Re: [syzbot] [usb?] INFO: task hung in usb_port_suspend

Alan Stern
2024-10-13T14:30:25Z

On Sat, Oct 12, 2024 at 08:05:02PM -0700, syzbot wrote:
> Hello,
>
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> INFO: task hung in usb_register_dev

That wasn't particularly helpful. In fact, it gives the impression
that the problem is caused by something else, not a bad dequeue. None
of the tasks listed in the console log are waiting inside usb_kill_urb().

This time let's see all the enqueues, dequeues, and givebacks for
non-control URBs. I don't know that the problem is related to a
non-control URB, but I do know that a bunch of control URBs succeed so
it might help to keep the focus away from them.

Alan Stern

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing

Index: usb-devel/drivers/usb/gadget/udc/dummy_hcd.c
===================================================================
--- usb-devel.orig/drivers/usb/gadget/udc/dummy_hcd.c
+++ usb-devel/drivers/usb/gadget/udc/dummy_hcd.c
@@ -50,7 +50,7 @@
#define POWER_BUDGET 500 /* in mA; use 8 for low-power port testing */
#define POWER_BUDGET_3 900 /* in mA */

-#define DUMMY_TIMER_INT_NSECS 125000 /* 1 microframe */
+#define DUMMY_INT_KTIME ns_to_ktime(125000) /* 1 microframe */

static const char driver_name[] = "dummy_hcd";
static const char driver_desc[] = "USB Host+Gadget Emulator";
@@ -1301,10 +1301,12 @@ static int dummy_urb_enqueue(
dum_hcd->next_frame_urbp = urbp;
if (usb_pipetype(urb->pipe) == PIPE_CONTROL)
urb->error_count = 1; /* mark as a new urb */
+ else
+ dev_info(dummy_dev(dum_hcd), "Enqueue %p\n", urb);

/* kick the scheduler, it'll do the rest */
if (!hrtimer_active(&dum_hcd->timer))
- hrtimer_start(&dum_hcd->timer, ns_to_ktime(DUMMY_TIMER_INT_NSECS),
+ hrtimer_start(&dum_hcd->timer, DUMMY_INT_KTIME,
HRTIMER_MODE_REL_SOFT);

done:
@@ -1325,9 +1327,15 @@ static int dummy_urb_dequeue(struct usb_

rc = usb_hcd_check_unlink_urb(hcd, urb, status);
if (!rc && dum_hcd->rh_state != DUMMY_RH_RUNNING &&
- !list_empty(&dum_hcd->urbp_list))
- hrtimer_start(&dum_hcd->timer, ns_to_ktime(0), HRTIMER_MODE_REL_SOFT);
-
+ !list_empty(&dum_hcd->urbp_list)) {
+ if (usb_pipetype(urb->pipe) != PIPE_CONTROL)
+ dev_info(dummy_dev(dum_hcd), "Dequeue restart %p\n", urb);
+ hrtimer_start(&dum_hcd->timer, DUMMY_INT_KTIME,
+ HRTIMER_MODE_REL_SOFT);
+ } else if (usb_pipetype(urb->pipe) != PIPE_CONTROL) {
+ dev_info(dummy_dev(dum_hcd), "Dequeue norestart: %d %p\n",
+ rc, urb);
+ }
spin_unlock_irqrestore(&dum_hcd->dum->lock, flags);
return rc;
}
@@ -1984,6 +1992,8 @@ return_urb:
ep->already_seen = ep->setup_stage = 0;

usb_hcd_unlink_urb_from_ep(dummy_hcd_to_hcd(dum_hcd), urb);
+ if (usb_pipetype(urb->pipe) != PIPE_CONTROL)
+ dev_info(dummy_dev(dum_hcd), "Giveback %p\n", urb);
spin_unlock(&dum->lock);
usb_hcd_giveback_urb(dummy_hcd_to_hcd(dum_hcd), urb, status);
spin_lock(&dum->lock);
@@ -1995,8 +2005,7 @@ return_urb:
usb_put_dev(dum_hcd->udev);
dum_hcd->udev = NULL;
} else if (dum_hcd->rh_state == DUMMY_RH_RUNNING) {
- /* want a 1 msec delay here */
- hrtimer_start(&dum_hcd->timer, ns_to_ktime(DUMMY_TIMER_INT_NSECS),
+ hrtimer_start(&dum_hcd->timer, DUMMY_INT_KTIME,
HRTIMER_MODE_REL_SOFT);
}

@@ -2391,7 +2400,8 @@ static int dummy_bus_resume(struct usb_h
dum_hcd->rh_state = DUMMY_RH_RUNNING;
set_link_state(dum_hcd);
if (!list_empty(&dum_hcd->urbp_list))
- hrtimer_start(&dum_hcd->timer, ns_to_ktime(0), HRTIMER_MODE_REL_SOFT);
+ hrtimer_start(&dum_hcd->timer, DUMMY_INT_KTIME,
+ HRTIMER_MODE_REL_SOFT);
hcd->state = HC_STATE_RUNNING;
}
spin_unlock_irq(&dum_hcd->dum->lock);