Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754723AbZJKP33 (ORCPT ); Sun, 11 Oct 2009 11:29:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754350AbZJKP31 (ORCPT ); Sun, 11 Oct 2009 11:29:27 -0400 Received: from casper.infradead.org ([85.118.1.10]:57045 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753428AbZJKP31 (ORCPT ); Sun, 11 Oct 2009 11:29:27 -0400 Date: Sun, 11 Oct 2009 08:29:17 -0700 From: Arjan van de Ven To: Alan Cox Cc: John Kacur , linux-kernel@vger.kernel.org, Thomas Gleixner , Frederic Weisbecker , Ingo Molnar , Christoph Hellwig , Jonathan Corbet , Andrew Morton , Vincent Sanders , linux-scsi@vger.kernel.org Subject: Re: [PATCH RFC] [PATCH] drivers/scsi/ch.c: Remove BKL in ch_open Message-ID: <20091011082917.6ebbd810@infradead.org> In-Reply-To: <20091011153709.4438cf9c@lxorguk.ukuu.org.uk> References: <20091011153709.4438cf9c@lxorguk.ukuu.org.uk> Organization: Intel X-Mailer: Claws Mail 3.7.2 (GTK+ 2.16.6; i586-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.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 Content-Length: 1099 Lines: 39 On Sun, 11 Oct 2009 15:37:09 +0100 Alan Cox wrote: > On Sun, 11 Oct 2009 15:45:16 +0200 (CEST) > John Kacur wrote: > > [linux-scsi cc'd] > > > Locking in ch_open is covered by the spin_lock, it serializes the > > calls to idr_find and scsi_device_get. The BKL appears redundant to > > me here. > > I'm not so sure. In fact there are some quite umm interesting > questions about this code, and some of them are shared with other > modules too. > > Consider the following sequence > > CPU1 CPU2 > register_chrdev > ok > open device > takes lock but open does not take the BKL, so the BKL is not protecting you at all against this.. -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org -- 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/