Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755928AbYHDR5n (ORCPT ); Mon, 4 Aug 2008 13:57:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751934AbYHDR5g (ORCPT ); Mon, 4 Aug 2008 13:57:36 -0400 Received: from host36-195-149-62.serverdedicati.aruba.it ([62.149.195.36]:37443 "EHLO mx.cpushare.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750965AbYHDR5f (ORCPT ); Mon, 4 Aug 2008 13:57:35 -0400 Date: Mon, 4 Aug 2008 19:57:30 +0200 From: Andrea Arcangeli To: Peter Zijlstra Cc: Dave Jones , Roland Dreier , Linus Torvalds , David Miller , jeremy@goop.org, hugh@veritas.com, mingo@elte.hu, akpm@linux-foundation.org, linux-kernel@vger.kernel.org Subject: [PATCH] workaround minor lockdep bug triggered by mm_take_all_locks Message-ID: <20080804175730.GL11476@duo.random> References: <1217859571.3589.7.camel@twins> <1217860332.3589.11.camel@twins> <20080804145318.GA17867@redhat.com> <1217861763.3589.13.camel@twins> <20080804162657.GI11476@duo.random> <1217867935.3589.35.camel@twins> <20080804172728.GJ11476@duo.random> <20080804174659.GK11476@duo.random> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080804174659.GK11476@duo.random> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1832 Lines: 51 From: Andrea Arcangeli Lockdep can't recognize if spinlocks are at a different address. So using trylock in a loop is one way to avoid lockdep to generate false positives. After lockdep will be fixed this change can and should be reverted. Signed-off-by: Andrea Arcangeli --- Resubmit because I didn't update the subject and so I improved the comments too. This is mostly to show it's a bug in lockdep and it can be trivially worked around without having to fix lockdep for real, any superior solution to this hack is more than welcome and recommended. diff -r 3469dce61df1 mm/mmap.c --- a/mm/mmap.c Tue Jul 29 20:01:28 2008 +0200 +++ b/mm/mmap.c Mon Aug 04 19:54:27 2008 +0200 @@ -2279,8 +2279,12 @@ static void vm_lock_anon_vma(struct anon /* * The LSB of head.next can't change from under us * because we hold the mm_all_locks_mutex. + * + * spin_lock would confuse lockdep who doesn't notice + * the 'anon_vma' always changing address. */ - spin_lock(&anon_vma->lock); + while (!spin_trylock(&anon_vma->lock)) + cpu_relax(); /* * We can safely modify head.next after taking the * anon_vma->lock. If some other vma in this mm shares @@ -2310,7 +2314,12 @@ static void vm_lock_mapping(struct addre */ if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags)) BUG(); - spin_lock(&mapping->i_mmap_lock); + /* + * spin_lock would confuse lockdep who doesn't notice + * the 'mapping' always changing address. + */ + while (!spin_trylock(&mapping->i_mmap_lock)) + cpu_relax(); } } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/