Path: news.gmane.org!not-for-mail

From: Niels de Vos <ndevos@redhat.com>

Newsgroups: gmane.linux.kernel,gmane.linux.file-systems

Subject: [PATCH v2] fs: Invalidate the cache for a parent block-device if fsync() is called for a partition

Date: Mon, 23 Jan 2012 10:38:29 +0000

Lines: 58

Approved: news@gmane.org

Message-ID: <1327315109-7740-1-git-send-email-ndevos@redhat.com>

References: <4F19356E.3020708@redhat.com>

NNTP-Posting-Host: lo.gmane.org

X-Trace: dough.gmane.org 1327315263 30652 80.91.229.12 (23 Jan 2012 10:41:03 GMT)

X-Complaints-To: usenet@dough.gmane.org

NNTP-Posting-Date: Mon, 23 Jan 2012 10:41:03 +0000 (UTC)

Cc: linux-kernel@vger.kernel.org, Niels de Vos <ndevos@redhat.com>,

	"Bryn M. Reeves" <bmr@redhat.com>,

	Mikulas Patocka <mpatocka@redhat.com>

To: linux-fsdevel@vger.kernel.org

Original-X-From: linux-kernel-owner@vger.kernel.org Mon Jan 23 11:40:58 2012

Return-path: <linux-kernel-owner@vger.kernel.org>

Envelope-to: glk-linux-kernel-3@lo.gmane.org

Original-Received: from vger.kernel.org ([209.132.180.67])

	by lo.gmane.org with esmtp (Exim 4.69)

	(envelope-from <linux-kernel-owner@vger.kernel.org>)

	id 1RpHKb-0008Bu-Fh

	for glk-linux-kernel-3@lo.gmane.org; Mon, 23 Jan 2012 11:40:57 +0100

Original-Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand

	id S1753263Ab2AWKkt (ORCPT <rfc822;glk-linux-kernel-3@m.gmane.org>);

	Mon, 23 Jan 2012 05:40:49 -0500

Original-Received: from mx1.redhat.com ([209.132.183.28]:58739 "EHLO mx1.redhat.com"

	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP

	id S1751990Ab2AWKks (ORCPT <rfc822;linux-kernel@vger.kernel.org>);

	Mon, 23 Jan 2012 05:40:48 -0500

Original-Received: from int-mx12.intmail.prod.int.phx2.redhat.com (int-mx12.intmail.prod.int.phx2.redhat.com [10.5.11.25])

	by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q0NAelMx027033

	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK);

	Mon, 23 Jan 2012 05:40:47 -0500

Original-Received: from ndevos.usersys.redhat.com (dhcp-1-51.fab.redhat.com [10.33.1.51])

	by int-mx12.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id q0NAejLn013691;

	Mon, 23 Jan 2012 05:40:46 -0500

In-Reply-To: <4F19356E.3020708@redhat.com>

X-Scanned-By: MIMEDefang 2.68 on 10.5.11.25

Original-Sender: linux-kernel-owner@vger.kernel.org

Precedence: bulk

List-ID: <linux-kernel.vger.kernel.org>

X-Mailing-List: linux-kernel@vger.kernel.org

Xref: news.gmane.org gmane.linux.kernel:1242432 gmane.linux.file-systems:60751

Archived-At: <http://permalink.gmane.org/gmane.linux.kernel/1242432>

Executing an fsync() on a file-descriptor of a partition flushes the

caches for that partition by calling blkdev_issue_flush(). However, it

seems that reading data through the parent device will still return the

old cached data.

The cache for the block-device is not synced if the block-device is kept

open (due to a mounted partition, for example). Only when all users for

the disk have exited, the cache for the disk is made consistent again.

Calling invalidate_bdev() on the parent block-device in case

blkdev_fsync() was called for a partition, fixes this.

The problem can be worked around by forcing the caches to be flushed

with either

	# blockdev --flushbufs ${dev_disk}

or

	# echo 3 > /proc/sys/vm/drop_caches

CC: Bryn M. Reeves <bmr@redhat.com>

CC: Mikulas Patocka <mpatocka@redhat.com>

Signed-off-by: Niels de Vos <ndevos@redhat.com>

---

v2:

- Do not call invalidate_bdev() from blkdev_issue_flush() and prevent

  performance degration with journalled filesystems.

  Suggested was to call invalidate_bdev() in fsync_bdev(), but this is

  not in the call-path of mkfs.ext3 and similar tools. Hence the issue

  persists.

- Correct phrasing a little, changing ioctl-BLKFLSBUF is not required.

- This issue also occurs when doing an ioctl-BLKFLSBUF on a partition.

  Reading the whole disk will still return cached data. If this is an

  issue, it will need a seperate patch.

---

 fs/block_dev.c |    4 ++++

 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c

index 0e575d1..433c4de 100644

--- a/fs/block_dev.c

+++ b/fs/block_dev.c

@@ -424,6 +424,10 @@ int blkdev_fsync(struct file *filp, loff_t start, loff_t end, int datasync)

 	if (error == -EOPNOTSUPP)

 		error = 0;

+	/* invalidate parent block_device */

+	if (!error && bdev != bdev->bd_contains)

+		invalidate_bdev(bdev->bd_contains);

+

 	return error;

 }

 EXPORT_SYMBOL(blkdev_fsync);

-- 

1.7.6.5