From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750856AbWGDMws (ORCPT ); Tue, 4 Jul 2006 08:52:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750917AbWGDMws (ORCPT ); Tue, 4 Jul 2006 08:52:48 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:54994 "EHLO pentafluge.infradead.org") by vger.kernel.org with ESMTP id S1750875AbWGDMwr (ORCPT ); Tue, 4 Jul 2006 08:52:47 -0400 Subject: Re: R/W semaphore changes From: Arjan van de Ven To: David Howells Cc: Ingo Molnar , torvalds@osdl.org, akpm@osdl.org, linux-kernel@vger.kernel.org In-Reply-To: <14683.1152017262@warthog.cambridge.redhat.com> References: <14683.1152017262@warthog.cambridge.redhat.com> Content-Type: text/plain Date: Tue, 04 Jul 2006 14:52:42 +0200 Message-Id: <1152017562.3109.48.camel@laptopd505.fenrus.org> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-2.fc4) Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2006-07-04 at 13:47 +0100, David Howells wrote: > I see you've made some R/W semaphore changes... > > | /* > | * nested locking: > | */ > > This comment is inadequate. Please be more explicit about when you're allowed > to do this. > > | extern void down_read_nested(struct rw_semaphore *sem, int subclass); > | extern void down_write_nested(struct rw_semaphore *sem, int subclass); > > Please, please, please don't. R/W semaphores are _not_ permitted to nest. yet they do in places, there where there is a natural hierarchy.. > | # define down_read_nested(sem, subclass) down_read(sem) > | # define down_write_nested(sem, subclass) down_write(sem) > > This is _not_ okay. why not?