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 0993FC433F5 for ; Fri, 28 Jan 2022 13:00:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237628AbiA1NAj (ORCPT ); Fri, 28 Jan 2022 08:00:39 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50744 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237744AbiA1NAj (ORCPT ); Fri, 28 Jan 2022 08:00:39 -0500 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EA9C4C061714 for ; Fri, 28 Jan 2022 05:00:38 -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=40Ln9gDPp3kPkgkvhK8rKN7ZrGwDo8dGmxn1bbHSx0c=; b=MiF2eG7i5lXZxTX3xWB3Hp3gdf K8S/W48IzL9fVdtTnFElYu9t6nis/QQmG3ZudqJj6F0bNArBu9N3poA9/iZ+7DaexlRL/2DyfTf5y ZT4MK40kDD5rcmHzSx6Zj+vkcvtLR9t9OvJ8uvMWJGvPZ45ClY4D4tdE7LX/iUGJrCml2syfxbohm EB7dSp549MUQtte+W7POaudCIxHu3HJP1L4NS4FjTVOUgAhz+FfVhKqshVEYLcz8Uy3hZH0UchLy0 TY0cNFYY1fV/Ab5WQ86YWUQU3T9gfiWukTW4BxpqcjAHLuT8EIh17K3Oqb+79eELs+AmPB23O58rm qisgOIlg==; Received: from [2001:4bb8:180:4c4c:73e:e8c7:4199:32d7] (helo=localhost) by bombadil.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nDQrj-0028vY-Qr; Fri, 28 Jan 2022 13:00:36 +0000 From: Christoph Hellwig To: Jens Axboe Cc: Tetsuo Handa , Jan Kara , linux-block@vger.kernel.org, Ming Lei , "Darrick J . Wong" Subject: [PATCH 4/8] loop: only take lo_mutex for the last reference in lo_release Date: Fri, 28 Jan 2022 14:00:18 +0100 Message-Id: <20220128130022.1750906-5-hch@lst.de> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220128130022.1750906-1-hch@lst.de> References: <20220128130022.1750906-1-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_refcnt is only incremented in lo_open and decremented in lo_release, and thus protected by open_mutex. Only take lo_mutex when lo_release actually takes action for the final release. Signed-off-by: Christoph Hellwig Tested-by: Darrick J. Wong --- drivers/block/loop.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index d3a7f281ce1b6..b58dc95f80d96 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1740,10 +1740,14 @@ 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; + /* + * Note: this requires disk->open_mutex to protect against races + * with lo_open. + */ + if (!atomic_dec_and_test(&lo->lo_refcnt)) + return; + mutex_lock(&lo->lo_mutex); if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) { if (lo->lo_state != Lo_bound) goto out_unlock; -- 2.30.2