CVS commit: src/sys/dev/usb

["Taylor R Campbell" <riastradh%netbsd.org@localhost>]

Module Name:    src
Committed By:   riastradh
Date:           Sat May 14 19:44:26 UTC 2022

Modified Files:
        src/sys/dev/usb: xhci.c

Log Message:
xhci(4): Fix edge case in simultaneous xfer abort and failure.

On successful usbd_xfer_trycomplete, caller must set ux_status and
call usb_transfer_complete before releasing the pipe (bus) lock.
Failing to call usb_transfer_complete is a mistake.  Presumably this
was intended to claim the xfer to complete it only on the last
packet.

I previously introduced the violation of this rule when the code
looked like

        xfer->ux_status = err;
        if (trb stuff)
                usb_transfer_complete(xfer);

I mostly mechanically changed all the assignments of xfer->ux_status
to do usbd_xfer_trycomplete first and then usb_transfer_complete.

In the original, the extra assignment of xfer->ux_status in the event
we _don't_ immediately call usb_transfer_complete was likely
redundant and (except insofar as the abort protocol was broken)
harmless.  But now it is a problem because of the contract between
usbd_xfer_trycomplete and usb_transfer_complete under the pipe (bus)
lock.  In retrospect, the original probably should have been

        if (trb stuff) {
                xfer->ux_status = err;
                usb_transfer_complete(xfer);
        }

and my mechanical transformation should have worked, but also in
retrospect I should have put more thought into the change and done it
a little less mechanically.


To generate a diff of this commit:
cvs rdiff -u -r1.164 -r1.165 src/sys/dev/usb/xhci.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.