From patchwork Sun Sep 17 02:37:08 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 9954519 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id F1CE6601E8 for ; Sun, 17 Sep 2017 02:38:29 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id D8C61286F7 for ; Sun, 17 Sep 2017 02:38:29 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id CD52028BA9; Sun, 17 Sep 2017 02:38:29 +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=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=unavailable 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 0FA6028B9F for ; Sun, 17 Sep 2017 02:38:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751457AbdIQChb (ORCPT ); Sat, 16 Sep 2017 22:37:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56824 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751352AbdIQCha (ORCPT ); Sat, 16 Sep 2017 22:37:30 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 92B3A8763A; Sun, 17 Sep 2017 02:37:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 92B3A8763A Authentication-Results: ext-mx02.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx02.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=longman@redhat.com Received: from llong.com (ovpn-120-87.rdu2.redhat.com [10.10.120.87]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8AB5460BE7; Sun, 17 Sep 2017 02:37:27 +0000 (UTC) From: Waiman Long To: Jens Axboe , Steven Rostedt , Ingo Molnar Cc: linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, Bart Van Assche , Waiman Long Subject: [PATCH v5] blktrace: Fix potentail deadlock between delete & sysfs ops Date: Sat, 16 Sep 2017 19:37:08 -0700 Message-Id: <1505615828-6623-1-git-send-email-longman@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Sun, 17 Sep 2017 02:37:30 +0000 (UTC) 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 lockdep code had reported the following unsafe locking scenario: CPU0 CPU1 ---- ---- lock(s_active#228); lock(&bdev->bd_mutex/1); lock(s_active#228); lock(&bdev->bd_mutex); *** DEADLOCK *** The deadlock may happen when one task (CPU1) is trying to delete a partition in a block device and another task (CPU0) is accessing tracing sysfs file (e.g. /sys/block/dm-1/trace/act_mask) in that partition. The s_active isn't an actual lock. It is a reference count (kn->count) on the sysfs (kernfs) file. Removal of a sysfs file, however, require a wait until all the references are gone. The reference count is treated like a rwsem using lockdep instrumentation code. The fact that a thread is in the sysfs callback method or in the ioctl call means there is a reference to the opended sysfs or device file. That should prevent the underlying block structure from being removed. Instead of using bd_mutex in the block_device structure, the other bd_fsfreeze_mutex mutex in the block_device structure is now overloaded to protect against concurrent blktrace data access in the blktrace.c file. There is no point in adding one more mutex to the block_device structure just for blktrace. Signed-off-by: Waiman Long --- v5: - Overload the bd_fsfreeze_mutex in block_device structure for blktrace protection. v4: - Use blktrace_mutex in blk_trace_ioctl() as well. v3: - Use a global blktrace_mutex to serialize sysfs attribute accesses instead of the bd_mutex. v2: - Use READ_ONCE() and smp_store_mb() to read and write bd_deleting. - Check for signal in the mutex_trylock loops. - Use usleep() instead of schedule() for RT tasks. include/linux/fs.h | 2 +- kernel/trace/blktrace.c | 26 ++++++++++++++++++++------ 2 files changed, 21 insertions(+), 7 deletions(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index 339e737..330b572 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -448,7 +448,7 @@ struct block_device { /* The counter of freeze processes */ int bd_fsfreeze_count; - /* Mutex for freeze */ + /* Mutex for freeze and blktrace */ struct mutex bd_fsfreeze_mutex; } __randomize_layout; diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c index 2a685b4..7cd5d1d 100644 --- a/kernel/trace/blktrace.c +++ b/kernel/trace/blktrace.c @@ -648,6 +648,20 @@ int blk_trace_startstop(struct request_queue *q, int start) } EXPORT_SYMBOL_GPL(blk_trace_startstop); +/* + * When reading or writing the blktrace sysfs files, the references to the + * opened sysfs or device files should prevent the underlying block device + * from being removed. So no further delete protection is really needed. + * + * Protection from multiple readers and writers accessing blktrace data + * concurrently is still required. The bd_mutex was used for this purpose. + * That could lead to deadlock with concurrent block device deletion and + * sysfs access. Instead, the block device bd_fsfreeze_mutex is now + * overloaded for blktrace data protection. Like freeze/thaw, blktrace + * functionality is not frequently used. There is no point in adding + * one more mutex to the block_device structure just for blktrace. + */ + /** * blk_trace_ioctl: - handle the ioctls associated with tracing * @bdev: the block device @@ -665,7 +679,7 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg) if (!q) return -ENXIO; - mutex_lock(&bdev->bd_mutex); + mutex_lock(&bdev->bd_fsfreeze_mutex); switch (cmd) { case BLKTRACESETUP: @@ -691,7 +705,7 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg) break; } - mutex_unlock(&bdev->bd_mutex); + mutex_unlock(&bdev->bd_fsfreeze_mutex); return ret; } @@ -1727,7 +1741,7 @@ static ssize_t sysfs_blk_trace_attr_show(struct device *dev, if (q == NULL) goto out_bdput; - mutex_lock(&bdev->bd_mutex); + mutex_lock(&bdev->bd_fsfreeze_mutex); if (attr == &dev_attr_enable) { ret = sprintf(buf, "%u\n", !!q->blk_trace); @@ -1746,7 +1760,7 @@ static ssize_t sysfs_blk_trace_attr_show(struct device *dev, ret = sprintf(buf, "%llu\n", q->blk_trace->end_lba); out_unlock_bdev: - mutex_unlock(&bdev->bd_mutex); + mutex_unlock(&bdev->bd_fsfreeze_mutex); out_bdput: bdput(bdev); out: @@ -1788,7 +1802,7 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev, if (q == NULL) goto out_bdput; - mutex_lock(&bdev->bd_mutex); + mutex_lock(&bdev->bd_fsfreeze_mutex); if (attr == &dev_attr_enable) { if (value) @@ -1814,7 +1828,7 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev, } out_unlock_bdev: - mutex_unlock(&bdev->bd_mutex); + mutex_unlock(&bdev->bd_fsfreeze_mutex); out_bdput: bdput(bdev); out: