[ 3.5.y.z extended stable ] Patch "fs/block_dev.c: page cache wrongly left invalidated after" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    fs/block_dev.c: page cache wrongly left invalidated after

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From a36a9d88b442afb59bf13f4e086d855f48b77d37 Mon Sep 17 00:00:00 2001
From: MITSUNARI Shigeo <herumi at nifty.com>
Date: Thu, 21 Feb 2013 16:42:01 -0800
Subject: [PATCH] fs/block_dev.c: page cache wrongly left invalidated after
 revalidate_disk()

commit 7630b661da330b35dd57b6f5d6d62b386f2dd751 upstream.

We found that bdev->bd_invalidated was left set once revalidate_disk()
is called, which results in page cache flush every time that device is
open.

Specifically, we found this problem in MD block device.  Once we resize
a MD device, mdadm --monitor periodically flush all page cache for that
device every 60 or 1000 seconds when it opens the device.

This bug lies since at least 3.2.0 till the latest kernel(3.6.2).  Patch
is attached.

The following steps will reproduce the problem.

1. prepair a block device (eg /dev/sdb).

2. create two partitions:

   sudo parted /dev/sdb
   mklabel gpt
   mkpart primary 0% 50%
   mkpart primary 50% 100%

3. create a md device.

   sudo mdadm -C /dev/md/hoge -l 1 -n 2 -e 1.2 --assume-clean --auto=md --symlink=no /dev/sdb1 /dev/sdb2

4. create file system and mount it

   sudo mkfs.ext3 /dev/md/hoge
   sudo mkdir /mnt/test
   sudo mount /dev/md/hoge /mnt/test

5. try to resize the device

   sudo mdadm -G /dev/md/hoge --size=max

6. create a file to fill file cache.

  sudo dd if=/dev/urandom of=/mnt/test/data bs=1M count=10

and verify the current status of file by free command.

7. mdadm monitor will open the md device every 1000 seconds and you
   will find all file cache on the device are cleared.

The timing can be reduced by the following steps.

a) kill mdadm and restart it with --delay option

   /sbin/mdadm --monitor --delay=30 --pid-file /var/run/mdadm/monitor.pid --daemonise --scan --syslog

or open the md device directly.

   sudo dd if=/dev/md/hoge of=/dev/null bs=4096 count=1

Signed-off-by: MITSUNARI Shigeo <herumi at nifty.com>
Cc: Al Viro <viro at zeniv.linux.org.uk>
Cc: Jeff Moyer <jmoyer at redhat.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/block_dev.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index c2bbe1f..db64e31 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1047,6 +1047,7 @@ int revalidate_disk(struct gendisk *disk)

 	mutex_lock(&bdev->bd_mutex);
 	check_disk_size_change(disk, bdev);
+	bdev->bd_invalidated = 0;
 	mutex_unlock(&bdev->bd_mutex);
 	bdput(bdev);
 	return ret;
--
1.8.1.2