linux-ext4 - Re: ext4_orphan_cleanup errors during mount a LVM snapshot

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Message-Id: <1804D95E-CD91-41A3-8177-E3E585C9E1E6@dilger.ca>
Date:	Wed, 16 Apr 2014 10:33:22 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Wayne Chou <gmmark12@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: ext4_orphan_cleanup errors during mount a LVM snapshot

On Apr 16, 2014, at 2:46 AM, Wayne Chou <gmmark12@...il.com> wrote:
> I create a LVM snapshot from a mounted ext4 file system by:
> "lvcreate -kn --snapshot --name snap1 /dev/mapper/vg1/lv1"
> 
> And after I mount this snapshot to another folder like:
> "mount -t ext4 /dev/mapper/vg1-snap1 /mnt/test"
> the following messages prompted in dmesg:
> 
> [ 2445.480908] EXT4-fs (dm-6): orphan cleanup on readonly fs
> [ 2445.502317] EXT4-fs (dm-6): ext4_orphan_cleanup: deleting
> unreferenced inode 131180
> [ 2445.502355] EXT4-fs (dm-6): ext4_orphan_cleanup: deleting
> unreferenced inode 131176
> [ 2445.502360] EXT4-fs (dm-6): ext4_orphan_cleanup: deleting
> unreferenced inode 131175
> [ 2445.502366] EXT4-fs (dm-6): ext4_orphan_cleanup: deleting
> unreferenced inode 131174
> [ 2445.502372] EXT4-fs (dm-6): ext4_orphan_cleanup: deleting
> unreferenced inode 131173
> [ 2445.502376] EXT4-fs (dm-6): 5 orphan inodes deleted

The first question is whether you are experiencing any actual problems
as a result of the orphan inode cleanup?  This is normal behaviour if
there are applications with open-unlinked files when the snapshot is taken,
or if the system crashes at this point.  The orphan cleanup will free up
these open-unlinked inodes and their blocks at mount time, keeping the
filesystem consistent.

> To find out what the reason is, I use 'lsof' on lv1's mount point before I take
> the snapshot.  Then I got some MySQL services that opened these temporary files
> which causes the orphan inodes in LVM snapshots:
> mysqld    26257 admin    7u   REG  253,5        0 131173
> /LV1/.system/tmp/ibTidhzb (deleted)
> mysqld    26257 admin    8u   REG  253,5        0 131174
> /LV1/.system/tmp/ibgWhCYc (deleted)
> mysqld    26257 admin    9u   REG  253,5        0 131175
> /LV1/.system/tmp/ibJE5pne (deleted)
> mysqld    26257 admin   10u   REG  253,5        0 131176
> /LV1/.system/tmp/ibsvL9hg (deleted)
> mysqld    26257 admin   14u   REG  253,5        0 131180
> /LV1/.system/tmp/ibcz1qOM (deleted)
> 
> 
> From the above investigation, the problem gets solved if I
> disable the MySQL service before taking the LVM snapshot.
> 
> However, I wonder if there's any other way to solve this issue.
> For example, can I just blindly remove these orphan inodes when
> ext4_freeze() is called?  Thank you.

What problem needs to be solved?  Is it just the printing of these
error messages that is confusing, or something else?

Cheers, Andreas






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