[SCSI] uas: disable use of blk-mq I/O path

The uas driver uses the block layer tag for USB3 stream IDs.  With
blk-mq we can get larger tag numbers that the queue depth, which breaks
this assumption.  A fix is under way for 3.18, but sits on top of
large changes so can't easily be backported.   Set the disable_blk_mq
path so that a uas device can't easily crash the system when using
blk-mq for SCSI.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
index 3f42785f653c..9bfa7252f7f9 100644
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -970,6 +970,13 @@ static struct scsi_host_template uas_host_template = {
         .cmd_per_lun = 1,       /* until we override it */
         .skip_settle_delay = 1,
         .ordered_tag = 1,
+
+        /*
+         * The uas drivers expects tags not to be bigger than the maximum
+         * per-device queue depth, which is not true with the blk-mq tag
+         * allocator.
+         */
+        .disable_blk_mq = true,
 };
 
 #define UNUSUAL_DEV(id_vendor, id_product, bcdDeviceMin, bcdDeviceMax, \