Return-path: Received: from e2.ny.us.ibm.com ([32.97.182.142]:42013 "EHLO e2.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760693AbYHAVKp (ORCPT ); Fri, 1 Aug 2008 17:10:45 -0400 Date: Fri, 1 Aug 2008 14:10:43 -0700 From: "Paul E. McKenney" To: Nick Piggin Cc: Miklos Szeredi , peterz@infradead.org, davem@davemloft.net, jarkao2@gmail.com, Larry.Finger@lwfinger.net, kaber@trash.net, torvalds@linux-foundation.org, akpm@linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-wireless@vger.kernel.org, mingo@redhat.com Subject: Re: Kernel WARNING: at net/core/dev.c:1330 __netif_schedule+0x2c/0x98() Message-ID: <20080801211043.GW14851@linux.vnet.ibm.com> (sfid-20080801_231106_921319_32D84A61) Reply-To: paulmck@linux.vnet.ibm.com References: <1216890648.7257.258.camel@twins> <200807242038.36693.nickpiggin@yahoo.com.au> <200807242106.52672.nickpiggin@yahoo.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <200807242106.52672.nickpiggin@yahoo.com.au> Sender: linux-wireless-owner@vger.kernel.org List-ID: On Thu, Jul 24, 2008 at 09:06:51PM +1000, Nick Piggin wrote: > On Thursday 24 July 2008 20:55, Miklos Szeredi wrote: > > On Thu, 24 Jul 2008, Nick Piggin wrote: > > > Hey, something kind of cool (and OT) I've just thought of that we can > > > do with ticket locks is to take tickets for 2 (or 64K) nested locks, > > > and then wait for them both (all), so the cost is N*lock + longest spin, > > > rather than N*lock + N*avg spin. > > > > Isn't this deadlocky? > > > > E.g. one task takes ticket x=1, then other task comes in and takes x=2 > > and y=1, then first task takes y=2. Then neither can actually > > complete both locks. > > Oh duh of course you still need mutual exclusion from the first lock > to order the subsequent :P > > So yeah it only works for N > 2 locks, and you have to spin_lock the > first one... so unsuitable for scheduler. Or sort the locks by address or some such. Thanx, Paul