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 BBD78C001DE for ; Wed, 9 Aug 2023 22:39:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232989AbjHIWj0 (ORCPT ); Wed, 9 Aug 2023 18:39:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46000 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232953AbjHIWjZ (ORCPT ); Wed, 9 Aug 2023 18:39:25 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 92C55D2; Wed, 9 Aug 2023 15:39:24 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 3080364B98; Wed, 9 Aug 2023 22:39:24 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8C7C7C433C7; Wed, 9 Aug 2023 22:39:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1691620763; bh=CLgp0tXW3whDoLzghtguOCNYI43fpGW6om+fUAlt814=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Wne7raqRTdWHu6mipSTlfZt/A5MQaxdCrkanOu7ANiFhyHyQkLuaGOLCKVoLY0Ns/ vW7ZMOInmdN3+tgqvqPwGeXevfmE/aSOYNjH2bYVLFl1ryoYPPshT8AXUTx2sw5DDx P1TZOQPm/QoktPNMsc7G1in4S3wsN/b1NZ+UMOyWDXX5Ct0wkxALJfo1kJZXWItRu4 FnUYb08nA42np4hxi9KaA9A6+vNL8Dcx9FbTt6E/Buk0jf4z4hzMcajKzid6MaTbaB QBwPYEd9Hbvbfwl3JUTs/cUGYes8/WoMmWE05RxKSJ/tT1EHcFAkKJ4de+Pt3WCBUR uxdkZwXvQ8Cdg== Date: Wed, 9 Aug 2023 15:39:23 -0700 From: "Darrick J. Wong" To: Christoph Hellwig Cc: Al Viro , Christian Brauner , Namjae Jeon , Sungjong Seo , Theodore Ts'o , Andreas Dilger , Konstantin Komarov , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, ntfs3@lists.linux.dev, linux-xfs@vger.kernel.org Subject: Re: [PATCH 07/13] xfs: document the invalidate_bdev call in invalidate_bdev Message-ID: <20230809223923.GX11352@frogsfrogsfrogs> References: <20230809220545.1308228-1-hch@lst.de> <20230809220545.1308228-8-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230809220545.1308228-8-hch@lst.de> Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Wed, Aug 09, 2023 at 03:05:39PM -0700, Christoph Hellwig wrote: > Copy and paste the commit message from Darrick into a comment to explain > the seemly odd invalidate_bdev in xfs_shutdown_devices. ^ seemingly? > > Signed-off-by: Christoph Hellwig > --- > fs/xfs/xfs_super.c | 26 ++++++++++++++++++++++++++ > 1 file changed, 26 insertions(+) > > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c > index 4ae3b01ed038c7..c169beb0d8cab3 100644 > --- a/fs/xfs/xfs_super.c > +++ b/fs/xfs/xfs_super.c > @@ -399,6 +399,32 @@ STATIC void > xfs_shutdown_devices( > struct xfs_mount *mp) > { > + /* > + * Udev is triggered whenever anyone closes a block device or unmounts > + * a file systemm on a block device. > + * The default udev rules invoke blkid to read the fs super and create > + * symlinks to the bdev under /dev/disk. For this, it uses buffered > + * reads through the page cache. > + * > + * xfs_db also uses buffered reads to examine metadata. There is no > + * coordination between xfs_db and udev, which means that they can run > + * concurrently. Note there is no coordination between the kernel and > + * blkid either. > + * > + * On a system with 64k pages, the page cache can cache the superblock > + * and the root inode (and hence the root directory) with the same 64k > + * page. If udev spawns blkid after the mkfs and the system is busy > + * enough that it is still running when xfs_db starts up, they'll both > + * read from the same page in the pagecache. > + * > + * The unmount writes updated inode metadata to disk directly. The XFS > + * buffer cache does not use the bdev pagecache, nor does it invalidate > + * the pagecache on umount. If the above scenario occurs, the pagecache This sentence reads a little strangely, since "nor does it invalidate" would seem to conflict with the invalidate_bdev call below. I suggest changing the verb a bit: "The XFS buffer cache does not use the bdev pagecache, so it needs to invalidate that pagecache on unmount." With those two things changed, Reviewed-by: Darrick J. Wong --D > + * no longer reflects what's on disk, xfs_db reads the stale metadata, > + * and fails to find /a. Most of the time this succeeds because closing > + * a bdev invalidates the page cache, but when processes race, everyone > + * loses. > + */ > if (mp->m_logdev_targp && mp->m_logdev_targp != mp->m_ddev_targp) { > blkdev_issue_flush(mp->m_logdev_targp->bt_bdev); > invalidate_bdev(mp->m_logdev_targp->bt_bdev); > -- > 2.39.2 >