Re: 2.6.19-rc3 system freezes when ripping with cdparanoia at ioctl(SG_IO)

[Jeff Garzik <jgarzik@pobox.com>]

Tejun Heo wrote:
> This works for most PATA ATAPI devices.  Most devices detect reversed 
> transfer and terminate the command promptly.  But this doesn't seem to 
> be true for SATA device.  Many just hang and time out commands with the 
> wrong transfer direction.  If you consider that most early SATA ATAPI 
> devices are actually PATA + bridge, this is sorta inevitable.  The 
> PATA-SATA bridge cannot issue D2H FIS to abort the command by itself. 
> It's just mirroring the status of PATA side and PATA side doesn't know 
> SATA protocol mismatch has occurred.
>
> So, IDENTIFY w/ write-DMA protocol times out after quite some seconds. 
> This is where things go worse from bad.  SATA controllers which have 
> shadow TF registers don't handle timeout conditions very well, 
> especially when they're waiting for data transfer.  They basically hold 
> the PCI bus and hang till the transfer completes (which never happens). 
>  That's where the hard lock up comes from.
>
> Jens, I think we need to match block sg's behavior to SCSI's.  Monty, 
> the timeout and hard lock up are due to hardware restrictions.  Kernel 
> and libata can't do much about it.  So, please find other way to detect 
> interface.


Mapping 'bidirectional' is a bit difficult.  It might be reasonable to 
interpret that as "userspace doesn't know" at lower layers, and then 
fill in a data transfer direction based on ATA command opcode.

Given that there are stupid apps/libs out there in the field with this 
behavior, even if the apps are fixed I think we are stuck with the 
stupidities.  At the very least, we could abort commands that transfer 
data in the opposite direction from indicated, based on a command opcode 
table.

	Jeff


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