Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757261AbaJINyP (ORCPT ); Thu, 9 Oct 2014 09:54:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:29335 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751975AbaJINyG (ORCPT ); Thu, 9 Oct 2014 09:54:06 -0400 From: Jeff Moyer To: Jeff Mahoney Cc: Jens Axboe , Linux Kernel Maling List , Ming Lei Subject: Re: [PATCH] block: copy bi_vcnt in __bio_clone_fast References: <5435C093.5070405@suse.com> X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 X-PCLoadLetter: What the f**k does that mean? Date: Thu, 09 Oct 2014 09:53:58 -0400 In-Reply-To: <5435C093.5070405@suse.com> (Jeff Mahoney's message of "Wed, 08 Oct 2014 18:54:11 -0400") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jeff Mahoney writes: > Commit 05f1dd53152173 (block: add queue flag for disabling SG merging) uses > bi_vcnt to assign bio->bi_phys_segments if sg merging is disabled. When > using device mapper on top of a blk-mq device (virtio_blk in my test), > we'd end up overflowing the scatterlist in __blk_bios_map_sg. > > __bio_clone_fast copies bi_iter and bi_io_vec but not bi_vcnt, so > blk_recount_segments would report bi_phys_segments as 0. Since > rq->nr_phys_segments is 0 as well, the checks to ensure that we don't > exceed the queue's segment limit end up allowing more bios (and segments) to > attach the a request until we finally map it. That also means we > pass the BUG_ON at the beginning of virtio_queue_rq, ultimately causing > memory corruption and a crash. > > If we copy bi_vcnt in __bio_clone_fast, the bios and requests properly > report the number of segments and everything works as expected. > > Originally reported at http://bugzilla.opensuse.org/show_bug.cgi?id=888259 Hi, Jeff, Did you manage to reproduce this problem with commit 0738854 (blk-merge: fix blk_recount_segments) applied? Or perhaps with commit 200612e (dm table: propagate QUEUE_FLAG_NO_SG_MERGE)? Cheers, Jeff -- 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/