bdev size not updated correctly after underlying device is resized

[Andrew Patterson <andrew.patterson@hp.com>]

I ran into this problem while trying to resize a mounted file-system
after growing/shrinking the size of the underlying block device (in this
case, a fibre-channel LUN). The kernel recognizes the device size change
when revalidate_disk() is called, but the bdev->bd_inode->i_size will
not be updated for any new openers if there are already openers of the
device.  In my case I was using LVM thusly:

     1. Create a volume group with a physical volume on something that
        can be resized (usually some sort of SCSI RAID device).
     2. Create a logical volume on that VG.  This holds the underlying
        PV block device open as long at the LV is activated
     3. Run blockdev --getsize <block dev>
     4. Resize the underlying block device.
     5. Get the OS to notice the change.  For fibre-channel LUN's you
        can use /sys/class/scsi_device/<device>/device/rescan.
     6. Size is correctly changed in /dev/block/<device>/size
     7. Run blockdev --getsize again (no change in size reported)
     8. Inactivate the LV (there are now no longer any openers on the
        block device)
     9. Run blockdev --getsize again.  Size is now correct as there are
        no openers on the device when blockdev is run.

This problem has been reported before at:

  http://lkml.org/lkml/2007/7/3/83

The following patch is a suggestion on how to fix this problem.  It is
not a complete solution as it is probably a bad thing to change other
openers device size without at least protecting the change with a lock.
And user-apps and other sub-systems might not like the reported device
size being changed underneath them. It looks like the following
sub-systems access this value:

ndb
dm
md
affs
hfs
jfs
reiserfs
udf


Subject: [PATCH] Reset bdev size regardless of other openers.

A block device may be resized while online.  If the revalidate_disk
routine is called after the resize, the gendisk->capacity value is
updated for the device.  However, the bdev->bd_inode->i_size is not
updated when the block device is opened if there are any other openers
on the device.  This means that apps like LVM are unlikely to see the
size change as they tend to keep their block devices open.  There is a
discussion of this problem at:

  http://lkml.org/lkml/2007/7/3/83

This patch changes block_dev.c:do_open() to call bd_set_size()
regardless if there are other openers on the device.  It should not be
applied in its existing state as changing i_size should be protected by
a lock. Also, there needs to be some analysis on the effects of changing
the device size underneath an app.

Andrew Patterson

Subject: [PATCH] Reset bdev size regardless of other openers.

A block device may be resized while online.  If the revalidate_disk
routine is called after the resize, the gendisk->capacity value is
updated for the device.  However, the bdev->bd_inode->i_size is not
updated when the block device is opened if there are any other openers
on the device.  This means that apps like LVM are unlikely to see the
size change as they tend to keep their block devices open.  There is a
discussion of this problem at:

  http://lkml.org/lkml/2007/7/3/83

This patch changes block_dev.c:do_open() to call bd_set_size()
regardless if there are other openers on the device.  It should not be
applied in its existing state as changing i_size should be protected by
a lock. Also, there needs to be some analysis on the effects of changing
the device size underneath an app.

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 7d822fa..d13a4e5 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -992,6 +992,9 @@ static int do_open(struct block_device *bdev, struct file *file, int for_part)
 				ret = bdev->bd_disk->fops->open(bdev->bd_inode, file);
 				if (ret)
 					goto out;
+				/* device may have been resized with revalidate_disk */
+				if (!part)
+					bd_set_size(bdev, (loff_t)get_capacity(disk)<<9);
 			}
 			if (bdev->bd_invalidated)
 				rescan_partitions(bdev->bd_disk, bdev);