From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757329AbZCAPHg (ORCPT ); Sun, 1 Mar 2009 10:07:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752537AbZCAPH2 (ORCPT ); Sun, 1 Mar 2009 10:07:28 -0500 Received: from mx2.suse.de ([195.135.220.15]:45239 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752185AbZCAPH2 (ORCPT ); Sun, 1 Mar 2009 10:07:28 -0500 Date: Sun, 1 Mar 2009 16:07:25 +0100 From: Nick Piggin To: Wu Fengguang Cc: linux-kernel@vger.kernel.org, Pekka Enberg Subject: Re: recursive slqb_lock Message-ID: <20090301150725.GB26905@wotan.suse.de> References: <20090226053450.GA31108@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090226053450.GA31108@localhost> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 26, 2009 at 01:34:50PM +0800, Wu Fengguang wrote: > Hi Nick, > > I got a lockdep warning. It looks like the slqb_lock will be taken > twice in the call chain: > > s_start() => take slqb_lock > s_show() > gather_stats() => take slqb_lock again Hey, thanks for this. The following patch should fix it. -- Fix the lockdep error reported by Fengguang where down_read slqb_lock is taken twice, with the possibility for a deadlock. Signed-off-by: Nick Piggin --- Index: linux-2.6/mm/slqb.c =================================================================== --- linux-2.6.orig/mm/slqb.c 2009-03-02 02:05:16.000000000 +1100 +++ linux-2.6/mm/slqb.c 2009-03-02 02:05:45.000000000 +1100 @@ -3079,7 +3079,9 @@ static void __gather_stats(void *arg) spin_unlock(&gather->lock); } -static void gather_stats(struct kmem_cache *s, struct stats_gather *stats) +/* must be called with slqb_lock held */ +static void gather_stats_locked(struct kmem_cache *s, + struct stats_gather *stats) { #ifdef CONFIG_NUMA int node; @@ -3089,8 +3091,6 @@ static void gather_stats(struct kmem_cac stats->s = s; spin_lock_init(&stats->lock); - down_read(&slqb_lock); /* hold off hotplug */ - on_each_cpu(__gather_stats, stats, 1); #ifdef CONFIG_NUMA @@ -3119,10 +3119,15 @@ static void gather_stats(struct kmem_cac } #endif - up_read(&slqb_lock); - stats->nr_objects = stats->nr_slabs * s->objects; } + +static void gather_stats(struct kmem_cache *s, struct stats_gather *stats) +{ + down_read(&slqb_lock); /* hold off hotplug */ + gather_stats(s, stats); + up_read(&slqb_lock); +} #endif /* @@ -3175,7 +3180,7 @@ static int s_show(struct seq_file *m, vo s = list_entry(p, struct kmem_cache, list); - gather_stats(s, &stats); + gather_stats_locked(s, &stats); seq_printf(m, "%-17s %6lu %6lu %6u %4u %4d", s->name, stats.nr_inuse, stats.nr_objects, s->size, s->objects, (1 << s->order));