linux-kernel - Re: [syzbot] [usb?] INFO: task hung in usb_port

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Message-ID: <f1a79484-2ee0-4160-a2f0-dbfa7b90eece@rowland.harvard.edu>
Date: Mon, 14 Oct 2024 12:14:43 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: syzbot <syzbot+f342ea16c9d06d80b585@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [usb?] INFO: task hung in usb_port_suspend

On Sun, Oct 13, 2024 at 06:58:02PM -0700, syzbot wrote:
> Hello,
> 
> syzbot has tested the proposed patch and the reproducer did not trigger any issue:

It seems that the problem occurs when the timer isn't active in spite of 
the fact that the root hub is running and there are URBs queued.  But 
this shouldn't happen; I need to find the reason why it does and not 
just work around it.

First make sure that it really is the cause.

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";
@@ -257,6 +257,8 @@ struct dummy_hcd {
 	unsigned			active:1;
 	unsigned			old_active:1;
 	unsigned			resuming:1;
+
+	bool				alanflag;
 };
 
 struct dummy {
@@ -1301,10 +1303,12 @@ 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 */
+	dev_info(dummy_dev(dum_hcd), "Enqueue %p type %d\n", urb,
+		usb_pipetype(urb->pipe));
 
 	/* 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 +1329,15 @@ 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)) {
+		dev_info(dummy_dev(dum_hcd), "Dequeue restart %p\n", urb);
+		hrtimer_start(&dum_hcd->timer, DUMMY_INT_KTIME,
+				HRTIMER_MODE_REL_SOFT);
+	} else {
+		dev_info(dummy_dev(dum_hcd), "Dequeue norestart: %d %p active %d\n",
+				rc, urb, hrtimer_active(&dum_hcd->timer));
+	}
+	dum_hcd->alanflag = true;
 	spin_unlock_irqrestore(&dum_hcd->dum->lock, flags);
 	return rc;
 }
@@ -1813,6 +1823,10 @@ static enum hrtimer_restart dummy_timer(
 
 	/* look at each urb queued by the host side driver */
 	spin_lock_irqsave(&dum->lock, flags);
+	if (dum_hcd->alanflag) {
+		dum_hcd->alanflag = false;
+		dev_info(dummy_dev(dum_hcd), "Timer handler\n");
+	}
 
 	if (!dum_hcd->udev) {
 		dev_err(dummy_dev(dum_hcd),
@@ -1984,6 +1998,7 @@ return_urb:
 			ep->already_seen = ep->setup_stage = 0;
 
 		usb_hcd_unlink_urb_from_ep(dummy_hcd_to_hcd(dum_hcd), urb);
+		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 +2010,7 @@ 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 +2405,8 @@ 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);