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

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Message-ID: <c1145389-2695-41d9-ac30-f8819c2ff679@rowland.harvard.edu>
Date: Wed, 16 Oct 2024 10:40:45 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: syzbot <syzbot+f342ea16c9d06d80b585@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [usb?] INFO: task hung in usb_port_suspend

On Tue, Oct 15, 2024 at 07:34:02PM -0700, syzbot wrote:
> Hello,
> 
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:

Okay, the information in the console log confirms it.  The issue is 
definitely caused by the use of hrtimer_active() in dummy_urb_enqueue().  
This patch should be the correct solution.

Alan Stern

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

---
 drivers/usb/gadget/udc/dummy_hcd.c |   20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

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
@@ -254,6 +254,7 @@ struct dummy_hcd {
 	u32				stream_en_ep;
 	u8				num_stream[30 / 2];
 
+	unsigned			timer_pending:1;
 	unsigned			active:1;
 	unsigned			old_active:1;
 	unsigned			resuming:1;
@@ -1303,9 +1304,11 @@ 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))
+	if (!dum_hcd->timer_pending) {
+		dum_hcd->timer_pending = 1;
 		hrtimer_start(&dum_hcd->timer, ns_to_ktime(DUMMY_TIMER_INT_NSECS),
 				HRTIMER_MODE_REL_SOFT);
+	}
 
  done:
 	spin_unlock_irqrestore(&dum_hcd->dum->lock, flags);
@@ -1324,9 +1327,10 @@ static int dummy_urb_dequeue(struct usb_
 	spin_lock_irqsave(&dum_hcd->dum->lock, flags);
 
 	rc = usb_hcd_check_unlink_urb(hcd, urb, status);
-	if (!rc && dum_hcd->rh_state != DUMMY_RH_RUNNING &&
-			!list_empty(&dum_hcd->urbp_list))
+	if (rc == 0 && !dum_hcd->timer_pending) {
+		dum_hcd->timer_pending = 1;
 		hrtimer_start(&dum_hcd->timer, ns_to_ktime(0), HRTIMER_MODE_REL_SOFT);
+	}
 
 	spin_unlock_irqrestore(&dum_hcd->dum->lock, flags);
 	return rc;
@@ -1813,6 +1817,7 @@ static enum hrtimer_restart dummy_timer(
 
 	/* look at each urb queued by the host side driver */
 	spin_lock_irqsave(&dum->lock, flags);
+	dum_hcd->timer_pending = 0;
 
 	if (!dum_hcd->udev) {
 		dev_err(dummy_dev(dum_hcd),
@@ -1994,8 +1999,10 @@ return_urb:
 	if (list_empty(&dum_hcd->urbp_list)) {
 		usb_put_dev(dum_hcd->udev);
 		dum_hcd->udev = NULL;
-	} else if (dum_hcd->rh_state == DUMMY_RH_RUNNING) {
+	} else if (!dum_hcd->timer_pending &&
+			dum_hcd->rh_state == DUMMY_RH_RUNNING) {
 		/* want a 1 msec delay here */
+		dum_hcd->timer_pending = 1;
 		hrtimer_start(&dum_hcd->timer, ns_to_ktime(DUMMY_TIMER_INT_NSECS),
 				HRTIMER_MODE_REL_SOFT);
 	}
@@ -2390,8 +2397,10 @@ 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))
+		if (!list_empty(&dum_hcd->urbp_list)) {
+			dum_hcd->timer_pending = 1;
 			hrtimer_start(&dum_hcd->timer, ns_to_ktime(0), HRTIMER_MODE_REL_SOFT);
+		}
 		hcd->state = HC_STATE_RUNNING;
 	}
 	spin_unlock_irq(&dum_hcd->dum->lock);
@@ -2522,6 +2531,7 @@ static void dummy_stop(struct usb_hcd *h
 	struct dummy_hcd	*dum_hcd = hcd_to_dummy_hcd(hcd);
 
 	hrtimer_cancel(&dum_hcd->timer);
+	dum_hcd->timer_pending = 0;
 	device_remove_file(dummy_dev(dum_hcd), &dev_attr_urbs);
 	dev_info(dummy_dev(dum_hcd), "stopped\n");
 }