From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tao Ma Subject: Re: [PATCH] block: fix blk_queue_end_tag() Date: Wed, 21 Dec 2011 16:16:46 +0800 Message-ID: <4EF195EE.9010409@tao.ma> References: <20111220233117.17757.71139.stgit@localhost6.localdomain6> <4EF17DC4.5010008@tao.ma> <4EF18129.7030407@tao.ma> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from oproxy7-pub.bluehost.com ([67.222.55.9]:49974 "HELO oproxy7-pub.bluehost.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752414Ab1LUIQu (ORCPT ); Wed, 21 Dec 2011 03:16:50 -0500 In-Reply-To: Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: "Williams, Dan J" Cc: Meelis Roos , axboe@kernel.dk, Tao Ma , Linux Kernel list , linux-scsi@vger.kernel.org, Ed Nadolski On 12/21/2011 03:30 PM, Williams, Dan J wrote: > On Tue, Dec 20, 2011 at 10:48 PM, Tao Ma wrote: >> On 12/21/2011 02:36 PM, Meelis Roos wrote: >>>>> - if (unlikely(tag >= bqt->max_depth)) { >>>>> + if (WARN_ONCE(tag >= bqt->real_max_depth, >>>>> + "%s: tag %d greater than tag map size: %d\n", >>>>> + __func__, tag, bqt->real_max_depth)) { >>>>> /* >>>>> * This can happen after tag depth has been reduced. >>>> Please also change the comments here since it should never happen in the >>>> right workload. >>> >>> What do you mean by right workload? Normal workload? >> yeah, so real_max_depth is the maximum depth we ever have. So in normal >> case(shrinking queue depth is also a normal user case), we should never >> arrive here. In another word, if tag >= real_max_depth, we should have a >> bug in the kernel. > > So this is what Ed Nadolski suggested, just cut to the chase and do, > the following. Seems like the comment is what got us into trouble in > the first place. > > diff --git a/block/blk-tag.c b/block/blk-tag.c > index e74d6d1..e297d9d7 100644 > --- a/block/blk-tag.c > +++ b/block/blk-tag.c > @@ -284,16 +284,7 @@ void blk_queue_end_tag(struct request_queue *q, > struct request *rq) > struct blk_queue_tag *bqt = q->queue_tags; > int tag = rq->tag; > > - BUG_ON(tag == -1); > - > - if (unlikely(tag >= bqt->max_depth)) { > - /* > - * This can happen after tag depth has been reduced. > - * But tag shouldn't be larger than real_max_depth. > - */ > - WARN_ON(tag >= bqt->real_max_depth); > - return; > - } > + BUG_ON(tag == -1 || tag > bqt->real_max_depth); I guess tag = bqt->real_max_depth should also be a problem. Thanks Tao