From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422639AbWGNQsT (ORCPT ); Fri, 14 Jul 2006 12:48:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161268AbWGNQsS (ORCPT ); Fri, 14 Jul 2006 12:48:18 -0400 Received: from py-out-1112.google.com ([64.233.166.179]:55462 "EHLO py-out-1112.google.com") by vger.kernel.org with ESMTP id S1161267AbWGNQsQ (ORCPT ); Fri, 14 Jul 2006 12:48:16 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=VJO7fccKaryeB6CXeh/sfT4ZZeRQYy90uD1SRDezfSSPprBxU7NdTAdP8aGSqq6LZNPx/NCz8blRSk4OvvWBn3qt67Xw7wA4+8iU0WBQr8YTD6IkmobN/FqQTpfWwysPuEy0eNi4W9l0IDteYGedQQFrJuawhYPXZIGkFl44VOg= Message-ID: <35f686220607140948g2b0eab42i8c2f182e729cc8e1@mail.gmail.com> Date: Fri, 14 Jul 2006 09:48:15 -0700 From: "Alok kataria" To: "Christoph Lameter" Subject: Re: [patch] lockdep: annotate mm/slab.c Cc: "Andrew Morton" , arjan@infradead.org, torvalds@osdl.org, penberg@cs.helsinki.fi, mingo@elte.hu, sekharan@us.ibm.com, linux-kernel@vger.kernel.org, nagar@watson.ibm.com, balbir@in.ibm.com, alok.kataria@calsoftinc.com, kiran@scalex86.com In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <1152763195.11343.16.camel@linuxchandra> <1152818472.3024.75.camel@laptopd505.fenrus.org> <20060713161620.f61d2ac0.akpm@osdl.org> <20060713200234.d30cf1b8.akpm@osdl.org> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On 7/13/06, Christoph Lameter wrote: > On Thu, 13 Jul 2006, Christoph Lameter wrote: > > > The fix by removing the dropping of the lock in free_block could cause > > retaking the list_lock that we already hold in the OFF_SLAB case (even in > > the non NUMA case). > > That retaking only occurs if the general slab cache used for the cache > management is the same general slab where we are freeing from. > > Otherwise we are acquiring the list_locks of two distinct slab caches There can be a _theoretical_ case in which we have a cache (X) which has its slab descriptor from another cache (Y), and this caches slab descriptor too comes from another cache (Z) ...and so on. In this case there can be a recursive lock issue. But _practically_ speaking i don't think this nesting of slab-descriptors can go down till a depth greater than 2 (because slab-descriptors come from a array-size cache, and getting a slab descriptor which has size greater than 1K is very rare). And this thing forming a cycle is virtually impossible. > which may introduce an issue of lock ordering. > > So reversing the patch seems to be the right measure after all. But we > have the two weird locking scenarios above. Yes that is the easiest way out, but let me give it a second thought. Thanks & Regards, Alok > - > 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/ > -- A computer scientist is someone who, when told to "Go to Hell," sees the "go to," rather than the destination, as harmful. Alok Kataria