From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752022AbaE0LZN (ORCPT ); Tue, 27 May 2014 07:25:13 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42207 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750904AbaE0LZJ (ORCPT ); Tue, 27 May 2014 07:25:09 -0400 Date: Tue, 27 May 2014 13:24:59 +0200 From: Maurizio Lombardi To: Ming Lei Cc: Jens Axboe , jet.chen@intel.com, Stephen Rothwell , LKML , lkp@01.org, Fengguang Wu Subject: Re: [jet.chen@intel.com: [bio] kernel BUG at drivers/block/virtio_blk.c:166!] Message-ID: <20140527112459.GF2205@dhcp-27-189.brq.redhat.com> References: <20140526194347.GB2271@dhcp-27-189.brq.redhat.com> <20140527084359.GD2205@dhcp-27-189.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140527084359.GD2205@dhcp-27-189.brq.redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 27, 2014 at 10:43:59AM +0200, Maurizio Lombardi wrote: > > But now I'm suspicious of this part of commit 3979ef4dcf: > > failed: > bvec->bv_page = NULL; > bvec->bv_len = 0; > bvec->bv_offset = 0; > bio->bi_vcnt--; <---------------- > blk_recount_segments(q, bio); > return 0; > > Is decreasing bi_vcnt sufficient to guarantee that blk_recount_segments() > recalculates the correct number of physical segments? > Looking at the __blk_recalc_rq_segments() it appears it may not be the case. > > The question is how can we restore the correct number of physical segments in case > of failure without breaking anything... > If my hypothesis is correct, the following patch should trigger a kernel panic, Jet Chen, can you try it and let me know whether the BUG_ON is hit or not? diff --git a/block/bio.c b/block/bio.c index 0443694..763868f 100644 --- a/block/bio.c +++ b/block/bio.c @@ -701,6 +701,7 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page unsigned int max_sectors) { int retried_segments = 0; + unsigned int phys_segments_orig; struct bio_vec *bvec; /* @@ -751,6 +752,9 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page if (bio->bi_vcnt >= bio->bi_max_vecs) return 0; + blk_recount_segments(q, bio); + phys_segments_orig = bio->bi_phys_segments; + /* * setup the new entry, we might clear it again later if we * cannot add the page @@ -811,6 +815,7 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page bvec->bv_offset = 0; bio->bi_vcnt--; blk_recount_segments(q, bio); + BUG_ON(phys_segments_orig != bio->bi_phys_segments); return 0; } Regards, Maurizio Lombardi