Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932260AbYBGTc2 (ORCPT ); Thu, 7 Feb 2008 14:32:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757515AbYBGTcU (ORCPT ); Thu, 7 Feb 2008 14:32:20 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:36509 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756319AbYBGTcT (ORCPT ); Thu, 7 Feb 2008 14:32:19 -0500 Date: Thu, 7 Feb 2008 20:31:40 +0100 From: Ingo Molnar To: Linus Torvalds Cc: Jens Axboe , linux-kernel@vger.kernel.org, Alan.Brunelle@hp.com, arjan@linux.intel.com, dgc@sgi.com, npiggin@suse.de, Andrew Morton , Vegard Nossum , Pekka Enberg Subject: Re: [patch] block layer: kmemcheck fixes Message-ID: <20080207193140.GA19949@elte.hu> References: <1202375945-29525-1-git-send-email-jens.axboe@oracle.com> <1202375945-29525-5-git-send-email-jens.axboe@oracle.com> <20080207100738.GB7716@elte.hu> <20080207101727.GE15220@kernel.dk> <20080207102534.GB16735@elte.hu> <20080207103136.GG15220@kernel.dk> <20080207104901.GF16735@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2439 Lines: 73 * Linus Torvalds wrote: > On Thu, 7 Feb 2008, Ingo Molnar wrote: > > INIT_HLIST_NODE(&rq->hash); > > RB_CLEAR_NODE(&rq->rb_node); > > - rq->ioprio = 0; > > - rq->buffer = NULL; > > - rq->ref_count = 1; > > - rq->q = q; > > - rq->special = NULL; > > - rq->data_len = 0; > > - rq->data = NULL; > > - rq->nr_phys_segments = 0; > > - rq->sense = NULL; > > - rq->end_io = NULL; > > - rq->end_io_data = NULL; > > - rq->completion_data = NULL; > > - rq->next_rq = NULL; > > + rq->completion_data = NULL; > > + /* rq->elevator_private */ > > + /* rq->elevator_private2 */ > > + /* rq->rq_disk */ > > + /* rq->start_time */ > > + rq->nr_phys_segments = 0; > > + /* rq->nr_hw_segments */ > > + rq->ioprio = 0; > > + rq->special = NULL; > > + rq->buffer = NULL; > ... > > Can we please just stop doing these one-by-one assignments, and just do > something like > > memset(rq, 0, sizeof(*rq)); > rq->q = q; > rq->ref_count = 1; > INIT_HLIST_NODE(&rq->hash); > RB_CLEAR_NODE(&rq->rb_node); > > instead? > > The memset() is likely faster and smaller than one-by-one assignments > anyway, even if the one-by-ones can avoid initializing some field or > there ends up being a double initialization.. i definitely agree and do that for all code i write. But if someone does item by item initialization for some crazy performance reason (networking folks tend to have such constructs), it should be done i think how i've done it in the patch: by systematically listing _every_ field in the structure, in the same order, and indicating it clearly when it is not initialized and why. and there it already shows that we do not initialize a few other members that could cause problems later on: + rq->data_len = 0; + /* rq->sense_len */ + rq->data = NULL; + rq->sense = NULL; why is sense_len not initialized - while data_len is? In any case, these days the memclear instructions are dirt cheap and we should just always initialize everything to zero by default, especially if it's almost all zero-initialized anyway. Ingo -- 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/