From patchwork Fri Feb 9 18:44:05 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Bart Van Assche X-Patchwork-Id: 10209803 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 D24C260245 for ; Fri, 9 Feb 2018 18:44:10 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C1DE029825 for ; Fri, 9 Feb 2018 18:44:10 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B685D29862; Fri, 9 Feb 2018 18:44:10 +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=-6.8 required=2.0 tests=BAYES_00,DKIM_SIGNED, RCVD_IN_DNSWL_HI,T_DKIM_INVALID 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 2F01029825 for ; Fri, 9 Feb 2018 18:44:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752192AbeBISoJ (ORCPT ); Fri, 9 Feb 2018 13:44:09 -0500 Received: from esa1.hgst.iphmx.com ([68.232.141.245]:53758 "EHLO esa1.hgst.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752386AbeBISoH (ORCPT ); Fri, 9 Feb 2018 13:44:07 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=wdc.com; i=@wdc.com; q=dns/txt; s=dkim.wdc.com; t=1518201847; x=1549737847; h=from:to:cc:subject:date:message-id:in-reply-to: references; bh=ibchXgpenFHNT+TWRkLVd1mHmLPGgUDWz0nsT53hoCk=; b=rDui1wulYFvjdRb3siE2KyHvUhk7M5zYUWVft7RAUrurY+zG/IY99b5e X05YZnDGxICEqFC1gJ/cSmCvFhe0TXgVanM1TK4Sojoppi/4gF02LzIqf c/r98f9sIiAV0cAKOeMhyPMbTeZfZ8sB3aYXi1+Ui7cyDZvfKCWBRV5Nf ZyhWf8Pp29NW1vwSIK7fXzXGUmbuu46ydCbC1MGgZSzAfYHb3qu8FWvxC KnSpTW1gwCNWpskDY4TOpLEy38Xll+xso2Koo6Mky/7awn3T2qZbY0GC3 TX5WLGqIKhomh1WedxjEGi0ZM9vDgnOxMOBZKWT91xf1cf0B91Ir964c5 g==; X-IronPort-AV: E=Sophos;i="5.46,483,1511798400"; d="scan'208";a="174009670" Received: from h199-255-45-15.hgst.com (HELO uls-op-cesaep02.wdc.com) ([199.255.45.15]) by ob1.hgst.iphmx.com with ESMTP; 10 Feb 2018 02:44:06 +0800 Received: from uls-op-cesaip02.wdc.com ([10.248.3.37]) by uls-op-cesaep02.wdc.com with ESMTP; 09 Feb 2018 10:38:23 -0800 Received: from thinkpad-bart.sdcorp.global.sandisk.com (HELO thinkpad-bart.int.fusionio.com) ([10.11.171.236]) by uls-op-cesaip02.wdc.com with ESMTP; 09 Feb 2018 10:44:07 -0800 From: Bart Van Assche To: Jens Axboe Cc: linux-block@vger.kernel.org, Christoph Hellwig , Jan Kara , Joseph Qi , Bart Van Assche Subject: [PATCH v3 3/3] block: Fix a race between request queue removal and the block cgroup controller Date: Fri, 9 Feb 2018 10:44:05 -0800 Message-Id: <20180209184405.25835-4-bart.vanassche@wdc.com> X-Mailer: git-send-email 2.16.1 In-Reply-To: <20180209184405.25835-1-bart.vanassche@wdc.com> References: <20180209184405.25835-1-bart.vanassche@wdc.com> 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 Avoid that the following race can occur: blk_cleanup_queue() blkcg_print_blkgs() spin_lock_irq(lock) (1) spin_lock_irq(blkg->q->queue_lock) (2,5) q->queue_lock = &q->__queue_lock (3) spin_unlock_irq(lock) (4) spin_unlock_irq(blkg->q->queue_lock) (6) (1) take driver lock; (2) busy loop for driver lock; (3) override driver lock with internal lock; (4) unlock driver lock; (5) can take driver lock now; (6) but unlock internal lock. This change is safe because only the SCSI core and the NVME core keep a reference on a request queue after having called blk_cleanup_queue(). Neither driver accesses any of the removed data structures between its blk_cleanup_queue() and blk_put_queue() calls. Reported-by: Joseph Qi Signed-off-by: Bart Van Assche Cc: Jan Kara --- block/blk-core.c | 31 +++++++++++++++++++++++++++++++ block/blk-sysfs.c | 7 ------- 2 files changed, 31 insertions(+), 7 deletions(-) diff --git a/block/blk-core.c b/block/blk-core.c index 41c74b37be85..6febc69a58aa 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -719,6 +719,37 @@ void blk_cleanup_queue(struct request_queue *q) del_timer_sync(&q->backing_dev_info->laptop_mode_wb_timer); blk_sync_queue(q); + /* + * I/O scheduler exit is only safe after the sysfs scheduler attribute + * has been removed. + */ + WARN_ON_ONCE(q->kobj.state_in_sysfs); + + /* + * Since the I/O scheduler exit code may access cgroup information, + * perform I/O scheduler exit before disassociating from the block + * cgroup controller. + */ + if (q->elevator) { + ioc_clear_queue(q); + elevator_exit(q, q->elevator); + q->elevator = NULL; + } + + /* + * Remove all references to @q from the block cgroup controller before + * restoring @q->queue_lock to avoid that restoring this pointer causes + * e.g. blkcg_print_blkgs() to crash. + */ + blkcg_exit_queue(q); + + /* + * Since the cgroup code may dereference the @q->backing_dev_info + * pointer, only decrease its reference count after having removed the + * association with the block cgroup controller. + */ + bdi_put(q->backing_dev_info); + if (q->mq_ops) blk_mq_free_queue(q); percpu_ref_exit(&q->q_usage_counter); diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index cbea895a5547..fd71a00c9462 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -798,13 +798,6 @@ static void __blk_release_queue(struct work_struct *work) if (test_bit(QUEUE_FLAG_POLL_STATS, &q->queue_flags)) blk_stat_remove_callback(q, q->poll_cb); blk_stat_free_callback(q->poll_cb); - bdi_put(q->backing_dev_info); - blkcg_exit_queue(q); - - if (q->elevator) { - ioc_clear_queue(q); - elevator_exit(q, q->elevator); - } blk_free_queue_stats(q->stats);