simplification of the locking in 2.6.35, rather than plugging a particular hole (it's not been backported to -stable), but I may be wrong on that - Rik? Hugh -- 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