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