[src/trunk]: src/sys/dev/usb usbnet: Fix ordering of actions in usbnet_stop.

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

details:   https://anonhg.NetBSD.org/src/rev/78dddfe76e0f
branches:  trunk
changeset: 362495:78dddfe76e0f
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Thu Mar 03 05:48:22 2022 +0000

description:
usbnet: Fix ordering of actions in usbnet_stop.

Make sure all software activity is quiescent (callouts and tasks,
including ifmedia and mii callbacks -- anything that might trigger
register access) before asking the driver to stop the hardware.  This
way, the driver uno_stop routine is guaranteed exclusive access to
the registers.

This will also enable us to simplify the callouts and tasks so they
don't have to check the software state -- to be done in a separate
commit.

diffstat:

 sys/dev/usb/usbnet.c |  25 +++++++++++++++++++------
 1 files changed, 19 insertions(+), 6 deletions(-)

diffs (52 lines):

diff -r a5421d75b5e9 -r 78dddfe76e0f sys/dev/usb/usbnet.c
--- a/sys/dev/usb/usbnet.c      Thu Mar 03 05:48:14 2022 +0000
+++ b/sys/dev/usb/usbnet.c      Thu Mar 03 05:48:22 2022 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: usbnet.c,v 1.55 2022/03/03 05:48:14 riastradh Exp $    */
+/*     $NetBSD: usbnet.c,v 1.56 2022/03/03 05:48:22 riastradh Exp $    */
 
 /*
  * Copyright (c) 2019 Matthew R. Green
@@ -31,7 +31,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: usbnet.c,v 1.55 2022/03/03 05:48:14 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: usbnet.c,v 1.56 2022/03/03 05:48:22 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/kernel.h>
@@ -1132,16 +1132,29 @@
        mutex_exit(&unp->unp_txlock);
        mutex_exit(&unp->unp_rxlock);
 
+       /*
+        * Stop the timer first, then the task -- if the timer was
+        * already firing, we stop the task or wait for it complete
+        * only after if last fired.  Setting unp_stopping prevents the
+        * timer task from being scheduled again.
+        */
+       callout_halt(&unp->unp_stat_ch, &unp->unp_core_lock);
+       usb_rem_task_wait(un->un_udev, &unp->unp_ticktask, USB_TASKQ_DRIVER,
+           &unp->unp_core_lock);
+
+       /*
+        * Now that the software is quiescent, ask the driver to stop
+        * the hardware.  The driver's uno_stop routine now has
+        * exclusive access to any registers that might previously have
+        * been used by to ifmedia, mii, or ioctl callbacks.
+        */
        uno_stop(un, ifp, disable);
 
+       /* Clear the watchdog timer.  */
        mutex_enter(&unp->unp_txlock);
        unp->unp_timer = 0;
        mutex_exit(&unp->unp_txlock);
 
-       callout_halt(&unp->unp_stat_ch, &unp->unp_core_lock);
-       usb_rem_task_wait(un->un_udev, &unp->unp_ticktask, USB_TASKQ_DRIVER,
-           &unp->unp_core_lock);
-
        /* Stop transfers. */
        usbnet_ep_stop_pipes(un);