linux-kernel - Re: INFO: rcu detected stall in dummy

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Date:   Mon, 16 Sep 2019 15:53:05 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     syzbot <syzbot+b24d736f18a1541ad550@...kaller.appspotmail.com>
cc:     andreyknvl@...gle.com, <balbi@...nel.org>,
        <chunfeng.yun@...iatek.com>, <gregkh@...uxfoundation.org>,
        <linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        <syzkaller-bugs@...glegroups.com>
Subject: Re: INFO: rcu detected stall in dummy_timer

On Fri, 13 Sep 2019, syzbot wrote:

> syzbot has found a reproducer for the following crash on:
> 
> HEAD commit:    f0df5c1b usb-fuzzer: main usb gadget fuzzer driver
> git tree:       https://github.com/google/kasan.git usb-fuzzer
> console output: https://syzkaller.appspot.com/x/log.txt?x=1146550d600000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5c6633fa4ed00be5
> dashboard link: https://syzkaller.appspot.com/bug?extid=b24d736f18a1541ad550
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11203fa5600000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=162cd335600000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+b24d736f18a1541ad550@...kaller.appspotmail.com
> 
> yurex 3-1:0.101: yurex_interrupt - unknown status received: -71
> yurex 5-1:0.101: yurex_interrupt - unknown status received: -71
> yurex 6-1:0.101: yurex_interrupt - unknown status received: -71

Let's see if preventing blind resubmissions fixes the problem.

Alan Stern

#syz test: https://github.com/google/kasan.git f0df5c1b

 drivers/usb/misc/yurex.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Index: usb-devel/drivers/usb/misc/yurex.c
===================================================================
--- usb-devel.orig/drivers/usb/misc/yurex.c
+++ usb-devel/drivers/usb/misc/yurex.c
@@ -132,6 +132,7 @@ static void yurex_interrupt(struct urb *
 	switch (status) {
 	case 0: /*success*/
 		break;
+	/* The device is terminated or messed up, give up */
 	case -EOVERFLOW:
 		dev_err(&dev->interface->dev,
 			"%s - overflow with length %d, actual length is %d\n",
@@ -140,12 +141,12 @@ static void yurex_interrupt(struct urb *
 	case -ENOENT:
 	case -ESHUTDOWN:
 	case -EILSEQ:
-		/* The device is terminated, clean up */
+	case -EPROTO:
 		return;
 	default:
 		dev_err(&dev->interface->dev,
 			"%s - unknown status received: %d\n", __func__, status);
-		goto exit;
+		return;
 	}
 
 	/* handle received message */
@@ -177,7 +178,6 @@ static void yurex_interrupt(struct urb *
 		break;
 	}
 
-exit:
 	retval = usb_submit_urb(dev->urb, GFP_ATOMIC);
 	if (retval) {
 		dev_err(&dev->interface->dev, "%s - usb_submit_urb failed: %d\n",