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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 2FAC6C2D0C2 for ; Fri, 3 Jan 2020 12:04:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0CC3020848 for ; Fri, 3 Jan 2020 12:04:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727523AbgACMEE (ORCPT ); Fri, 3 Jan 2020 07:04:04 -0500 Received: from szxga04-in.huawei.com ([45.249.212.190]:8665 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727577AbgACMEE (ORCPT ); Fri, 3 Jan 2020 07:04:04 -0500 Received: from DGGEMS413-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id 9BD94C65A2EB28D9A3E7; Fri, 3 Jan 2020 20:04:01 +0800 (CST) Received: from [10.173.221.193] (10.173.221.193) by DGGEMS413-HUB.china.huawei.com (10.3.19.213) with Microsoft SMTP Server id 14.3.439.0; Fri, 3 Jan 2020 20:03:54 +0800 Subject: Re: [PATCH] block: make sure last_lookup set as NULL after part deleted To: Ming Lei , Hou Tao CC: , , , , , , , References: <20191231110945.10857-1-yuyufen@huawei.com> <20200102012314.GB16719@ming.t460p> <20200103041805.GA29924@ming.t460p> <20200103081745.GA11275@ming.t460p> From: Yufen Yu Message-ID: <82c10514-aec5-0d7c-118f-32c261015c6a@huawei.com> Date: Fri, 3 Jan 2020 20:03:54 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: <20200103081745.GA11275@ming.t460p> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.173.221.193] X-CFilter-Loop: Reflected Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Hi, Ming On 2020/1/3 16:17, Ming Lei wrote: > > We may avoid that by clearing partition pointer after killing the > partition, how about the following change? > > diff --git a/block/blk-core.c b/block/blk-core.c > index 089e890ab208..79599f5fd5b7 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -1365,18 +1365,6 @@ void blk_account_io_start(struct request *rq, bool new_io) > part_stat_inc(part, merges[rw]); > } else { > part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq)); > - if (!hd_struct_try_get(part)) { > - /* > - * The partition is already being removed, > - * the request will be accounted on the disk only > - * > - * We take a reference on disk->part0 although that > - * partition will never be deleted, so we can treat > - * it as any other partition. > - */ > - part = &rq->rq_disk->part0; > - hd_struct_get(part); > - } > part_inc_in_flight(rq->q, part, rw); > rq->part = part; > } > diff --git a/block/genhd.c b/block/genhd.c > index ff6268970ddc..e3dec90b1f43 100644 > --- a/block/genhd.c > +++ b/block/genhd.c > @@ -286,17 +286,21 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector) > ptbl = rcu_dereference(disk->part_tbl); > > part = rcu_dereference(ptbl->last_lookup); > - if (part && sector_in_part(part, sector)) > + if (part && sector_in_part(part, sector) && hd_struct_try_get(part)) > return part; > > for (i = 1; i < ptbl->len; i++) { > part = rcu_dereference(ptbl->part[i]); > > if (part && sector_in_part(part, sector)) { > + if (!hd_struct_try_get(part)) > + goto exit; > rcu_assign_pointer(ptbl->last_lookup, part); > return part; > } > } > + exit: > + hd_struct_get(&disk->part0); > return &disk->part0; > } > EXPORT_SYMBOL_GPL(disk_map_sector_rcu); > diff --git a/block/partition-generic.c b/block/partition-generic.c > index 1d20c9cf213f..9ef6c13d5650 100644 > --- a/block/partition-generic.c > +++ b/block/partition-generic.c > @@ -283,8 +283,8 @@ void delete_partition(struct gendisk *disk, int partno) > if (!part) > return; > > - rcu_assign_pointer(ptbl->part[partno], NULL); > - rcu_assign_pointer(ptbl->last_lookup, NULL); > + get_device(disk_to_dev(disk)); > + > kobject_put(part->holder_dir); > device_del(part_to_dev(part)); > > @@ -296,6 +296,15 @@ void delete_partition(struct gendisk *disk, int partno) > */ > blk_invalidate_devt(part_devt(part)); > hd_struct_kill(part); > + > + /* > + * clear partition pointers after this partition is killed, then > + * IO path can't re-assign ->last_lookup any more > + */ > + rcu_assign_pointer(ptbl->part[partno], NULL); > + rcu_assign_pointer(ptbl->last_lookup, NULL); > + > + put_device(disk_to_dev(disk)); > } > This change may cannot solve follow case: disk_map_sector_rcu delete_partition disk_map_sector_rcu hd_struct_try_get(part) hd_struct_kill last_lookup = NULL; last_lookup = part call_rcu read last_lookup free() //use-after-free sector_in_part(part, sector) There is an interval between getting part and setting last_lookup in disk_map_sector_rcu(). If we kill the part and clear last_lookup at that interval, last_lookup will be re-assign again, which can cause use-after-free for readers after call_rcu. Thanks Yufen