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

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Date:   Tue, 17 Aug 2021 17:16:51 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Anirudh Rayabharam <mail@...rudhrb.com>,
        valentina.manea.m@...il.com, shuah@...nel.org,
        gregkh@...uxfoundation.org
Cc:     syzbot+74d6ef051d3d2eacf428@...kaller.appspotmail.com,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v3 1/2] usbip: give back URBs for unsent unlink requests
 during cleanup

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.

> +			list_del(&unlink->list);
> +			kfree(unlink);
> +			continue;
> +		}
> +
> +		urb->status = -ENODEV;
> +
> +		usb_hcd_unlink_urb_from_ep(hcd, urb);
> +
>   		list_del(&unlink->list);
> +
> +		spin_unlock(&vdev->priv_lock);
> +		spin_unlock_irqrestore(&vhci->lock, flags);
> +
> +		usb_hcd_giveback_urb(hcd, urb, urb->status);
> +
> +		spin_lock_irqsave(&vhci->lock, flags);
> +		spin_lock(&vdev->priv_lock);
> +
>   		kfree(unlink);
>   	}
>   
> 

thanks,
-- Shuah