high speed data to usb disk makes the kernel think that is has been unmounted

[Patrik Nilsson <nipatriknilsson@gmail.com>]

Hi!

I have an issue with a usb to sata adapter when much high speed data is 
sent. If I erase my 4Tb SSD disk connected to the usb to sata interface 
with a "slower" /dev/urandom it works, but if I exchanges this to 
/dev/zero the disk is after a while disconnected.

For logs from udev and more debug attempts see: 
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1886172

Description:

When the speed of data with a usb disk device is too high, the probes 
that check if the disk still exists is missed. This makes the disk to be 
unmounted and is remounted with an other drive letter (/dev/sdX). If 
this disk is the root ("/"), the computer hangs.

A usb SSD-disk (4 TB) connected to a USB port reproduce this bug easily. 
This has never happened with a mechanical USB-drive.

Symptoms and how to reproduce:

1) (Disk mounted as root) Computer hangs. Only way to get started again 
is a hard reset.

2) (Erasing disk, not mounted as root) If you erase a disk with dd ("dd 
if=/dev/zero of=/dev/sdX"), the disk disappears from the mounted list 
and reappears as an other drive letter. In my case the data is 
redirected to /dev/null and the fans speed up. The apparent data 
transfer speed is also increased. Usually this happens after about 45 to 
60 minutes.

3) Fill RAM with programs and make sure the swap to this disk is used.

Bug found in:

$ uname -a
Linux pb-189b1884 5.4.0-40-generic #44-Ubuntu SMP Tue Jun 23 00:01:04 
UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

$ cat /proc/version_signature
Ubuntu 5.4.0-40.44-generic 5.4.44

Hardware:

Tested with slower and faster computers. Tested directly connected to a 
computer and via a hub. They all reproduce this bug.

Workaround:

None found.

Best regards,
Patrik