From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753715AbZK3KAi (ORCPT ); Mon, 30 Nov 2009 05:00:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753024AbZK3KAh (ORCPT ); Mon, 30 Nov 2009 05:00:37 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:33494 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752929AbZK3KAg (ORCPT ); Mon, 30 Nov 2009 05:00:36 -0500 Date: Mon, 30 Nov 2009 05:00:41 -0500 From: Christoph Hellwig To: Linus Torvalds Cc: Nick Piggin , Linux Kernel Mailing List Subject: Re: [rfc] "fair" rw spinlocks Message-ID: <20091130100041.GA29610@infradead.org> References: <20091123145409.GA29627@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.19 (2009-01-05) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Nov 28, 2009 at 09:30:18AM -0800, Linus Torvalds wrote: > > > On Mon, 23 Nov 2009, Nick Piggin wrote: > > > > Last time this issue came up that I could see, I don't think > > there were objections to making rwlocks fair, the main > > difficulty seemed to be that we allow reentrant read locks > > (so a write lock waiting must not block arbitrary read lockers). > > We have at least one major rwlock user - tasklist_lock or whatever. And > that one definitely depends on being able to do 'rwlock()' in an > interrupt, without other rwlock'ers having to disable irq's (even if there > might be a new writer coming in on another cpu). How long will this use be around? I've seen some slow progress toward replacing most read side uses of the task list lock with RCU. While we still have lots of read side users now I wonder when they'll go away.