Re: 4.14 balance: kernel BUG at /home/kernel/COD/linux/fs/btrfs/ctree.c:1856!

[Hans van Kranenburg <hans.van.kranenburg@mendix.com>]

On 11/18/2017 12:48 PM, Hans van Kranenburg wrote:
> 
> So, who wants to help?
> 
> 1. Find a test system that you can crash.
> 2. Create a test filesystem with some data.
> 3. Run with 4.14? (makes the most sense I think)
> 4. Continuously feed the data to balance and send everything to /dev/null
> 5. Collect stack traces and borken filesystem images.

Ok, what I just did:

-# mkfs.btrfs --nodiscard /dev/xvdb
-# mount -o noatime /dev/xvdb /btrfs
-# cd btrfs/
-# btrfs sub create usr
-# rsync -av /usr/ usr/
-# btrfs sub snap -r usr/ usro

And then, both at the same time:

-# while true; do btrfs send usro/ > /dev/null; date; echo 3 >
/proc/sys/vm/drop_caches; done

and

-# while true; do btrfs balance start --full-balance /btrfs; done

After a few minutes we have the first error:


[ 1605.484627] BTRFS error (device xvdb): did not find backref in
send_root. inode=4260, offset=0, disk_byte=130793844736 found
extent=130793844736

Sat Nov 18 13:25:28 CET 2017
At subvol usro/
ERROR: send ioctl failed with -5: Input/output error

No big stack trace this time.

-- 
Hans van Kranenburg