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=-5.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 9F6ABC2D0CE for ; Fri, 3 Jan 2020 04:18:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 55BF72253D for ; Fri, 3 Jan 2020 04:18:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="dCx4EC8x" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727145AbgACESf (ORCPT ); Thu, 2 Jan 2020 23:18:35 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:42332 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726837AbgACESf (ORCPT ); Thu, 2 Jan 2020 23:18:35 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1578025113; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dRtC+ndwzy7zVbOm3E9AQ6GAvaeWJGl7xPCJ1bLcPGw=; b=dCx4EC8xAMOd7S0l8o7VDn/5Oc46nMs/LPhogB8oIIrVpYCdGSykYgQAMqn53qFeAsECQU KD13Ueou0m1XbScMkUZMpdQBk7274g7BB/SftaWhqHBlMWsivhMiv06YXt19y+0jXkIcFZ Jy0On8Uh622k9xY3sHI8LgxylfR3XYM= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-279-JYR8pVZ3PYmdjAQ-eJhjyw-1; Thu, 02 Jan 2020 23:18:26 -0500 X-MC-Unique: JYR8pVZ3PYmdjAQ-eJhjyw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D77B3182B7AE; Fri, 3 Jan 2020 04:18:24 +0000 (UTC) Received: from ming.t460p (ovpn-8-18.pek2.redhat.com [10.72.8.18]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0630D272AF; Fri, 3 Jan 2020 04:18:12 +0000 (UTC) Date: Fri, 3 Jan 2020 12:18:05 +0800 From: Ming Lei To: Hou Tao Cc: Yufen Yu , axboe@kernel.dk, linux-block@vger.kernel.org, hch@lst.de, zhengchuan@huawei.com, yi.zhang@huawei.com, paulmck@kernel.org, joel@joelfernandes.org, rcu@vger.kernel.org Subject: Re: [PATCH] block: make sure last_lookup set as NULL after part deleted Message-ID: <20200103041805.GA29924@ming.t460p> References: <20191231110945.10857-1-yuyufen@huawei.com> <20200102012314.GB16719@ming.t460p> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Fri, Jan 03, 2020 at 11:06:25AM +0800, Hou Tao wrote: > Hi, > > On 2020/1/2 9:23, Ming Lei wrote: > > On Tue, Dec 31, 2019 at 10:55:47PM +0800, Hou Tao wrote: > >> Hi, > >> > >> On 2019/12/31 19:09, Yufen Yu wrote: > >>> When delete partition executes concurrently with IOs issue, > >>> it may cause use-after-free on part in disk_map_sector_rcu() > >>> as following: > >> snip > >> > >>> > >>> diff --git a/block/genhd.c b/block/genhd.c > >>> index ff6268970ddc..39fa8999905f 100644 > >>> --- a/block/genhd.c > >>> +++ b/block/genhd.c > >>> @@ -293,7 +293,23 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector) > >>> part = rcu_dereference(ptbl->part[i]); > >>> > >>> if (part && sector_in_part(part, sector)) { > >> snip > >> > >>> rcu_assign_pointer(ptbl->last_lookup, part); > >>> + part = rcu_dereference(ptbl->part[i]); > >>> + if (part == NULL) { > >>> + rcu_assign_pointer(ptbl->last_lookup, NULL); > >>> + break; > >>> + } > >>> return part; > >>> } > >>> } > >> > >> Not ensure whether the re-read can handle the following case or not: > >> > We have written a similar test case for the following case and found out that > process C still may got the freed hd_struct pointer from process A. So > the re-read will not resolve the problem. > > >> process A process B process C > >> > >> disk_map_sector_rcu(): delete_partition(): disk_map_sector_rcu(): > >> > >> rcu_read_lock > >> > >> // need to iterate partition table > >> part[i] != NULL (1) part[i] = NULL (2) > >> smp_mb() > >> last_lookup = NULL (3) > >> call_rcu() (4) > >> last_lookup = part[i] (5) > >> > >> > >> rcu_read_lock() > >> read last_lookup return part[i] (6) > >> sector_in_part() is OK (7) > >> return part[i] (8) > >> > >> part[i] == NULL (9) > >> last_lookup = NULL (10) > >> rcu_read_unlock() (11) > >> one RCU grace period completes > >> __delete_partition() (12) > >> free hd_partition (13) > >> // use-after-free > >> hd_struct_try_get(part[i]) (14) > >> > >> * the number in the parenthesis is the sequence of events. > >> > > > > >> Maybe RCU experts can shed some light on this problem, so cc +paulmck@kernel.org, +joel@joelfernandes.org and +RCU maillist. > >> > >> If the above case is possible, maybe we can fix the problem by pinning last_lookup through increasing its ref-count > >> (the following patch is only compile tested): > >> > >> diff --git a/block/genhd.c b/block/genhd.c > >> index 6e8543ca6912..179e0056fae1 100644 > >> --- a/block/genhd.c > >> +++ b/block/genhd.c > >> @@ -279,7 +279,14 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector) > >> part = rcu_dereference(ptbl->part[i]); > >> > >> if (part && sector_in_part(part, sector)) { > >> - rcu_assign_pointer(ptbl->last_lookup, part); > >> + struct hd_struct *old; > >> + > >> + if (!hd_struct_try_get(part)) > >> + break; > >> + > >> + old = xchg(&ptbl->last_lookup, part); > >> + if (old) > >> + hd_struct_put(old); > >> return part; > >> } > >> } > >> @@ -1231,7 +1238,11 @@ static void disk_replace_part_tbl(struct gendisk *disk, > >> rcu_assign_pointer(disk->part_tbl, new_ptbl); > >> > >> if (old_ptbl) { > >> - rcu_assign_pointer(old_ptbl->last_lookup, NULL); > >> + struct hd_struct *part; > >> + > >> + part = xchg(&old_ptbl->last_lookup, NULL); > >> + if (part) > >> + hd_struct_put(part); > >> kfree_rcu(old_ptbl, rcu_head); > >> } > >> } > >> diff --git a/block/partition-generic.c b/block/partition-generic.c > >> index 98d60a59b843..441c1c591c04 100644 > >> --- a/block/partition-generic.c > >> +++ b/block/partition-generic.c > >> @@ -285,7 +285,8 @@ void delete_partition(struct gendisk *disk, int partno) > >> return; > >> > >> rcu_assign_pointer(ptbl->part[partno], NULL); > >> - rcu_assign_pointer(ptbl->last_lookup, NULL); > >> + if (cmpxchg(&ptbl->last_lookup, part, NULL) == part) > >> + hd_struct_put(part); > >> kobject_put(part->holder_dir); > >> device_del(part_to_dev(part)); > > > > IMO this approach looks good. > > > Not sure about the overhead when there are concurrent IOs on different partitions, > we will measure that. > > We have got a seemingly better solution: caching the index of last_lookup in tbl->part[] > instead of caching the pointer itself, so we can ensure the validity of returned pointer > by ensuring it's not NULL in tbl->part[] as does when last_lookup is NULL or 0. Thinking of the problem further, looks we don't need to hold ref for .last_lookup. What we need is to make sure the partition's ref is increased just before assigning .last_lookup, so how about something like the following? 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..21f4a9b8d24d 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -286,17 +286,24 @@ 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)) { + if (!hd_struct_try_get(part)) + goto exit; 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); > > > Given partition is actually protected by percpu-refcount now, I guess the > > RCU annotation for referencing ->part[partno] and ->last_lookup may not > > be necessary, together with the part->rcu_work. > > > So we will depends on the invocation of of call_rcu() on __percpu_ref_switch_mode() to > ensure the RCU readers will find part[i] is NULL before trying to increasing > the atomic ref-counter of part[i], right ? Yeah. Thanks, Ming