linux-kernel - Re: [syzbot] [usb?] INFO: rcu detected stall in raw

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Message-ID: <e8b8013b-d8b4-4eee-8643-1d512aa17133@rowland.harvard.edu>
Date: Mon, 10 Jun 2024 13:24:50 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: syzbot <syzbot+5f996b83575ef4058638@...kaller.appspotmail.com>
Cc: gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
  linux-usb@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [usb?] INFO: rcu detected stall in raw_ioctl

On Sat, Jun 08, 2024 at 09:41:04PM -0700, syzbot wrote:
> Hello,
> 
> syzbot has tested the proposed patch and the reproducer did not trigger any issue:
> 
> Reported-and-tested-by: syzbot+5f996b83575ef4058638@...kaller.appspotmail.com
> 
> Tested on:
> 
> commit:         8867bbd4 mm: arm64: Fix the out-of-bounds issue in con..
> git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
> console output: https://syzkaller.appspot.com/x/log.txt?x=11f0680a980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=3b4350cf56c61c80
> dashboard link: https://syzkaller.appspot.com/bug?extid=5f996b83575ef4058638
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> userspace arch: arm64
> patch:          https://syzkaller.appspot.com/x/patch.diff?x=118743fc980000
> 
> Note: testing is done by a robot and is best-effort only.

I'd like to determine the reason behind this entire class of bugs.  As 
far as I can see, the design of dummy-hcd shouldn't allow them to occur.

Alan Stern

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git 8867bbd4a056

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
@@ -1826,6 +1826,7 @@ static void dummy_timer(struct timer_lis
 			break;
 		dum->ep[i].already_seen = 0;
 	}
+	dev_info(dummy_dev(dum_hcd), "Timer handler\n");
 
 restart:
 	list_for_each_entry_safe(urbp, tmp, &dum_hcd->urbp_list, urbp_list) {
@@ -1835,6 +1836,9 @@ restart:
 		struct dummy_ep		*ep = NULL;
 		int			status = -EINPROGRESS;
 
+		dev_info(dummy_dev(dum_hcd), "urbp %p %x next_frame %p\n",
+				urbp, urbp->urb->pipe, dum_hcd->next_frame_urbp);
+
 		/* stop when we reach URBs queued after the timer interrupt */
 		if (urbp == dum_hcd->next_frame_urbp)
 			break;