From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751884Ab3LXIu5 (ORCPT ); Tue, 24 Dec 2013 03:50:57 -0500 Received: from mail.linux-iscsi.org ([67.23.28.174]:59326 "EHLO linux-iscsi.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751299Ab3LXIu4 (ORCPT ); Tue, 24 Dec 2013 03:50:56 -0500 Message-ID: <1387875122.5567.241.camel@haakon3.risingtidesystems.com> Subject: Re: bio_integrity_verify() bug causing READ verify to be silently skipped From: "Nicholas A. Bellinger" To: "Martin K. Petersen" Cc: linux-scsi , LKML , Jens Axboe , Christoph Hellwig , Hannes Reinecke , James Bottomley , kmo@daterainc.com Date: Tue, 24 Dec 2013 00:52:02 -0800 In-Reply-To: <1387858826.5567.236.camel@haakon3.risingtidesystems.com> References: <1387858826.5567.236.camel@haakon3.risingtidesystems.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.4.4-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2013-12-23 at 20:20 -0800, Nicholas A. Bellinger wrote: > Hi Martin & Co, > > So after playing with the mainline DIF client against an initial WIP > target DIF support patch, I've started hitting a bug in > bio_integrity_verify() that causes READ verify logic to be silently > skipped for both WIP target and existing scsi_debug DIF code. > > The issue is with the scsi_end_request() -> blk_end_request() completion > path, where eventually blk_update_request() -> req_bio_endio() -> > bio_advance() is called to increment bio->bi_idx to a non-zero value. > > Given that bio_integrity_verify() is using bio_for_each_segment(), the > loop starts from the updated bio->bi_idx, and not a zero value, which > ends up skipping individual bio segment calls to bi->verify_fn(). > > The following patch changes bio_integrity_verify() to use > bio_for_each_segment_all() instead of bio_for_each_segment() to ensure > that the segment walk always starts from zero, regardless of the current > bio->bi_idx value after bio_advance(). > > Note this bug has been observed with v3.13-rc3 code, and I haven't yet > looked back to figure out when this bug was first introduced.. Any > ideas..? So the commit that introduced bio_advance() into req_bio_endio() code was: commit f79ea4161434b31e351658283b24e92c3e570142 Author: Kent Overstreet Date: Thu Sep 20 16:38:30 2012 -0700 block: Refactor blk_update_request() So AFAICT this has been broken since v3.10.. (CC'ing kmo) --nab > > Interestingly enough, the scsi-mq alpha code does not suffer from this > bug, as blk_end_request() is never called from scsi_mq_end_request() -> > blk_mq_end_io() completion path code. > > Thank you, > > --nab > > From 32242942edca095e8dd126cb1408f2842340773e Mon Sep 17 00:00:00 2001 > From: Nicholas Bellinger > Date: Tue, 24 Dec 2013 04:00:24 +0000 > Subject: [PATCH] bio-integrity: Fix bio_integrity_verify segment start bug > > This patch addresses a bug in bio_integrity_verify() code that has > been causing DIF READ verify operations to be silently skipped. > > The issue is that bio->bi_idx will have been incremented within > bio_advance() code in the normal blk_update_request() -> > req_bio_endio() completion path, and bio_integrity_verify() is > using bio_for_each_segment() which starts the bio segment walk > at the current bio->bi_idx. > > So instead use bio_for_each_segment_all() to always start the bio > segment walk from zero, regardless of the current bio->bi_idx > value after bio_advance() has been called. > > Cc: Martin K. Petersen > Cc: Jens Axboe > Cc: Christoph Hellwig > Signed-off-by: Nicholas Bellinger > --- > fs/bio-integrity.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/bio-integrity.c b/fs/bio-integrity.c > index fc60b31..f1d5cde 100644 > --- a/fs/bio-integrity.c > +++ b/fs/bio-integrity.c > @@ -450,7 +450,7 @@ static int bio_integrity_verify(struct bio *bio) > bix.disk_name = bio->bi_bdev->bd_disk->disk_name; > bix.sector_size = bi->sector_size; > > - bio_for_each_segment(bv, bio, i) { > + bio_for_each_segment_all(bv, bio, i) { > void *kaddr = kmap_atomic(bv->bv_page); > bix.data_buf = kaddr + bv->bv_offset; > bix.data_size = bv->bv_len;