No boot or access of single NVME SSD with BTRFS possible

No boot or access of single NVME SSD with BTRFS possible

[Thomas Michael Engelke]

This morning I booted my system up, and I found this message:

Starting systemd-udevd, version 252.2-3-arch
mount: /new_root: mount(2) system call failed: File exists.
dmesg(1) may have more information after failed mount system call
You are now dropped into an emergency shell
sh: can't access tty: job control turned off

I have regular snapshots, but booting into any of them results in the 
same message. I therefor booted a live USB and tried to access the BTRFS 
volume, but no luck:

[liveuser@eos-2021.12.17 ~]$ time sudo mount -t btrfs /dev/nvme0n1p2 
/mnt
mount: /mnt: mount(2) system call failed: File exists.

real	0m1.415s
user	0m0.006s
sys	0m0.179s
[liveuser@eos-2021.12.17 ~]$

Note the hang time, I'm not sure it is relevant.

/mnt is not mounted at the moment:

[liveuser@eos-2021.12.17 ~]$ sudo umount /mnt
umount: /mnt: not mounted.
[liveuser@eos-2021.12.17 ~]$ sudo mount -t btrfs /dev/nvme0n1p2 /mnt -o 
subvol=@
mount: /mnt: mount(2) system call failed: File exists.
[liveuser@eos-2021.12.17 ~]$

A check reports everything in order:

[liveuser@eos-2021.12.17 ~]$ sudo btrfs check --check-data-csum -p 
/dev/nvme0n1p2
Opening filesystem to check...
Checking filesystem on /dev/nvme0n1p2
UUID: 21b3cc23-6e76-45bf-acd2-d99dc24cc0d8
[1/7] checking root items                      (0:00:02 elapsed, 2083036 
items checked)
[2/7] checking extents                         (0:00:13 elapsed, 244780 
items checked)
[3/7] checking free space cache                (0:00:00 elapsed, 1148 
items checked)
[4/7] checking fs roots                        (0:00:29 elapsed, 147302 
items checked)
[5/7] checking csums against data              (0:10:28 elapsed, 712198 
items checked)
[6/7] checking root refs                       (0:00:00 elapsed, 30 
items checked)
[7/7] checking quota groups                    (0:00:24 elapsed, 1843328 
items checked)
found 1174419738624 bytes used, no error found
total csum bytes: 1141823932
total tree bytes: 4009918464
total fs tree bytes: 2423521280
total extent tree bytes: 225329152
btree space waste bytes: 732619798
file data blocks allocated: 2454781140992
  referenced 1403791265792
[liveuser@eos-2021.12.17 ~]$

I have not done any writes to the device, I wanted to wait with that 
until I have a clearer picture of what is wrong.

Required information for the live USB boot:

uname -a: Linux EndeavourOS 5.15.8-arch1-1 #1 SMP PREEMPT Tue, 14 Dec 
2021 12:28:02 +0000 x86_64 GNU/Linux
btrfs --version: btrfs-progs v5.15.1
sudo btrfs fi show:

Label: none  uuid: 21b3cc23-6e76-45bf-acd2-d99dc24cc0d8
	Total devices 1 FS bytes used 1.07TiB
	devid    1 size 1.83TiB used 1.12TiB path /dev/nvme0n1p2

Link to the dmesg parts I though were relevant (from the live USB): 
https://forum.endeavouros.com/t/btrfs-file-system-unmountable-no-boot-and-access-possible/34586?u=dromundkaas