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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C6FEFC2BA4C for ; Wed, 26 Jan 2022 15:51:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236019AbiAZPvI (ORCPT ); Wed, 26 Jan 2022 10:51:08 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50178 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236114AbiAZPvH (ORCPT ); Wed, 26 Jan 2022 10:51:07 -0500 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8FB44C06173B for ; Wed, 26 Jan 2022 07:51:07 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From:Sender :Reply-To:Content-Type:Content-ID:Content-Description; bh=+z9BCWEVZR0qmxdIpRWZf3RBB6NlkLhMsrLB//YKZJ8=; b=ZPVbwlcsRpmQ+9O4wf9y2gyioc wtkWXN0kE654ovurEbZ33SI8kF63Sq7FTe4Ik9dknh2xyrX08mhZIt+UGiXG8tBhzxhl06ZDUAcnd 739QnRZt/PVMPbcABlc2X/AjZnW+vFs14+MTRQnei1He5mH+WHTwW006FRVBiaQk/xTi2Y8LvLAGz uOKetgUS136dvnoI2e/RloE7JJchWMjBGOvMgznWdy506fRaAb6BWsFEzdWoWUZq5cFDitVE+8oQm kyj7EkW1cltr+5mlSibPQC+mH/7/Iz8irwSv6/+1MkK+8BI6t/FXp5lNT+gOJIUyHfB4nQH+JYO7E wZ6/ba2g==; Received: from [2001:4bb8:180:4c4c:c422:bb0a:5a5f:dce0] (helo=localhost) by bombadil.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nCkZc-00CQEF-Mi; Wed, 26 Jan 2022 15:51:05 +0000 From: Christoph Hellwig To: Jens Axboe Cc: Tetsuo Handa , Jan Kara , linux-block@vger.kernel.org, Ming Lei , Tetsuo Handa , kernel test robot , syzbot Subject: [PATCH 8/8] loop: make autoclear operation synchronous again Date: Wed, 26 Jan 2022 16:50:40 +0100 Message-Id: <20220126155040.1190842-9-hch@lst.de> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220126155040.1190842-1-hch@lst.de> References: <20220126155040.1190842-1-hch@lst.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org From: Tetsuo Handa The kernel test robot is reporting that xfstest can fail at umount ext2 on xfs umount xfs sequence, for commit 322c4293ecc58110 ("loop: make autoclear operation asynchronous") broke what commit ("loop: Make explicit loop device destruction lazy") wanted to achieve. Although we cannot guarantee that nobody is holding a reference when "umount xfs" is called, we should try to close a race window opened by asynchronous autoclear operation. It turned out that there is no need to call flush_workqueue() from __loop_clr_fd(), for blk_mq_freeze_queue() blocks until all pending "struct work_struct" are processed by loop_process_work(). Revert commit 322c4293ecc58110 ("loop: make autoclear operation asynchronous"), and simply defer calling destroy_workqueue() till loop_remove() after ensuring that the worker rbtree and repaing timer are kept alive while the loop device exists. Since a loop device is likely reused after once created thanks to ioctl(LOOP_CTL_GET_FREE), being unable to destroy corresponding WQ when ioctl(LOOP_CLR_FD) is called should be an acceptable waste. Reported-by: kernel test robot Suggested-by: Christoph Hellwig Tested-by: syzbot Signed-off-by: Tetsuo Handa [hch: rebased, keep the work rbtree and timer around longer] Signed-off-by: Christoph Hellwig --- drivers/block/loop.c | 71 ++++++++++++++------------------------------ drivers/block/loop.h | 1 - 2 files changed, 23 insertions(+), 49 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index fc0cdd1612b1d..cf7830a68113a 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1038,10 +1038,10 @@ static int loop_configure(struct loop_device *lo, fmode_t mode, !file->f_op->write_iter) lo->lo_flags |= LO_FLAGS_READ_ONLY; - lo->workqueue = alloc_workqueue("loop%d", - WQ_UNBOUND | WQ_FREEZABLE, - 0, - lo->lo_number); + if (!lo->workqueue) + lo->workqueue = alloc_workqueue("loop%d", + WQ_UNBOUND | WQ_FREEZABLE, + 0, lo->lo_number); if (!lo->workqueue) { error = -ENOMEM; goto out_unlock; @@ -1147,10 +1147,6 @@ static void __loop_clr_fd(struct loop_device *lo, bool release) if (!release) blk_mq_freeze_queue(lo->lo_queue); - destroy_workqueue(lo->workqueue); - loop_free_idle_workers(lo, true); - del_timer_sync(&lo->timer); - spin_lock_irq(&lo->lo_lock); filp = lo->lo_backing_file; lo->lo_backing_file = NULL; @@ -1176,9 +1172,11 @@ static void __loop_clr_fd(struct loop_device *lo, bool release) if (lo->lo_flags & LO_FLAGS_PARTSCAN) { int err; - mutex_lock(&lo->lo_disk->open_mutex); + if (!release) + mutex_lock(&lo->lo_disk->open_mutex); err = bdev_disk_changed(lo->lo_disk, false); - mutex_unlock(&lo->lo_disk->open_mutex); + if (!release) + mutex_unlock(&lo->lo_disk->open_mutex); if (err) pr_warn("%s: partition scan of loop%d failed (rc=%d)\n", __func__, lo->lo_number, err); @@ -1189,39 +1187,17 @@ static void __loop_clr_fd(struct loop_device *lo, bool release) if (!part_shift) lo->lo_disk->flags |= GENHD_FL_NO_PART; - fput(filp); -} - -static void loop_rundown_completed(struct loop_device *lo) -{ mutex_lock(&lo->lo_mutex); lo->lo_state = Lo_unbound; mutex_unlock(&lo->lo_mutex); module_put(THIS_MODULE); -} - -static void loop_rundown_workfn(struct work_struct *work) -{ - struct loop_device *lo = container_of(work, struct loop_device, - rundown_work); - struct block_device *bdev = lo->lo_device; - struct gendisk *disk = lo->lo_disk; - __loop_clr_fd(lo, true); - kobject_put(&bdev->bd_device.kobj); - module_put(disk->fops->owner); - loop_rundown_completed(lo); -} - -static void loop_schedule_rundown(struct loop_device *lo) -{ - struct block_device *bdev = lo->lo_device; - struct gendisk *disk = lo->lo_disk; - - __module_get(disk->fops->owner); - kobject_get(&bdev->bd_device.kobj); - INIT_WORK(&lo->rundown_work, loop_rundown_workfn); - queue_work(system_long_wq, &lo->rundown_work); + /* + * Need not hold lo_mutex to fput backing file. Calling fput holding + * lo_mutex triggers a circular lock dependency possibility warning as + * fput can take open_mutex which is usually taken before lo_mutex. + */ + fput(filp); } static int loop_clr_fd(struct loop_device *lo) @@ -1254,7 +1230,6 @@ static int loop_clr_fd(struct loop_device *lo) mutex_unlock(&lo->lo_mutex); __loop_clr_fd(lo, false); - loop_rundown_completed(lo); return 0; } @@ -1753,20 +1728,14 @@ static void lo_release(struct gendisk *disk, fmode_t mode) return; mutex_lock(&lo->lo_mutex); - if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) { - if (lo->lo_state != Lo_bound) - goto out_unlock; + if (lo->lo_state == Lo_bound && + (lo->lo_flags & LO_FLAGS_AUTOCLEAR)) { lo->lo_state = Lo_rundown; mutex_unlock(&lo->lo_mutex); - /* - * In autoclear mode, stop the loop thread - * and remove configuration after last close. - */ - loop_schedule_rundown(lo); + __loop_clr_fd(lo, true); return; } -out_unlock: mutex_unlock(&lo->lo_mutex); } @@ -2056,6 +2025,12 @@ static void loop_remove(struct loop_device *lo) mutex_lock(&loop_ctl_mutex); idr_remove(&loop_index_idr, lo->lo_number); mutex_unlock(&loop_ctl_mutex); + + if (lo->workqueue) + destroy_workqueue(lo->workqueue); + loop_free_idle_workers(lo, true); + del_timer_sync(&lo->timer); + /* There is no route which can find this loop device. */ mutex_destroy(&lo->lo_mutex); kfree(lo); diff --git a/drivers/block/loop.h b/drivers/block/loop.h index 918a7a2dc0259..082d4b6bfc6a6 100644 --- a/drivers/block/loop.h +++ b/drivers/block/loop.h @@ -56,7 +56,6 @@ struct loop_device { struct gendisk *lo_disk; struct mutex lo_mutex; bool idr_visible; - struct work_struct rundown_work; }; struct loop_cmd { -- 2.30.2