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

Alan Stern
2024-10-16T00:54:55Z

On Tue, Oct 15, 2024 at 12:54:02PM -0700, syzbot wrote:
> Hello,
>
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:

Arghh... Mistake in the patch caused the debugging info not to be
printed. Here's a corrected version.

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";
@@ -239,6 +239,12 @@ enum dummy_rh_state {
DUMMY_RH_RUNNING
};

+struct alaninfo {
+ const char * str;
+ int starts, stops;
+};
+#define MAX_INFO 16
+
struct dummy_hcd {
struct dummy *dum;
enum dummy_rh_state rh_state;
@@ -257,6 +263,10 @@ struct dummy_hcd {
unsigned active:1;
unsigned old_active:1;
unsigned resuming:1;
+
+ struct alaninfo alaninfo[MAX_INFO];
+ int alanindex;
+ int starts, stops;
};

struct dummy {
@@ -323,6 +333,44 @@ 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, int type);
+void alandbg(struct dummy_hcd *dum_hcd, const char *str, int type)
+{
+ int i = dum_hcd->alanindex;
+ struct alaninfo *info = &dum_hcd->alaninfo[i];
+
+ if (type == 1)
+ ++dum_hcd->starts;
+ else if (type == 2)
+ ++dum_hcd->stops;
+ info->str = str;
+ info->starts = dum_hcd->starts;
+ info->stops = dum_hcd->stops;
+
+ if (++i >= MAX_INFO)
+ i = 0;
+ dum_hcd->alanindex = i;
+}
+
+void alandump(struct dummy_hcd *dum_hcd);
+void alandump(struct dummy_hcd *dum_hcd)
+{
+ int i = dum_hcd->alanindex;
+ int j;
+ struct alaninfo *info = &dum_hcd->alaninfo[i];
+ char *p, buf[4 * 24];
+
+ p = buf;
+ for (j = 0; j < 4; ++j) {
+ if (--i < 0)
+ i = MAX_INFO - 1;
+ info = &dum_hcd->alaninfo[i];
+ p += sprintf(p, "%s %d %d ",
+ info->str, info->starts, info->stops);
+ }
+ dev_info(dummy_dev(dum_hcd), "%s\n", buf);
+}
+
/*-------------------------------------------------------------------------*/

/* DEVICE/GADGET SIDE UTILITY ROUTINES */
@@ -1303,9 +1351,11 @@ 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", 1);
+ hrtimer_start(&dum_hcd->timer, DUMMY_INT_KTIME,
HRTIMER_MODE_REL_SOFT);
+ }

done:
spin_unlock_irqrestore(&dum_hcd->dum->lock, flags);
@@ -1325,9 +1375,17 @@ 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)) {
+ hrtimer_start(&dum_hcd->timer, DUMMY_INT_KTIME,
+ HRTIMER_MODE_REL_SOFT);
+ alandbg(dum_hcd, "start2", 1);
+ } else {
+ int active = hrtimer_active(&dum_hcd->timer);
+ dev_info(dummy_dev(dum_hcd), "Dequeue norestart: %d %d active %d\n",
+ rc, list_empty(&dum_hcd->urbp_list), active);
+ if (rc == 0 && !active)
+ alandump(dum_hcd);
+ }
spin_unlock_irqrestore(&dum_hcd->dum->lock, flags);
return rc;
}
@@ -1813,10 +1871,12 @@ 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", 0);

if (!dum_hcd->udev) {
dev_err(dummy_dev(dum_hcd),
"timer fired with no URBs pending?\n");
+ alandbg(dum_hcd, "handler2", 2);
spin_unlock_irqrestore(&dum->lock, flags);
return HRTIMER_NORESTART;
}
@@ -1994,10 +2054,13 @@ return_urb:
if (list_empty(&dum_hcd->urbp_list)) {
usb_put_dev(dum_hcd->udev);
dum_hcd->udev = NULL;
+ alandbg(dum_hcd, "handler3", 2);
} 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", 1);
+ hrtimer_start(&dum_hcd->timer, DUMMY_INT_KTIME,
HRTIMER_MODE_REL_SOFT);
+ } else {
+ alandbg(dum_hcd, "handler4", 2);
}

spin_unlock_irqrestore(&dum->lock, flags);
@@ -2390,8 +2453,11 @@ 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", 1);
+ 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 +2556,10 @@ static int dummy_start(struct usb_hcd *h
{
struct dummy_hcd *dum_hcd = hcd_to_dummy_hcd(hcd);

+ int i;
+ for (i = 0; i < MAX_INFO; ++i)
+ dum_hcd->alaninfo[i].str = "";
+
/*
* 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 +2591,7 @@ static void dummy_stop(struct usb_hcd *h
{
struct dummy_hcd *dum_hcd = hcd_to_dummy_hcd(hcd);

+ alandbg(dum_hcd, "cancel", 0);
hrtimer_cancel(&dum_hcd->timer);
device_remove_file(dummy_dev(dum_hcd), &dev_attr_urbs);
dev_info(dummy_dev(dum_hcd), "stopped\n");