On 13.09.2018 11:34, Jürgen Herrmann wrote:
> Hello!
>
> I have a newly installed laptop running a freshly installed (abt. two
> months ago) laptop running latest linux mint 19. Root filesystem is on a
> 1TB Samsung 860 M.2 SSD with btrfs on top of a LUKS encrypted 900G
> partition. Timeshift-btrfs is enabled for root (@) and home (@home)
> subvolumes. I want to transfer snapshots to a server with a separated
> disk via "btrfs send" and ssh.
>
> Here's the list of snapshot directories, each containing tow snapshots
> for root and home:
>
> drwxr-xr-x 1 root root 30 Sep 12 22:08 2018-08-16_20-00-01
> drwxr-xr-x 1 root root 30 Aug 17 14:00 2018-08-17_14-00-02
> drwxr-xr-x 1 root root 30 Aug 23 20:00 2018-08-23_20-00-01
> drwxr-xr-x 1 root root 30 Aug 30 20:00 2018-08-30_20-00-01
> drwxr-xr-x 1 root root 30 Sep 6 20:00 2018-09-06_20-00-01
> drwxr-xr-x 1 root root 30 Sep 6 22:00 2018-09-06_22-00-01
> drwxr-xr-x 1 root root 30 Sep 8 16:00 2018-09-08_16-00-01
> drwxr-xr-x 1 root root 30 Sep 10 20:00 2018-09-10_20-00-02
> drwxr-xr-x 1 root root 30 Sep 11 21:00 2018-09-11_21-00-02
> drwxr-xr-x 1 root root 30 Sep 12 21:00 2018-09-12_21-00-01
>
> "btrfs send
> /mnt/timeshift/backup/timeshift-btrfs/snapshots/2018-08-16_20-00-01/@
>>/dev/null" results in the btrfs task taking 100% cpu time on one cpu
> and then all IO is blocked -> only reboot can solve the hang.
>
> The crash does not happen immediately, as i was on the road using
> cellular connection it seemed fine at first. That's how I found out that
> it transfers ~140MB of data before hanging. The snapshot is created on
> the server and contains data (du shows abt 140MB).
>
> I am running vanilla kernel 4.18.6 (compiled by myself) and btrfs progs
> 4.17.1 compiled from source.
>
> Here's the btrfs filesystem info:
> Label: none uuid: a914c141-72bf-448b-847f-d64ee82d8b7b
> Total devices 1 FS bytes used 342.85GiB
> devid 1 size 875.44GiB used 357.05GiB path
> /dev/mapper/sda3_crypt
>
> A scrub shows no errors:
> scrub status for a914c141-72bf-448b-847f-d64ee82d8b7b
> scrub started at Thu Sep 13 10:20:18 2018 and finished after
> 00:12:19
> total bytes scrubbed: 342.78GiB with 0 errors
>
> What can I do to help debugging this issue?
You should provide output of echo w > /proc/sysrq-trigger. Also
sample the stack of /proc/[pid of btrfs send]/stack to see if it is
changing.
>
> Best regards,
> Jürgen
