[REGRESSION 3.17] scsi (uas) disks no longer using tagged command queuing

[Hans de Goede <hdegoede@redhat.com>]

Hi All,

While working on making error handling in the uas driver more robust,
I noticed that all the commands being send to a sata ssd hooked up
over uas were untagged, where I would expect tcq to be used, as that
is the big advantage of uas over usb-storage / bot.

Taking the uas.c file from 3.17, and building it for 3.16 restores
the use of tcq (debugged by adding a printk blk_rq_tagged + request->tag).

So either uas is doing something wrong which happened to work in
3.16, or something has broken in 3.17.

I've already added debug printk-s of scsi_device->tagged_supported,
queue_depth, ordered_tags and simple_tags and those all look good
(1, 29, 1, 1).

I've also tried setting disable_blk_mq and that does not help.

Any hints to help debugging this further (other then a bisect) are
appreciated. If no-one has any smart ideas I guess I'll end up doing
a full bisect.

Regards,

Hans