Re: infinite loop with 36 Byte inquiry (sbp2 regression in 2.6.14-rcX)

[James Bottomley <James.Bottomley@SteelEye.com>]

On Sun, 2005-10-23 at 02:33 +0200, Stefan Richter wrote:
> I just noticed that devices which require sbp2's inquiry hack are not 
> usable anymore. I don't know when the regression crept in since I don't 
> remember when I used the affected device successfully the last time. One 
> thing is for sure: The code change which triggered the regression took 
> not place in sbp2 itself.
> 
> The device in question is an older 2.5" FireWire disk, DViCO Momobay 
> CX-1. What happens under Linux 2.6.14-rc5 is this: Without debug logging 
> turned on, it seems as if the process which started the sbp2 probe 
> (knodemgrd or modprobe) is hanging in D state. But debug logging enabled 
> in sbp2 reveals that it isn't locked up but rather caught in a loop, 
> sending inquiry commands:
> 
> > Oct 23 01:26:59 shuttle kernel: ieee1394: sbp2: sbp2_module_init
> > Oct 23 01:26:59 shuttle kernel: sbp2: $Rev: 1306 $ Ben Collins <bcollins@debian.org>
> > Oct 23 01:26:59 shuttle kernel: ieee1394: sbp2: sbp2_probe
> > Oct 23 01:26:59 shuttle kernel: ieee1394: sbp2: sbp2_alloc_device
> > Oct 23 01:26:59 shuttle kernel: ieee1394: sbp2: sbp2_alloc_device: allocated hostinfo
> > Oct 23 01:26:59 shuttle kernel: scsi0 : SCSI emulation for IEEE-1394 SBP-2 Devices
> > Oct 23 01:26:59 shuttle kernel: ieee1394: sbp2: sbp2_parse_unit_directory
> > Oct 23 01:26:59 shuttle kernel: ieee1394: sbp2: sbp2_management_agent_addr = f0010000
> > Oct 23 01:26:59 shuttle kernel: ieee1394: sbp2: sbp2_unit_characteristics = a08
> > Oct 23 01:26:59 shuttle kernel: ieee1394: sbp2: sbp2_command_set_spec_id = 609e
> > Oct 23 01:26:59 shuttle kernel: ieee1394: sbp2: sbp2_command_set = 104d8
> > Oct 23 01:26:59 shuttle kernel: ieee1394: sbp2: sbp2_firmware_revision = 2800
> > Oct 23 01:26:59 shuttle kernel: ieee1394: sbp2: Node 1-01:1023: Using 36byte inquiry workaround

I don't see any looping in the traces, could you characterise what's
going on for those of us who haven't fully explored the sbp2 driver?

However, at a brief examination it looks like you do quite a lot of
response snooping.  This always was broken for commands from userspace,
but it's completely broken now we only use scatter/gather commands from
block.

Secondly, I don't think your inquiry hack is effective any more, because
you try to alter request_bufflen, which doesn't carry the length of a
s/g command.

We have a device flag: BLIST_INQUIRY_36 which restricts the named
devices only to having 36 byte inquiries sent.  Could your internal
table be migrated up to the mid-layer list to avoid the issue
altogether?

James


James