Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751436AbaJIR6T (ORCPT ); Thu, 9 Oct 2014 13:58:19 -0400 Received: from cantor2.suse.de ([195.135.220.15]:46716 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750918AbaJIR6K (ORCPT ); Thu, 9 Oct 2014 13:58:10 -0400 Message-ID: <5436CCAF.5040100@suse.com> Date: Thu, 09 Oct 2014 13:58:07 -0400 From: Jeff Mahoney User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Ming Lei CC: Jeff Moyer , Jens Axboe , Linux Kernel Maling List Subject: Re: [PATCH] block: copy bi_vcnt in __bio_clone_fast References: <5435C093.5070405@suse.com> <54369B13.4030004@suse.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 10/9/14, 12:13 PM, Ming Lei wrote: > On Thu, Oct 9, 2014 at 11:25 PM, Ming Lei > wrote: >> On Thu, Oct 9, 2014 at 10:26 PM, Jeff Mahoney >> wrote: >>> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 >>> >>> On 10/9/14, 9:53 AM, Jeff Moyer wrote: >>>> 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)? >>> >>> Yep. I was able to reproduce it with 3.17. I did try 0738854 >>> when I was still using 3.16 since it looked like a good >>> candidate. Neither of those patches affect the problem here. >>> bio->bi_phys_segments never gets a value set in the fast clone >>> case and that translates to req->nr_phys_segments never getting >>> properly accumulated. That might not be a problem except that >>> the NO_SG_MERGE behavior bypasses the iteration that would come >>> up with the correct value. In either case, >> >> This patch may get incorrect rq->nr_phys_segments because bio >> cloning is often used in case of I/O splitting, so could you test >> if the attached patch fixes your problem? Ah. Right. > Please ignore last patch and test the attached patch since we still > should use no sg merge to recalculate req's segments for cloned > bio. Yep, this fix works as expected. Thanks, - -Jeff - -- Jeff Mahoney SUSE Labs -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.0.19 (Darwin) iQIcBAEBAgAGBQJUNsyuAAoJEB57S2MheeWyCSoQALkgpSfaWXEV89Sg0oaVbI/b KWaHv1lLKICdkIpU+ujwsZtbxOzgwhG13CeWmLZArVvVp2eljciOdpI4vpuXVtOK 12QFj7ShLtgCt7dw/2zE8NP7tY2nAWznHhd8RXrphwM2XJ2APUVGbiUld2e+IqlI jgdFrSOOVK+ZTUlDTkxjGPD6Q5zCJ7JDZ7cN7IWQB6yu115UoCJ73j9YhpfcDkRA TZKk5/1NsCq11Gn+a5zCx9WMfauwNEeuwDFXPol8BMAK6BjucrZJjPDG2ykihuuI EWUUOdnCmXgQgpW9ARrOr7ldfJO7OYL2u9WIgoBwMl1r23ZmSvIvMKIbUFuSwPSz 8yuJpzoH4SaaEO7e2ud2+aMK88Ih1Rr2uN009WPMYn5WXeCWlCBxaLmrFN4nlu3Y Z/CoFFlhjsNr9Z7QzCv+u2SyEllA0l3/u+t3SNts4jhRReDGrEQIjs0ASvbKqNYZ +c3hgrZDwv/xL1f7hBSblwIE0DgBn1rPJBfSRkSfrLzSi103lZrBQxpjN3wtjcFK 037/BfkUuzqSTG9MAdZoVkdw/iNh0Q3qfC7PjcT/EDKn4g30+DE04Sh6gDyojyvu Z0HtRYUPjnlH0OBzvK8AyXmzLoEjkiyL4rSie1F2cy+qK/uRCUjyon8oCK9nfrga 6KWf1kYhmEAO17mN1y6y =iDIX -----END PGP SIGNATURE----- -- 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/