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

Alan Stern
2024-10-15T14:22:52Z

On Mon, Oct 14, 2024 at 11:42:02AM -0700, syzbot wrote:
> Hello,
>
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:

Let's try to get some more debugging info.

Alan Stern

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git v6.12-rc3

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";
@@ -257,6 +257,9 @@ struct dummy_hcd {
unsigned active:1;
unsigned old_active:1;
unsigned resuming:1;
+
+ int alanflag;
+ const char *alanstr;
};

struct dummy {
@@ -323,6 +326,14 @@ static inline struct dummy *gadget_dev_t
return container_of(dev, struct dummy, gadget.dev);
}

+void alandbg(struct dummy_hcd *dum_hcd, const char *str);
+void alandbg(struct dummy_hcd *dum_hcd, const char *str)
+{
+ dum_hcd->alanstr = str;
+ if (dum_hcd->alanflag)
+ dev_info(dummy_dev(dum_hcd), str);
+}
+
/*-------------------------------------------------------------------------*/

/* DEVICE/GADGET SIDE UTILITY ROUTINES */
@@ -1303,9 +1314,11 @@ static int dummy_urb_enqueue(
urb->error_count = 1; /* mark as a new 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),
+ if (!hrtimer_active(&dum_hcd->timer)) {
+ alandbg(dum_hcd, "start1");
+ hrtimer_start(&dum_hcd->timer, DUMMY_INT_KTIME,
HRTIMER_MODE_REL_SOFT);
+ }

done:
spin_unlock_irqrestore(&dum_hcd->dum->lock, flags);
@@ -1325,9 +1338,19 @@ 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)) {
+ dev_info(dummy_dev(dum_hcd), "Dequeue restart %p\n", urb);
+ hrtimer_start(&dum_hcd->timer, DUMMY_INT_KTIME,
+ HRTIMER_MODE_REL_SOFT);
+ alandbg(dum_hcd, "start2");
+ } else {
+ dev_info(dummy_dev(dum_hcd), "Dequeue norestart: %d %d %d %p active %d %s\n",
+ rc, dum_hcd->rh_state,
+ list_empty(&dum_hcd->urbp_list), urb,
+ hrtimer_active(&dum_hcd->timer),
+ dum_hcd->alanstr);
+ }
+ ++dum_hcd->alanflag;
spin_unlock_irqrestore(&dum_hcd->dum->lock, flags);
return rc;
}
@@ -1813,10 +1836,12 @@ static enum hrtimer_restart dummy_timer(

/* look at each urb queued by the host side driver */
spin_lock_irqsave(&dum->lock, flags);
+ alandbg(dum_hcd, "handler1");

if (!dum_hcd->udev) {
dev_err(dummy_dev(dum_hcd),
"timer fired with no URBs pending?\n");
+ alandbg(dum_hcd, "handler2");
spin_unlock_irqrestore(&dum->lock, flags);
return HRTIMER_NORESTART;
}
@@ -1984,6 +2009,8 @@ return_urb:
ep->already_seen = ep->setup_stage = 0;

usb_hcd_unlink_urb_from_ep(dummy_hcd_to_hcd(dum_hcd), urb);
+ if (dum_hcd->alanflag)
+ 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);
@@ -1994,12 +2021,17 @@ return_urb:
if (list_empty(&dum_hcd->urbp_list)) {
usb_put_dev(dum_hcd->udev);
dum_hcd->udev = NULL;
+ alandbg(dum_hcd, "handler3");
} 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),
+ alandbg(dum_hcd, "handler-start");
+ hrtimer_start(&dum_hcd->timer, DUMMY_INT_KTIME,
HRTIMER_MODE_REL_SOFT);
+ } else {
+ alandbg(dum_hcd, "handler4");
}

+ if (dum_hcd->alanflag > 0)
+ --dum_hcd->alanflag;
spin_unlock_irqrestore(&dum->lock, flags);

return HRTIMER_NORESTART;
@@ -2390,8 +2422,11 @@ static int dummy_bus_resume(struct usb_h
} else {
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);
+ if (!list_empty(&dum_hcd->urbp_list)) {
+ alandbg(dum_hcd, "start3");
+ hrtimer_start(&dum_hcd->timer, DUMMY_INT_KTIME,
+ HRTIMER_MODE_REL_SOFT);
+ }
hcd->state = HC_STATE_RUNNING;
}
spin_unlock_irq(&dum_hcd->dum->lock);
@@ -2490,6 +2525,7 @@ static int dummy_start(struct usb_hcd *h
{
struct dummy_hcd *dum_hcd = hcd_to_dummy_hcd(hcd);

+ dum_hcd->alanstr = "init";
/*
* HOST side init ... we emulate a root hub that'll only ever
* talk to one device (the gadget side). Also appears in sysfs,
@@ -2521,6 +2557,7 @@ static void dummy_stop(struct usb_hcd *h
{
struct dummy_hcd *dum_hcd = hcd_to_dummy_hcd(hcd);

+ alandbg(dum_hcd, "cancel");
hrtimer_cancel(&dum_hcd->timer);
device_remove_file(dummy_dev(dum_hcd), &dev_attr_urbs);
dev_info(dummy_dev(dum_hcd), "stopped\n");