From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763352AbZJOXp1 (ORCPT ); Thu, 15 Oct 2009 19:45:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1763339AbZJOXp1 (ORCPT ); Thu, 15 Oct 2009 19:45:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:22819 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758818AbZJOXp0 (ORCPT ); Thu, 15 Oct 2009 19:45:26 -0400 Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <1255359207.10420.31.camel@twins> References: <1255359207.10420.31.camel@twins> <4AD0A0F7.9070700@clamav.net> To: Peter Zijlstra Cc: dhowells@redhat.com, =?ISO-8859-1?Q?T=F6r=F6k?= Edwin , Ingo Molnar , Linux Kernel , aCaB , Nick Piggin , Linus Torvalds , Thomas Gleixner Subject: Re: Mutex vs semaphores scheduler bug Date: Fri, 16 Oct 2009 00:44:26 +0100 Message-ID: <24718.1255650266@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter Zijlstra wrote: > The problem appears to be that rwsem doesn't allow lock-stealing With good reason. rwsems can be read or write locked for a long time - so if readers can jump the queue on read-locked rwsems, then writer starvation is a real possibility. I carefully implemented it so that it is a strict FIFO to avoid certain problems I was having. David