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 F26C2C433F5 for ; Wed, 30 Mar 2022 05:30:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243000AbiC3FcJ (ORCPT ); Wed, 30 Mar 2022 01:32:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55578 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243005AbiC3FcF (ORCPT ); Wed, 30 Mar 2022 01:32:05 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2DE081D4195 for ; Tue, 29 Mar 2022 22:30:19 -0700 (PDT) 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=HTVHEZyGZ8zmtuIY86XJq+lNWVi5qqhfzk/kXEsV8mE=; b=YPuOnjetUNyJHEwFhMQ3BSy4J4 vNFhJtzbxPKT1RNrKyCgNR0BCX9mf6GYJGiHz9cICaz9S7d1JOtdh902HwBLCToIgSuDpfAD/0zHq Z17B8icfVl2b0Fcnk8JtisPN9sWod/JgEqTLqXUrj0LqAtjdO1p74yZ+im2iVg+uGSEdu7ASJvm+z KisP5IlJQ1IMDXCFUuVKVwacXxVMVLwUFQbQi5TzwLq+lQGhPIo/xFhq6ZDd2RwiEx9wxF37LvgLc OtLF0mhfleNjKG+uUll9qo0Kv9JvYJFSjpMcrWNFJazXFvwlhqgS2rsrmPayF4vX/c4/mbMIkGRbO El8YJz0A==; Received: from 213-225-15-62.nat.highway.a1.net ([213.225.15.62] helo=localhost) by bombadil.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nZQuL-00ELUo-Ls; Wed, 30 Mar 2022 05:30:14 +0000 From: Christoph Hellwig To: Jens Axboe , Josef Bacik , Minchan Kim , Nitin Gupta Cc: Tetsuo Handa , Jan Kara , "Darrick J . Wong" , Ming Lei , Matteo Croce , linux-block@vger.kernel.org, nbd@other.debian.org Subject: [PATCH 14/15] loop: remove lo_refcount and avoid lo_mutex in ->open / ->release Date: Wed, 30 Mar 2022 07:29:16 +0200 Message-Id: <20220330052917.2566582-15-hch@lst.de> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220330052917.2566582-1-hch@lst.de> References: <20220330052917.2566582-1-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 lo_refcount counts how many openers a loop device has, but that count is already provided by the block layer in the bd_openers field of the whole-disk block_device. Remove lo_refcount and allow opens to succeed even on devices beeing deleted - now that ->free_disk is implemented we can handle that race gracefull and all I/O on it will just fail. Similarly there is a small race window now where loop_control_remove does not synchronize the delete vs the remove due do bd_openers not being under lo_mutex protection, but we can handle that just as gracefully. Signed-off-by: Christoph Hellwig Reviewed-by: Jan Kara --- drivers/block/loop.c | 37 +++++++------------------------------ drivers/block/loop.h | 1 - 2 files changed, 7 insertions(+), 31 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index ea3b0e055657f..ca7103807d34a 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1249,7 +1249,7 @@ static int loop_clr_fd(struct loop_device *lo) * /do something like mkfs/losetup -d causing the losetup -d * command to fail with EBUSY. */ - if (atomic_read(&lo->lo_refcnt) > 1) { + if (disk_openers(lo->lo_disk) > 1) { lo->lo_flags |= LO_FLAGS_AUTOCLEAR; loop_global_unlock(lo, true); return 0; @@ -1729,33 +1729,15 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode, } #endif -static int lo_open(struct block_device *bdev, fmode_t mode) -{ - struct loop_device *lo = bdev->bd_disk->private_data; - int err; - - err = mutex_lock_killable(&lo->lo_mutex); - if (err) - return err; - if (lo->lo_state == Lo_deleting) - err = -ENXIO; - else - atomic_inc(&lo->lo_refcnt); - mutex_unlock(&lo->lo_mutex); - return err; -} - static void lo_release(struct gendisk *disk, fmode_t mode) { struct loop_device *lo = disk->private_data; - mutex_lock(&lo->lo_mutex); - if (atomic_dec_return(&lo->lo_refcnt)) - goto out_unlock; + if (disk_openers(disk) > 0) + return; - if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) { - if (lo->lo_state != Lo_bound) - goto out_unlock; + mutex_lock(&lo->lo_mutex); + if (lo->lo_state == Lo_bound && (lo->lo_flags & LO_FLAGS_AUTOCLEAR)) { lo->lo_state = Lo_rundown; mutex_unlock(&lo->lo_mutex); /* @@ -1765,8 +1747,6 @@ static void lo_release(struct gendisk *disk, fmode_t mode) __loop_clr_fd(lo, true); return; } - -out_unlock: mutex_unlock(&lo->lo_mutex); } @@ -1780,7 +1760,6 @@ static void lo_free_disk(struct gendisk *disk) static const struct block_device_operations lo_fops = { .owner = THIS_MODULE, - .open = lo_open, .release = lo_release, .ioctl = lo_ioctl, #ifdef CONFIG_COMPAT @@ -2034,7 +2013,6 @@ static int loop_add(int i) */ if (!part_shift) disk->flags |= GENHD_FL_NO_PART; - atomic_set(&lo->lo_refcnt, 0); mutex_init(&lo->lo_mutex); lo->lo_number = i; spin_lock_init(&lo->lo_lock); @@ -2124,13 +2102,12 @@ static int loop_control_remove(int idx) ret = mutex_lock_killable(&lo->lo_mutex); if (ret) goto mark_visible; - if (lo->lo_state != Lo_unbound || - atomic_read(&lo->lo_refcnt) > 0) { + if (lo->lo_state != Lo_unbound || disk_openers(lo->lo_disk) > 0) { mutex_unlock(&lo->lo_mutex); ret = -EBUSY; goto mark_visible; } - /* Mark this loop device no longer open()-able. */ + /* Mark this loop device as no more bound, but not quite unbound yet */ lo->lo_state = Lo_deleting; mutex_unlock(&lo->lo_mutex); diff --git a/drivers/block/loop.h b/drivers/block/loop.h index 082d4b6bfc6a6..449d562738c52 100644 --- a/drivers/block/loop.h +++ b/drivers/block/loop.h @@ -28,7 +28,6 @@ struct loop_func_table; struct loop_device { int lo_number; - atomic_t lo_refcnt; loff_t lo_offset; loff_t lo_sizelimit; int lo_flags; -- 2.30.2