Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755159AbYHDRrX (ORCPT ); Mon, 4 Aug 2008 13:47:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751552AbYHDRrH (ORCPT ); Mon, 4 Aug 2008 13:47:07 -0400 Received: from host36-195-149-62.serverdedicati.aruba.it ([62.149.195.36]:37438 "EHLO mx.cpushare.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751351AbYHDRrF (ORCPT ); Mon, 4 Aug 2008 13:47:05 -0400 Date: Mon, 4 Aug 2008 19:46:59 +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: Re: [RFC][PATCH 7/7] lockdep: spin_lock_nest_lock() Message-ID: <20080804174659.GK11476@duo.random> References: <20080804131012.246115111@chello.nl> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080804172728.GJ11476@duo.random> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2169 Lines: 62 From: Andrea Arcangeli Lockdep can't recognize if spinlocks are at a different address. So trylock avoids lockdep to generate false positives. After lockdep will be fixed this change can and should be reverted. Signed-off-by: Andrea Arcangeli --- On Mon, Aug 04, 2008 at 07:27:28PM +0200, Andrea Arcangeli wrote: > I can reproduce this now yes after a 'make sync'. (btw it's not like I forgot to sync, but I sync against the wrong source tree previously because it was in the bash history, it's a bit complicate to explain) > I assume it can't understand the spinlock address is different (I > think it uses the address as key only for static locks), so I wonder > if you could call print_deadlock_bug() from the failure path of the > spinlock to solve this? In the meantime (as I doubt lockdep will get fixed any time soon) this will workaround it. 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 19:41:53 2008 +0200 @@ -2279,8 +2279,13 @@ 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 can't + * differentiate between the 'mapping' 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 +2315,13 @@ 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 can't + * differentiate between 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/