Re: linux-next: pata_acpi.ko crashes at ata_ap_acpi_handle()

[Jeff Garzik <jeff@garzik.org>]

On 02/24/2012 09:26 AM, Alan Cox wrote:
>>         We can see the code in ata_ap_acpi_handle()accesses ap->scsi_host filed without checking if it’s initialized, which causes NULL pointer panic. Meanwhile, ata_pci_sff_activate_host() calls ata_host_register(), which calls ata_scsi_add_hosts() to initialize scsi_host field. Both calls are after ata_host_start() in a must-visit code path. I believe ata_scsi_add_hosts() is the first place for initialization because it does not check if scsi_host field is NULL either. So it makes no sense to access ap->scsi_host in ata_ap_acpi_handle().
>
> This appears to be caused by broken changes to the libata code from
> Matthew Garrett and others who introduced a dependancy on scsi_host which
> isn't safe to do because drivers can touch the ACPI earlier than the
> scsi registration and in fact *NEED* to do so.
>
> Jeff - can we get these patches dropped back out for the moment - they
> cause a regression and boot crash in pata_acpi.
>
> The stack from 75d22cd567cac6fe2af8acb33f6ebcd16876d250 needs to get
> punted and the scsi_host indirection removed and fixed up for it to work
> safely with existing libata drivers.
>
> I don't see an obvious way to fix up the existing ordering dependancies,
> especially on the pata_acpi side but if someone has bright ideas there
> that would probably be the best choice. Right now these patches stop any
> ACPI querying being done during the port setup. We need to do those
> queries in order to know if the port can be driven by ACPI and what modes
> we can make work.

Sigh.  You are right.  I kept waiting and waiting for fix-up patches, 
but they just need more baking and thinking it seems.

	Jeff