[Bug 28647] sbp2 hot plug causes hard crashes

[Ryan Lortie]

Public bug reported:
https://launchpad.net/malone/bugs/28647

Affects: linux-source-2.6.15 (Ubuntu)
       Severity: Normal
       Priority: (none set)
         Status: Unconfirmed

Description:
it seems that if the system is busy when you hotplug sbp2 devices it can
lead to hard crashes.  this can happen both when plugging and
unplugging.

my firewire bus is setup as follows:

computer (moonpix) is connected to a hub.
hub has one empty port (cable connected) and one port connected via a 6-to-4 cable to the 4pin port of my sony dvd burner.
the 6pin port on the sony dvd drive is connected to a 6pin port on a generic enclosure.

the enclosure contains a maxtor harddrive.

when i turn the enclosure on the kernel properly detects the drive and
udev makes entries in /dev for it (/dev/sdd, /dev/sdd1).  the device
does not show up in hal, however, and does not get automounted.

i wondered what had happened and decided to try it again so i turned the
drive off (using the power switch on the enclosure) and turned it back
on again fairly quickly.  my system locked hard (X stopped responding,
no keyboard, no ssh, no ping).

i'm running custom-compiled ieee1394 code from an unstable branch so i
thought this might be the problem.  i rebooted and tried the normal
ubuntu code but it dies too.

in an attempt to see what dmesg says just before the system locks up i
dropped down to the console and did a lot of 'dmesg | tail'.  this takes
a while to display (because the framebuffer console is slow) so i
pressed up-enter-up-enter a lot of times to queue up a bunch of them.  i
turned the drive on while this was happening and the system froze.  this
produced a rather spectacular effect (screenshot attached).

once when rebooting i noticed that the drive was on so i turned it off.
this was right around "loading hardware abstraction layer" and the
system hung solid as soon as i turned the drive off.

so i get hangs in the following situations:

- turning the drive on shortly after turning it off
- turning the drive on when fbcon is busy writing text
- turning the drive off during bootup

the hangs happen with both the stock kernel firewire code and the
development branch code.