From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6C9DEC43381 for ; Wed, 27 Feb 2019 01:55:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3D78C218D8 for ; Wed, 27 Feb 2019 01:55:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729645AbfB0Bxy (ORCPT ); Tue, 26 Feb 2019 20:53:54 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40332 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729364AbfB0Bxy (ORCPT ); Tue, 26 Feb 2019 20:53:54 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 83D4DC07D8D3; Wed, 27 Feb 2019 01:53:53 +0000 (UTC) Received: from ming.t460p (ovpn-8-21.pek2.redhat.com [10.72.8.21]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2C9FB6682E; Wed, 27 Feb 2019 01:53:42 +0000 (UTC) Date: Wed, 27 Feb 2019 09:53:37 +0800 From: Ming Lei To: Jens Axboe Cc: Ming Lei , Eric Biggers , "open list:AIO" , linux-block , linux-api@vger.kernel.org, Christoph Hellwig , Jeff Moyer , Avi Kivity , jannh@google.com, Al Viro Subject: Re: [PATCH 11/19] block: implement bio helper to add iter bvec pages to bio Message-ID: <20190227015336.GD16802@ming.t460p> References: <20190211190049.7888-1-axboe@kernel.dk> <20190211190049.7888-13-axboe@kernel.dk> <20190220225856.GB28313@ming.t460p> <20190226034613.GA676@sol.localdomain> <1652577e-787b-638e-625d-c200fb144a9d@kernel.dk> <09820845-07cb-5153-e1c5-59ed185db26f@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <09820845-07cb-5153-e1c5-59ed185db26f@kernel.dk> User-Agent: Mutt/1.9.1 (2017-09-22) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Wed, 27 Feb 2019 01:53:53 +0000 (UTC) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Tue, Feb 26, 2019 at 06:47:54PM -0700, Jens Axboe wrote: > On 2/26/19 6:21 PM, Ming Lei wrote: > > On Tue, Feb 26, 2019 at 11:56 PM Jens Axboe wrote: > >> > >> On 2/25/19 9:34 PM, Jens Axboe wrote: > >>> On 2/25/19 8:46 PM, Eric Biggers wrote: > >>>> Hi Jens, > >>>> > >>>> On Thu, Feb 21, 2019 at 10:45:27AM -0700, Jens Axboe wrote: > >>>>> On 2/20/19 3:58 PM, Ming Lei wrote: > >>>>>> On Mon, Feb 11, 2019 at 12:00:41PM -0700, Jens Axboe wrote: > >>>>>>> For an ITER_BVEC, we can just iterate the iov and add the pages > >>>>>>> to the bio directly. This requires that the caller doesn't releases > >>>>>>> the pages on IO completion, we add a BIO_NO_PAGE_REF flag for that. > >>>>>>> > >>>>>>> The current two callers of bio_iov_iter_get_pages() are updated to > >>>>>>> check if they need to release pages on completion. This makes them > >>>>>>> work with bvecs that contain kernel mapped pages already. > >>>>>>> > >>>>>>> Reviewed-by: Hannes Reinecke > >>>>>>> Reviewed-by: Christoph Hellwig > >>>>>>> Signed-off-by: Jens Axboe > >>>>>>> --- > >>>>>>> block/bio.c | 59 ++++++++++++++++++++++++++++++++------- > >>>>>>> fs/block_dev.c | 5 ++-- > >>>>>>> fs/iomap.c | 5 ++-- > >>>>>>> include/linux/blk_types.h | 1 + > >>>>>>> 4 files changed, 56 insertions(+), 14 deletions(-) > >>>>>>> > >>>>>>> diff --git a/block/bio.c b/block/bio.c > >>>>>>> index 4db1008309ed..330df572cfb8 100644 > >>>>>>> --- a/block/bio.c > >>>>>>> +++ b/block/bio.c > >>>>>>> @@ -828,6 +828,23 @@ int bio_add_page(struct bio *bio, struct page *page, > >>>>>>> } > >>>>>>> EXPORT_SYMBOL(bio_add_page); > >>>>>>> > >>>>>>> +static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter) > >>>>>>> +{ > >>>>>>> + const struct bio_vec *bv = iter->bvec; > >>>>>>> + unsigned int len; > >>>>>>> + size_t size; > >>>>>>> + > >>>>>>> + len = min_t(size_t, bv->bv_len, iter->count); > >>>>>>> + size = bio_add_page(bio, bv->bv_page, len, > >>>>>>> + bv->bv_offset + iter->iov_offset); > >>>>>> > >>>>>> iter->iov_offset needs to be subtracted from 'len', looks > >>>>>> the following delta change[1] is required, otherwise memory corruption > >>>>>> can be observed when running xfstests over loop/dio. > >>>>> > >>>>> Thanks, I folded this in. > >>>>> > >>>>> -- > >>>>> Jens Axboe > >>>>> > >>>> > >>>> syzkaller started hitting a crash on linux-next starting with this commit, and > >>>> it still occurs even with your latest version that has Ming's fix folded in. > >>>> Specifically, commit a566653ab5ab80a from your io_uring branch with commit date > >>>> Sun Feb 24 08:20:53 2019 -0700. > >>>> > >>>> Reproducer: > >>>> > >>>> #define _GNU_SOURCE > >>>> #include > >>>> #include > >>>> #include > >>>> #include > >>>> #include > >>>> #include > >>>> > >>>> int main(void) > >>>> { > >>>> int memfd, loopfd; > >>>> > >>>> memfd = syscall(__NR_memfd_create, "foo", 0); > >>>> > >>>> pwrite(memfd, "\xa8", 1, 4096); > >>>> > >>>> loopfd = open("/dev/loop0", O_RDWR|O_DIRECT); > >>>> > >>>> ioctl(loopfd, LOOP_SET_FD, memfd); > >>>> > >>>> sendfile(loopfd, loopfd, NULL, 1000000); > >>>> } > >>>> > >>>> > >>>> Crash: > >>>> > >>>> page:ffffea0001a6aab8 count:0 mapcount:0 mapping:0000000000000000 index:0x0 > >>>> flags: 0x100000000000000() > >>>> raw: 0100000000000000 ffffea0001ad2c50 ffff88807fca49d0 0000000000000000 > >>>> raw: 0000000000000000 0000000000000000 00000000ffffffff > >>>> page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 0) > >>> > >>> I see what this is, I'll cut a fix for this tomorrow. > >> > >> Folded in a fix for this, it's in my current io_uring branch and my for-next > >> branch. > > > > Hi Jens, > > > > I saw the following change is added: > > > > + if (size == len) { > > + /* > > + * For the normal O_DIRECT case, we could skip grabbing this > > + * reference and then not have to put them again when IO > > + * completes. But this breaks some in-kernel users, like > > + * splicing to/from a loop device, where we release the pipe > > + * pages unconditionally. If we can fix that case, we can > > + * get rid of the get here and the need to call > > + * bio_release_pages() at IO completion time. > > + */ > > + get_page(bv->bv_page); > > > > Now the 'bv' may point to more than one page, so the following one may be > > needed: > > > > int i; > > struct bvec_iter_all iter_all; > > struct bio_vec *tmp; > > > > mp_bvec_for_each_segment(tmp, bv, i, iter_all) > > get_page(tmp->bv_page); > > I guess that would be the safest, even if we don't currently have more > than one page in there. I'll fix it up. It is easy to see multipage bvec from loop, :-) Thanks, Ming