Re: [PATCH] libata: fix SCSI/ATA device association during hotplug, take 2

[Jeff Garzik <jeff@garzik.org>]

Tejun Heo wrote:
> Two subtle hotplug related bugs are found.
> 
> * SCSI didn't use to issue commands to devices in SDEV_CANCEL state
>   but now it does.  For ATA devices, it means that SYNCHRONIZE_CACHE
>   is issued even after libata tells SCSI midlayer that the SCSI device
>   is offline now.  When devices are swapped, SYNCHRONIZE_CACHE for the
>   previous device can be issued to the later device.
> 
> * Devices can be swapped while SCSI probing is in progress.  SCSI
>   device used to get associated with ATA device only after probing is
>   complete, which means that SCSI device detaching is not performed
>   while probing.  This can result in mismatch between SCSI device and
>   ATA device (e.g. sd attached to ATAPI device) if devices are
>   swapped after INQUIRY but before probing is complete.
> 
> This patch makes libata associate new SCSI device with ATA device
> before INQUIRY is issued and check whether SCSI device issuing a
> command matches dev->sdev on each command.  Both bugs are fixed by
> this tighter coupling between SCSI device and ATA device.
> 
> Signed-off-by: Tejun Heo <htejun@gmail.com>
> Cc: Mark Lord <liml@rtr.ca>
> ---
> 
> scsi_dev <-> ata_dev association is moved to ->slave_alloc as Mark
> suggested.
[...]
> +		/* Try to attach new SCSI device.  SCSI midlayer
> +		 * doesn't supply separate interfaces for allocating
> +		 * and probing, so in this function, we can associate
> +		 * new SCSI device with its target ATA device only
> +		 * after probing is complete.
> +		 *
> +		 * However, hotplug event may occur during probing and
> +		 * we might have to detach a SCSI device which is in
> +		 * the middle of probing.  So, we need to associate
> +		 * new SCSI device with its target ATA device before
> +		 * the first INQUIRY is complete.
> +		 *
> +		 * This is achieved by attaching the device in
> +		 * ->slave_alloc().
> +		 */
> +		scsi_add_device(ap->scsi_host, 0, i, 0);

ACK

The above quoted comment serves to reinforce that libata eventually 
needs to have an ATA transport class