[ 3.5.y.z extended stable ] Patch "nbd: fsync and kill block device on shutdown" has been added to staging queue

[Luis Henriques]

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

    nbd: fsync and kill block device on shutdown

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 c631ccd1b2c3c2f66039b818adc51f178972fc10 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini at redhat.com>
Date: Wed, 27 Feb 2013 17:05:25 -0800
Subject: [PATCH] nbd: fsync and kill block device on shutdown

commit 3a2d63f87989e01437ba994df5f297528c353d7d upstream.

There are two problems with shutdown in the NBD driver.

1: Receiving the NBD_DISCONNECT ioctl does not sync the filesystem.

   This patch adds the sync operation into __nbd_ioctl()'s
   NBD_DISCONNECT handler.  This is useful because BLKFLSBUF is restricted
   to processes that have CAP_SYS_ADMIN, and the NBD client may not
   possess it (fsync of the block device does not sync the filesystem,
   either).

2: Once we clear the socket we have no guarantee that later reads will
   come from the same backing storage.

   The patch adds calls to kill_bdev() in __nbd_ioctl()'s socket
   clearing code so the page cache is cleaned, lest reads that hit on the
   page cache will return stale data from the previously-accessible disk.

Example:

    # qemu-nbd -r -c/dev/nbd0 /dev/sr0
    # file -s /dev/nbd0
    /dev/stdin: # UDF filesystem data (version 1.5) etc.
    # qemu-nbd -d /dev/nbd0
    # qemu-nbd -r -c/dev/nbd0 /dev/sda
    # file -s /dev/nbd0
    /dev/stdin: # UDF filesystem data (version 1.5) etc.

While /dev/sda has:

    # file -s /dev/sda
    /dev/sda: x86 boot sector; etc.

Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
Acked-by: Paul Clements <Paul.Clements at steeleye.com>
Cc: Alex Bligh <alex at alex.org.uk>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
[ luis: adjust context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/block/nbd.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 3c4c225..7f25e24 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -584,12 +584,20 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 		struct request sreq;

 		dev_info(disk_to_dev(nbd->disk), "NBD_DISCONNECT\n");
+		if (!nbd->sock)
+			return -EINVAL;

+		mutex_unlock(&nbd->tx_lock);
+		fsync_bdev(bdev);
+		mutex_lock(&nbd->tx_lock);
 		blk_rq_init(NULL, &sreq);
 		sreq.cmd_type = REQ_TYPE_SPECIAL;
 		nbd_cmd(&sreq) = NBD_CMD_DISC;
+
+		/* Check again after getting mutex back.  */
 		if (!nbd->sock)
 			return -EINVAL;
+
 		nbd_send_req(nbd, &sreq);
                 return 0;
 	}
@@ -603,6 +611,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 		nbd_clear_que(nbd);
 		BUG_ON(!list_empty(&nbd->queue_head));
 		BUG_ON(!list_empty(&nbd->waiting_queue));
+		kill_bdev(bdev);
 		if (file)
 			fput(file);
 		return 0;
@@ -683,6 +692,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 		nbd->file = NULL;
 		nbd_clear_que(nbd);
 		dev_warn(disk_to_dev(nbd->disk), "queue cleared\n");
+		kill_bdev(bdev);
 		if (file)
 			fput(file);
 		nbd->bytesize = 0;
--
1.8.1.2