Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422850AbWJPTYJ (ORCPT ); Mon, 16 Oct 2006 15:24:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1422854AbWJPTYJ (ORCPT ); Mon, 16 Oct 2006 15:24:09 -0400 Received: from server99.tchmachines.com ([72.9.230.178]:3800 "EHLO server99.tchmachines.com") by vger.kernel.org with ESMTP id S1422850AbWJPTYI (ORCPT ); Mon, 16 Oct 2006 15:24:08 -0400 Date: Mon, 16 Oct 2006 12:26:15 -0700 From: Ravikiran G Thirumalai To: Andrew Morton Cc: linux-kernel@vger.kernel.org, Christoph Lameter , Alok Kataria , "Shai Fultheim (Shai@scalex86.org)" , "Benzi Galili (Benzi@ScaleMP.com)" Subject: Re: [patch] slab: Fix a cpu hotplug race condition while tuning slab cpu caches Message-ID: <20061016192615.GA3746@localhost.localdomain> References: <20061016085439.GA6651@localhost.localdomain> <20061016111511.3901be27.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20061016111511.3901be27.akpm@osdl.org> User-Agent: Mutt/1.4.2.1i X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - server99.tchmachines.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [0 0] / [47 12] X-AntiAbuse: Sender Address Domain - scalex86.org X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1547 Lines: 41 On Mon, Oct 16, 2006 at 11:15:11AM -0700, Andrew Morton wrote: > On Mon, 16 Oct 2006 01:54:39 -0700 > Ravikiran G Thirumalai wrote: > > The problem is obvious: we have some data (the array caches) and we have a > data structure which is used to look up that data (cpu_online_map). But > we're releasing the lock while these two things are in an inconsistent > state. > > So you could have fixed this by taking cache_chain_mutex in CPU_UP_PREPARE > and releasing it in CPU_ONLINE and CPU_UP_CANCELED. Hmm, yes. I suppose so. Maybe we can do away with other uses of lock_cpu_hotplug() in slab.c as well then! Will give it a shot. Slab locking might look uglier than what it already is though no? > > > list_for_each_entry(cachep, &cache_chain, next) { > > @@ -4087,6 +4088,7 @@ ssize_t slabinfo_write(struct file *file > > } > > } > > mutex_unlock(&cache_chain_mutex); > > + unlock_cpu_hotplug(); > > if (res >= 0) > > res = count; > > return res; > > Given that this lock_cpu_hotplug() happens at a high level I guess it'll > avoid the usual lock_cpu_hotplug() horrors and we can live with it. I > assume lockdep was enabled when you were testing this? Not when I tested it. I just retested with lockdep on and things seemed fine on a SMP. Thanks, Kiran - 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/