From patchwork Thu Apr 25 10:28:46 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Bob Liu X-Patchwork-Id: 10916771 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 3784C1575 for ; Thu, 25 Apr 2019 10:32:42 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 27D0728C33 for ; Thu, 25 Apr 2019 10:32:42 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 1B91128C5E; Thu, 25 Apr 2019 10:32:42 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI, UNPARSEABLE_RELAY autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 84B6428C33 for ; Thu, 25 Apr 2019 10:32:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726266AbfDYKck (ORCPT ); Thu, 25 Apr 2019 06:32:40 -0400 Received: from userp2120.oracle.com ([156.151.31.85]:59028 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730384AbfDYKck (ORCPT ); Thu, 25 Apr 2019 06:32:40 -0400 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x3PAIvWE004073; Thu, 25 Apr 2019 10:32:11 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=mime-version : message-id : date : from : to : cc : subject : content-type : content-transfer-encoding; s=corp-2018-07-02; bh=xdANYl6fSEzdzL4N5hz6RPXEDgzV2XxjUIiPRhSj/Zk=; b=fEX4myZIq7NifUaGFhJP5zWMLy8F2m8ejq1iRwlG5ZbeD9XBV90idrQecsI7Hlc33WE8 23Zpkd6mDNuLS0cga+5fwQRr9jQwJbnvS7GOrmkaUr7SZmS/fFZqLkqY7aIto9KaJKjp g7ScKlDVqWPcOS5h/ClST/rvrzlPjQKS/DXjuKCVSv1yIby/Bb4uFwCGwLJ7ukGYaIEa 7od1bAutLglklIEldQ6VZeIeupGmU9mWG+NtU577x0Fy+N3hs8xxuIjwgX1f/pD3UV31 f9fvuNpzHLfK57tEFWNI013xihIn3+z3u8mguCA+dqk7VS0SKeBv7CN3/ixvx5oqUtWW oQ== Received: from userp3020.oracle.com (userp3020.oracle.com [156.151.31.79]) by userp2120.oracle.com with ESMTP id 2ryv2qfed5-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 25 Apr 2019 10:32:11 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x3PASl90160868; Thu, 25 Apr 2019 10:30:11 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by userp3020.oracle.com with ESMTP id 2s0dwfb05e-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 25 Apr 2019 10:30:10 +0000 Received: from abhmp0002.oracle.com (abhmp0002.oracle.com [141.146.116.8]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id x3PAU806006422; Thu, 25 Apr 2019 10:30:09 GMT Received: from localhost.localdomain (/101.95.182.98) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Thu, 25 Apr 2019 03:29:55 -0700 MIME-Version: 1.0 Message-ID: <20190425102846.28911-1-bob.liu@oracle.com> Date: Thu, 25 Apr 2019 03:28:46 -0700 (PDT) From: Bob Liu To: axboe@kernel.dk Cc: linux-block@vger.kernel.org, hare@suse.com, ming.lei@redhat.com, bvanassche@acm.org, hch@lst.de, martin.petersen@oracle.com, jinpuwang@gmail.com, rpenyaev@suse.de, Bob Liu Subject: [PATCH v4] blk-mq: fix hang caused by freeze/unfreeze sequence X-Mailer: git-send-email 2.9.5 X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9237 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904250067 X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9237 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904250067 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP The following is a description of a hang in blk_mq_freeze_queue_wait(). The hang happens on attempting to freeze a queue while another task does queue unfreeze. The root cause is an incorrect sequence of percpu_ref_resurrect() and percpu_ref_kill() and as a result those two can be swapped: CPU#0 CPU#1 ---------------- ----------------- q1 = blk_mq_init_queue(shared_tags) q2 = blk_mq_init_queue(shared_tags) blk_mq_add_queue_tag_set(shared_tags) blk_mq_update_tag_set_depth(shared_tags) list_for_each_entry() blk_mq_freeze_queue(q1) > percpu_ref_kill() > blk_mq_freeze_queue_wait() blk_cleanup_queue(q1) blk_mq_freeze_queue(q1) > percpu_ref_kill() ^^^^^^ freeze_depth can't guarantee the order blk_mq_unfreeze_queue() > percpu_ref_resurrect() > blk_mq_freeze_queue_wait() ^^^^^^ Hang here!!!! This wrong sequence raises kernel warning: percpu_ref_kill_and_confirm called more than once on blk_queue_usage_counter_release! WARNING: CPU: 0 PID: 11854 at lib/percpu-refcount.c:336 percpu_ref_kill_and_confirm+0x99/0xb0 But the most unpleasant effect is a hang of a blk_mq_freeze_queue_wait(), which waits for a zero of a q_usage_counter, which never happens because percpu-ref was reinited (instead of being killed) and stays in PERCPU state forever. How to reproduce: - "insmod null_blk.ko shared_tags=1 nr_devices=0 queue_mode=2" - cpu0: python Script.py 0; taskset the corresponding process running on cpu0 - cpu1: python Script.py 1; taskset the corresponding process running on cpu1 Script.py: ------ #!/usr/bin/python3 import os import sys while True: on = "echo 1 > /sys/kernel/config/nullb/%s/power" % sys.argv[1] off = "echo 0 > /sys/kernel/config/nullb/%s/power" % sys.argv[1] os.system(on) os.system(off) ------ This bug was first reported and fixed by Roman, previous discussion: [1] Message id: 1443287365-4244-7-git-send-email-akinobu.mita@gmail.com [2] Message id: 1443563240-29306-6-git-send-email-tj@kernel.org [3] https://patchwork.kernel.org/patch/9268199/ Signed-off-by: Bob Liu Reviewed-by: Ming Lei Reviewed-by: Bart Van Assche --- v4: - Update commit log v3: - rebase to v5.1 v2: - forgotten hunk from local repo - minor tweaks in the commit message --- block/blk-core.c | 3 ++- block/blk-mq.c | 19 ++++++++++--------- include/linux/blkdev.h | 7 ++++++- 3 files changed, 18 insertions(+), 11 deletions(-) -- 2.9.5 diff --git a/block/blk-core.c b/block/blk-core.c index a55389b..fb97497 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -433,7 +433,7 @@ int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags) smp_rmb(); wait_event(q->mq_freeze_wq, - (atomic_read(&q->mq_freeze_depth) == 0 && + (!q->mq_freeze_depth && (pm || (blk_pm_request_resume(q), !blk_queue_pm_only(q)))) || blk_queue_dying(q)); @@ -523,6 +523,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id) spin_lock_init(&q->queue_lock); init_waitqueue_head(&q->mq_freeze_wq); + mutex_init(&q->mq_freeze_lock); /* * Init percpu_ref in atomic mode so that it's faster to shutdown. diff --git a/block/blk-mq.c b/block/blk-mq.c index a935483..373af60 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -143,13 +143,14 @@ void blk_mq_in_flight_rw(struct request_queue *q, struct hd_struct *part, void blk_freeze_queue_start(struct request_queue *q) { - int freeze_depth; - - freeze_depth = atomic_inc_return(&q->mq_freeze_depth); - if (freeze_depth == 1) { + mutex_lock(&q->mq_freeze_lock); + if (++q->mq_freeze_depth == 1) { percpu_ref_kill(&q->q_usage_counter); + mutex_unlock(&q->mq_freeze_lock); if (queue_is_mq(q)) blk_mq_run_hw_queues(q, false); + } else { + mutex_unlock(&q->mq_freeze_lock); } } EXPORT_SYMBOL_GPL(blk_freeze_queue_start); @@ -198,14 +199,14 @@ EXPORT_SYMBOL_GPL(blk_mq_freeze_queue); void blk_mq_unfreeze_queue(struct request_queue *q) { - int freeze_depth; - - freeze_depth = atomic_dec_return(&q->mq_freeze_depth); - WARN_ON_ONCE(freeze_depth < 0); - if (!freeze_depth) { + mutex_lock(&q->mq_freeze_lock); + q->mq_freeze_depth--; + WARN_ON_ONCE(q->mq_freeze_depth < 0); + if (!q->mq_freeze_depth) { percpu_ref_resurrect(&q->q_usage_counter); wake_up_all(&q->mq_freeze_wq); } + mutex_unlock(&q->mq_freeze_lock); } EXPORT_SYMBOL_GPL(blk_mq_unfreeze_queue); diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 5c58a3b..64f7683 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -535,7 +535,7 @@ struct request_queue { struct mutex sysfs_lock; - atomic_t mq_freeze_depth; + int mq_freeze_depth; #if defined(CONFIG_BLK_DEV_BSG) struct bsg_class_device bsg_dev; @@ -547,6 +547,11 @@ struct request_queue { #endif struct rcu_head rcu_head; wait_queue_head_t mq_freeze_wq; + /* + * Protect concurrent access to q_usage_counter by + * percpu_ref_kill() and percpu_ref_reinit(). + */ + struct mutex mq_freeze_lock; struct percpu_ref q_usage_counter; struct list_head all_q_node;