Re: "btrfs: harden agaist duplicate fsid" spams syslog

[Anand Jain <anand.jain@oracle.com>]

Right. It happened even without this patch but we just know it now.

In the original investigations of the patch, the moment you copy a
device image into another device, the autoscan would scan the new
device into the btrfs kernel and created a mess. Now with this patch
we won't replace the device path unless it's the same device (and we
have to let that happen).

Now the question I am trying to understand, why same device is being
scanned every 2 mins, even though its already mount-ed. I am guessing
its toggling the same device paths trying to mount the device-path
which is not mounted. So autofs's check for the device mount seems to
be path based.

Would you please provide your LVM configs and I believe you are using
dm-mapping too. What are the device paths used in the fstab and in grub.
And do you see these messages for all devices of
4d1ba5af-8b89-4cb5-96c6-55d1f028a202 or just devid 4? Would you please
provide more logs at least a complete cycle of the repeating logs.

-Anand


On 11/7/19 2:49 AM, Graham Cobb wrote:
> Anand's Nov 2018 patch "btrfs: harden agaist duplicate fsid" has
> recently percolated through to my Debian buster server system.
> 
> And it is spamming my log files.
> 
> Each of my btrfs filesystem devices logs 4 messages every 2 minutes.
> Here is an example of the 4 messages related to one device:
> 
> Jul 10 19:32:27 black kernel: [33017.407252] BTRFS info (device sdc3):
> device fsid 4d1ba5af-8b89-4cb5-96c6-55d1f028a202 devid 4 moved
> old:/dev/mapper/cryptdata4tb--vg-backup new:/dev/dm-13
> Jul 10 19:32:27 black kernel: [33017.522242] BTRFS info (device sdc3):
> device fsid 4d1ba5af-8b89-4cb5-96c6-55d1f028a202 devid 4 moved
> old:/dev/dm-13 new:/dev/mapper/cryptdata4tb--vg-backup
> Jul 10 19:32:29 black kernel: [33018.797161] BTRFS info (device sdc3):
> device fsid 4d1ba5af-8b89-4cb5-96c6-55d1f028a202 devid 4 moved
> old:/dev/mapper/cryptdata4tb--vg-backup new:/dev/dm-13
> Jul 10 19:32:29 black kernel: [33019.061631] BTRFS info (device sdc3):
> device fsid 4d1ba5af-8b89-4cb5-96c6-55d1f028a202 devid 4 moved
> old:/dev/dm-13 new:/dev/mapper/cryptdata4tb--vg-backup
> 
> What is happening here is that each device is actually an LVM logical
> volume, and it is known by a /dev/mapper name and a /dev/dm name. And
> every 2 minutes something cause btrfs to notice that there are two names
> for the same device and it swaps them around. Logging a message to say
> it has done so. And doing it 4 times.
> 
> I presume that the swapping doesn't cause any problem. I wonder slightly
> whether ordering guarantees and barriers all work correctly but I
> haven't noticed any problems.
> 
> I also assume it has been doing this for a while -- just silently before
> this patch came along.
> 
> Is btrfs noticing this itself or is something else (udev or systemd, for
> example) triggering it?
> 
> Should I worry about it?
> 
> Is there any way to not have my log files full of this?
> 
> Graham
> 
> [This started with a Debian testing kernel a couple of months ago.
> Current uname -a gives: Linux black 4.19.0-5-amd64 #1 SMP Debian
> 4.19.37-5 (2019-06-19) x86_64 GNU/Linux]
>