From patchwork Fri Feb 11 07:15:54 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tetsuo Handa X-Patchwork-Id: 12742951 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 626D4C4332F for ; Fri, 11 Feb 2022 07:16:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234505AbiBKHQ1 (ORCPT ); Fri, 11 Feb 2022 02:16:27 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:38400 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241343AbiBKHQ0 (ORCPT ); Fri, 11 Feb 2022 02:16:26 -0500 Received: from www262.sakura.ne.jp (www262.sakura.ne.jp [202.181.97.72]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 86F0D113A for ; Thu, 10 Feb 2022 23:16:24 -0800 (PST) Received: from fsav311.sakura.ne.jp (fsav311.sakura.ne.jp [153.120.85.142]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 21B7G0nE012326; Fri, 11 Feb 2022 16:16:01 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav311.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav311.sakura.ne.jp); Fri, 11 Feb 2022 16:16:00 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav311.sakura.ne.jp) Received: from localhost.localdomain (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 21B7Fuia011955 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Fri, 11 Feb 2022 16:16:00 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) From: Tetsuo Handa To: Jens Axboe Cc: linux-block , Tetsuo Handa , Christoph Hellwig , Jan Kara , kernel test robot Subject: [PATCH for 5.17] loop: revert "make autoclear operation asynchronous" Date: Fri, 11 Feb 2022 16:15:54 +0900 Message-Id: <20220211071554.3424-1-penguin-kernel@I-love.SAKURA.ne.jp> X-Mailer: git-send-email 2.18.4 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org The kernel test robot is reporting that xfstest which does umount ext2 on xfs umount xfs sequence started failing, for commit 322c4293ecc58110 ("loop: make autoclear operation asynchronous") removed a guarantee that fput() of backing file is processed before lo_release() from close() returns to user mode. And syzbot is reporting that deferring destroy_workqueue() from __loop_clr_fd() to a WQ context did not help [1]. Revert that commit. Link: https://syzkaller.appspot.com/bug?extid=831661966588c802aae9 [1] Reported-by: kernel test robot Acked-by: Jan Kara Reviewed-by: Christoph Hellwig Reported-by: syzbot Signed-off-by: Tetsuo Handa --- drivers/block/loop.c | 65 ++++++++++++++++++++------------------------ drivers/block/loop.h | 1 - 2 files changed, 29 insertions(+), 37 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 01cbbfc4e9e2..150012ffb387 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1082,7 +1082,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode, return error; } -static void __loop_clr_fd(struct loop_device *lo) +static void __loop_clr_fd(struct loop_device *lo, bool release) { struct file *filp; gfp_t gfp = lo->old_gfp_mask; @@ -1144,6 +1144,8 @@ static void __loop_clr_fd(struct loop_device *lo) /* let user-space know about this change */ kobject_uevent(&disk_to_dev(lo->lo_disk)->kobj, KOBJ_CHANGE); mapping_set_gfp_mask(filp->f_mapping, gfp); + /* This is safe: open() is still holding a reference. */ + module_put(THIS_MODULE); blk_mq_unfreeze_queue(lo->lo_queue); disk_force_media_change(lo->lo_disk, DISK_EVENT_MEDIA_CHANGE); @@ -1151,52 +1153,44 @@ static void __loop_clr_fd(struct loop_device *lo) if (lo->lo_flags & LO_FLAGS_PARTSCAN) { int err; - mutex_lock(&lo->lo_disk->open_mutex); + /* + * open_mutex has been held already in release path, so don't + * acquire it if this function is called in such case. + * + * If the reread partition isn't from release path, lo_refcnt + * must be at least one and it can only become zero when the + * current holder is released. + */ + 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); /* Device is gone, no point in returning error */ } + /* + * lo->lo_state is set to Lo_unbound here after above partscan has + * finished. There cannot be anybody else entering __loop_clr_fd() as + * Lo_rundown state protects us from all the other places trying to + * change the 'lo' device. + */ lo->lo_flags = 0; 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); - 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) @@ -1228,8 +1222,7 @@ static int loop_clr_fd(struct loop_device *lo) lo->lo_state = Lo_rundown; mutex_unlock(&lo->lo_mutex); - __loop_clr_fd(lo); - loop_rundown_completed(lo); + __loop_clr_fd(lo, false); return 0; } @@ -1754,7 +1747,7 @@ static void lo_release(struct gendisk *disk, fmode_t mode) * In autoclear mode, stop the loop thread * and remove configuration after last close. */ - loop_schedule_rundown(lo); + __loop_clr_fd(lo, true); return; } else if (lo->lo_state == Lo_bound) { /* diff --git a/drivers/block/loop.h b/drivers/block/loop.h index 918a7a2dc025..082d4b6bfc6a 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 {