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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 BEA9AC433E1 for ; Mon, 18 May 2020 17:39:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 95CAC2086A for ; Mon, 18 May 2020 17:39:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589823541; bh=TEoHXFMTbejUrHlaEUHwHNavdgX9+aD2ECPMfE4eKks=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=gEoFvUU9w8jcoZYeI7qVCp8I0IdVC8kX4zsDtn8i+fHyHKvCFp43S7AZPluKGBtUT i+v81echN9ARq1w/mBaBDFZBfwk2IMkVSw/br+EF/6Z9eq7BkSL85DxrSvl4ZDpWrX +k8xzIxYd76n8C39LavWxUsBHtMGOCD2VHi6vYy0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728677AbgERRjA (ORCPT ); Mon, 18 May 2020 13:39:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:33342 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728657AbgERRi7 (ORCPT ); Mon, 18 May 2020 13:38:59 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 02265207C4; Mon, 18 May 2020 17:38:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589823538; bh=TEoHXFMTbejUrHlaEUHwHNavdgX9+aD2ECPMfE4eKks=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DDS0WHmuYvQIslNGO/h5SYpH7o7Xg4tkQhA3XnqRTB8CTckZnJEC3kVqDx5oEdpvz 55AbYmbS0Bilsc1wk22yj2Nljkemvls80tu+zekR7ydMpXdQO/eNVbm2reOiuBZlFN cCmJJ04U+eGP3B39O4+fReDSLZ/lHfQc+RbR/4dw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Christoph Hellwig , Waiman Long , "Steven Rostedt (VMware)" , Jens Axboe , Ben Hutchings Subject: [PATCH 4.4 23/86] blktrace: Fix potential deadlock between delete & sysfs ops Date: Mon, 18 May 2020 19:35:54 +0200 Message-Id: <20200518173455.161566394@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200518173450.254571947@linuxfoundation.org> References: <20200518173450.254571947@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Waiman Long commit 5acb3cc2c2e9d3020a4fee43763c6463767f1572 upstream. 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, a new blk_trace_mutex is now added to the request_queue structure to protect access to the blk_trace structure. Suggested-by: Christoph Hellwig Signed-off-by: Waiman Long Acked-by: Steven Rostedt (VMware) Fix typo in patch subject line, and prune a comment detailing how the code used to work. Signed-off-by: Jens Axboe Signed-off-by: Ben Hutchings Signed-off-by: Greg Kroah-Hartman --- block/blk-core.c | 3 +++ include/linux/blkdev.h | 1 + kernel/trace/blktrace.c | 18 ++++++++++++------ 3 files changed, 16 insertions(+), 6 deletions(-) --- a/block/blk-core.c +++ b/block/blk-core.c @@ -719,6 +719,9 @@ struct request_queue *blk_alloc_queue_no kobject_init(&q->kobj, &blk_queue_ktype); +#ifdef CONFIG_BLK_DEV_IO_TRACE + mutex_init(&q->blk_trace_mutex); +#endif mutex_init(&q->sysfs_lock); spin_lock_init(&q->__queue_lock); --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -432,6 +432,7 @@ struct request_queue { int node; #ifdef CONFIG_BLK_DEV_IO_TRACE struct blk_trace *blk_trace; + struct mutex blk_trace_mutex; #endif /* * for flush operations --- a/kernel/trace/blktrace.c +++ b/kernel/trace/blktrace.c @@ -644,6 +644,12 @@ int blk_trace_startstop(struct request_q } 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. + */ + /** * blk_trace_ioctl: - handle the ioctls associated with tracing * @bdev: the block device @@ -661,7 +667,7 @@ int blk_trace_ioctl(struct block_device if (!q) return -ENXIO; - mutex_lock(&bdev->bd_mutex); + mutex_lock(&q->blk_trace_mutex); switch (cmd) { case BLKTRACESETUP: @@ -687,7 +693,7 @@ int blk_trace_ioctl(struct block_device break; } - mutex_unlock(&bdev->bd_mutex); + mutex_unlock(&q->blk_trace_mutex); return ret; } @@ -1652,7 +1658,7 @@ static ssize_t sysfs_blk_trace_attr_show if (q == NULL) goto out_bdput; - mutex_lock(&bdev->bd_mutex); + mutex_lock(&q->blk_trace_mutex); if (attr == &dev_attr_enable) { ret = sprintf(buf, "%u\n", !!q->blk_trace); @@ -1671,7 +1677,7 @@ static ssize_t sysfs_blk_trace_attr_show ret = sprintf(buf, "%llu\n", q->blk_trace->end_lba); out_unlock_bdev: - mutex_unlock(&bdev->bd_mutex); + mutex_unlock(&q->blk_trace_mutex); out_bdput: bdput(bdev); out: @@ -1713,7 +1719,7 @@ static ssize_t sysfs_blk_trace_attr_stor if (q == NULL) goto out_bdput; - mutex_lock(&bdev->bd_mutex); + mutex_lock(&q->blk_trace_mutex); if (attr == &dev_attr_enable) { if (!!value == !!q->blk_trace) { @@ -1743,7 +1749,7 @@ static ssize_t sysfs_blk_trace_attr_stor } out_unlock_bdev: - mutex_unlock(&bdev->bd_mutex); + mutex_unlock(&q->blk_trace_mutex); out_bdput: bdput(bdev); out: