Re: [syzbot] [fs?] [usb?] INFO: rcu detected stall in vfs_readlink

[Oliver Neukum]

On 22.05.23 15:01, Christian Brauner wrote:
> On Fri, May 19, 2023 at 08:18:45PM -0700, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    a4422ff22142 usb: typec: qcom: Add Qualcomm PMIC Type-C dr..
> > 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=10ce218e280000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=2414a945e4542ec1
> > dashboard link: https://syzkaller.appspot.com/bug?extid=24d1639a31b024b125bd
> > compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=137d4c06280000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17b758a1280000
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/414817142fb7/disk-a4422ff2.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/448dba0d344e/vmlinux-a4422ff2.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/d0ad9fe848e2/bzImage-a4422ff2.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+24d1639a31b024b125bd@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > imon 1-1:0.0: imon usb_rx_callback_intf0: status(-71): ignored
> > imon 5-1:0.0: imon usb_rx_callback_intf0: status(-71): ignored
>
> I have the strong suspicion that the usb drive is removed or some such
> nonsense. Doesn't seem an fs bug.


It hasn't been removed. On a real system it would likely be.
The device keeps returning only -EPROTO. As we are dealing with virtual
hardware that is fast enough to cause a livelock from the error
handling retrying the IO without delay.

Handling this nicely would need a real error handler with a workqueue
and some delays and evetually more drastic action like resetting the
device.

	Regards
		Oliver