linux-kernel - Re: [PATCH v3 1/2] usbip: give back URBs for unsent unlink requests during cleanup

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Date:   Thu, 19 Aug 2021 23:39:05 +0530
From:   Anirudh Rayabharam <mail@...rudhrb.com>
To:     Shuah Khan <skhan@...uxfoundation.org>
Cc:     Greg KH <gregkh@...uxfoundation.org>, valentina.manea.m@...il.com,
        shuah@...nel.org,
        syzbot+74d6ef051d3d2eacf428@...kaller.appspotmail.com,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] usbip: give back URBs for unsent unlink requests
 during cleanup

On Wed, Aug 18, 2021 at 12:36:11PM -0600, Shuah Khan wrote:
> On 8/17/21 11:39 PM, Greg KH wrote:
> > On Tue, Aug 17, 2021 at 05:16:51PM -0600, Shuah Khan wrote:
> > > On 8/13/21 12:25 PM, Anirudh Rayabharam wrote:
> > > > In vhci_device_unlink_cleanup(), the URBs for unsent unlink requests are
> > > > not given back. This sometimes causes usb_kill_urb to wait indefinitely
> > > > for that urb to be given back. syzbot has reported a hung task issue [1]
> > > > for this.
> > > > 
> > > > To fix this, give back the urbs corresponding to unsent unlink requests
> > > > (unlink_tx list) similar to how urbs corresponding to unanswered unlink
> > > > requests (unlink_rx list) are given back.
> > > > 
> > > > [1]: https://syzkaller.appspot.com/bug?id=08f12df95ae7da69814e64eb5515d5a85ed06b76
> > > > 
> > > > Reported-by: syzbot+74d6ef051d3d2eacf428@...kaller.appspotmail.com
> > > > Tested-by: syzbot+74d6ef051d3d2eacf428@...kaller.appspotmail.com
> > > > Signed-off-by: Anirudh Rayabharam <mail@...rudhrb.com>
> > > > ---
> > > >    drivers/usb/usbip/vhci_hcd.c | 26 ++++++++++++++++++++++++++
> > > >    1 file changed, 26 insertions(+)
> > > > 
> > > > diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
> > > > index 4ba6bcdaa8e9..6f3f374d4bbc 100644
> > > > --- a/drivers/usb/usbip/vhci_hcd.c
> > > > +++ b/drivers/usb/usbip/vhci_hcd.c
> > > > @@ -957,8 +957,34 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
> > > >    	spin_lock(&vdev->priv_lock);
> > > >    	list_for_each_entry_safe(unlink, tmp, &vdev->unlink_tx, list) {
> > > > +		struct urb *urb;
> > > > +
> > > > +		/* give back URB of unsent unlink request */
> > > >    		pr_info("unlink cleanup tx %lu\n", unlink->unlink_seqnum);
> > > 
> > > I know this is an exiting one.
> > > Let's make this pr_debug or remove it all together.
> > > 
> > > > +
> > > > +		urb = pickup_urb_and_free_priv(vdev, unlink->unlink_seqnum);
> > > > +		if (!urb) {
> > > > +			pr_info("the urb (seqnum %lu) was already given back\n",
> > > > +				unlink->unlink_seqnum);
> > > 
> > > Let's make this pr_debug or remove it all together.
> > 
> > As you have a struct device for all of these, please use dev_dbg() and
> > friends, not pr_*(), for all of these.
> > 
> 
> Yes. Makes perfect sense.

Perhaps we should use usbip_dbg_vhci_hc() instead of dev_dbg()? It is
one of the custom macros defined by the usbip driver for printing debug
logs.

Thanks,

	Anirudh