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

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Message-ID: <b84d31a3-4353-4506-903a-04f1e1b8cbda@rowland.harvard.edu>
Date: Fri, 11 Oct 2024 20:48:27 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: syzbot <syzbot+f342ea16c9d06d80b585@...kaller.appspotmail.com>
Cc: gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org, sylv@...v.io,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [usb?] INFO: task hung in usb_port_suspend

On Fri, Oct 11, 2024 at 08:45:03AM -0700, syzbot wrote:
> Hello,
> 
> syzbot has tested the proposed patch and the reproducer did not trigger any issue:
> 
> Reported-by: syzbot+f342ea16c9d06d80b585@...kaller.appspotmail.com
> Tested-by: syzbot+f342ea16c9d06d80b585@...kaller.appspotmail.com
> 
> Tested on:
> 
> commit:         4a9fe2a8 dt-bindings: usb: dwc3-imx8mp: add compatible..
> git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing
> console output: https://syzkaller.appspot.com/x/log.txt?x=15346f07980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4510af5d637450fb
> dashboard link: https://syzkaller.appspot.com/bug?extid=f342ea16c9d06d80b585
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> patch:          https://syzkaller.appspot.com/x/patch.diff?x=1456db27980000
> 
> Note: testing is done by a robot and is best-effort only.

Maybe the problem occurs because the hrtimer subsystem doesn't like 
timeouts set to the current moment.  Let's try changing them all to be 
in the future.

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";
@@ -1304,7 +1304,7 @@ static int dummy_urb_enqueue(
 
 	/* 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:
@@ -1326,7 +1326,8 @@ 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);
+		hrtimer_start(&dum_hcd->timer, DUMMY_INT_KTIME,
+				HRTIMER_MODE_REL_SOFT);
 
 	spin_unlock_irqrestore(&dum_hcd->dum->lock, flags);
 	return rc;
@@ -1995,8 +1996,7 @@ 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 +2391,8 @@ 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);