[src/trunk]: src/sys/dev/usb Tweak locking rule. Fix broken unlocked rmw.

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/f8a93a139304
branches:  trunk
changeset: 353013:f8a93a139304
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Mon Apr 17 09:16:13 2017 +0000

description:
Tweak locking rule.  Fix broken unlocked rmw.

diffstat:

 sys/dev/usb/ualea.c |  12 +++++-------
 1 files changed, 5 insertions(+), 7 deletions(-)

diffs (39 lines):

diff -r 3b92fdf56b40 -r f8a93a139304 sys/dev/usb/ualea.c
--- a/sys/dev/usb/ualea.c       Mon Apr 17 09:06:55 2017 +0000
+++ b/sys/dev/usb/ualea.c       Mon Apr 17 09:16:13 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: ualea.c,v 1.1 2017/04/17 08:59:37 riastradh Exp $      */
+/*     $NetBSD: ualea.c,v 1.2 2017/04/17 09:16:13 riastradh Exp $      */
 
 /*-
  * Copyright (c) 2017 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: ualea.c,v 1.1 2017/04/17 08:59:37 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: ualea.c,v 1.2 2017/04/17 09:16:13 riastradh Exp $");
 
 #include <sys/types.h>
 #include <sys/atomic.h>
@@ -55,11 +55,7 @@
        struct usbd_xfer        *sc_xfer;
        bool                    sc_attached:1;
        bool                    sc_inflight:1;
-       /*
-        * attached true->false only under lock
-        * inflight false->true only under lock
-        * issue xfer only under lock, if attached=true and inflight=false
-        */
+       /* lock covers sc_attached, sc_inflight, and usbd_transfer(sc_xfer) */
 };
 
 static int     ualea_match(device_t, cfdata_t, void *);
@@ -228,5 +224,7 @@
 
 out:
        /* Allow subsequent transfers.  */
+       mutex_enter(&sc->sc_lock);
        sc->sc_inflight = false;
+       mutex_exit(&sc->sc_lock);
 }