From: Shuah Khan <skhan@linuxfoundation.org>
To: Anirudh Rayabharam <mail@anirudhrb.com>,
Valentina Manea <valentina.manea.m@gmail.com>,
Shuah Khan <shuah@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-kernel@vger.kernel.org,
linux-kernel-mentees@lists.linuxfoundation.org,
linux-usb@vger.kernel.org,
syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com,
Shuah Khan <skhan@linuxfoundation.org>
Subject: Re: [PATCH v2] usbip: give back URBs for unsent unlink requests during cleanup
Date: Tue, 10 Aug 2021 17:25:51 -0600 [thread overview]
Message-ID: <4aaf420d-e85e-212e-3bc4-a70e016de610@linuxfoundation.org> (raw)
In-Reply-To: <20210806181335.2078-1-mail@anirudhrb.com>
On 8/6/21 12:13 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. Since the code is almost the
> same, extract it into a new function and call it for both unlink_rx and
> unlink_tx lists.
>
Let's not do the refactor - let's first fix the problem and then the refactor.
> [1]: https://syzkaller.appspot.com/bug?id=08f12df95ae7da69814e64eb5515d5a85ed06b76
>
> Reported-by: syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com
> Tested-by: syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com
> Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
> ---
>
> Changes in v2:
> Use WARN_ON() instead of BUG() when unlink_list is neither unlink_tx nor
> unlink_rx.
>
> v1: https://lore.kernel.org/lkml/20210806164015.25263-1-mail@anirudhrb.com/
>
> ---
> drivers/usb/usbip/vhci_hcd.c | 45 +++++++++++++++++++++++++-----------
> 1 file changed, 32 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
> index 4ba6bcdaa8e9..67e638f4c455 100644
> --- a/drivers/usb/usbip/vhci_hcd.c
> +++ b/drivers/usb/usbip/vhci_hcd.c
> @@ -945,7 +945,8 @@ static int vhci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
> return 0;
> }
>
> -static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
> +static void __vhci_cleanup_unlink_list(struct vhci_device *vdev,
> + struct list_head *unlink_list)
> {
> struct vhci_hcd *vhci_hcd = vdev_to_vhci_hcd(vdev);
> struct usb_hcd *hcd = vhci_hcd_to_hcd(vhci_hcd);
> @@ -953,23 +954,23 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
> struct vhci_unlink *unlink, *tmp;
> unsigned long flags;
>
> + if (WARN(unlink_list != &vdev->unlink_tx
> + && unlink_list != &vdev->unlink_rx,
> + "Invalid list passed to __vhci_cleanup_unlink_list\n"))
> + return;
> +
With this change, this will be only place unlink_rx is used without
vdev->priv_lock hold? Please explain why this is safe.
> spin_lock_irqsave(&vhci->lock, flags);
> spin_lock(&vdev->priv_lock);
>
> - list_for_each_entry_safe(unlink, tmp, &vdev->unlink_tx, list) {
> - pr_info("unlink cleanup tx %lu\n", unlink->unlink_seqnum);
> - list_del(&unlink->list);
> - kfree(unlink);
> - }
> -
> - while (!list_empty(&vdev->unlink_rx)) {
> + list_for_each_entry_safe(unlink, tmp, unlink_list, list) {
> struct urb *urb;
>
> - unlink = list_first_entry(&vdev->unlink_rx, struct vhci_unlink,
> - list);
> -
> - /* give back URB of unanswered unlink request */
> - pr_info("unlink cleanup rx %lu\n", unlink->unlink_seqnum);
> + if (unlink_list == &vdev->unlink_tx)
> + pr_info("unlink cleanup tx %lu\n",
> + unlink->unlink_seqnum);
> + else
> + pr_info("unlink cleanup rx %lu\n",
> + unlink->unlink_seqnum);
>
> urb = pickup_urb_and_free_priv(vdev, unlink->unlink_seqnum);
> if (!urb) {
> @@ -1001,6 +1002,24 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
> spin_unlock_irqrestore(&vhci->lock, flags);
> }
>
> +static inline void vhci_cleanup_unlink_tx(struct vhci_device *vdev)
> +{
> + __vhci_cleanup_unlink_list(vdev, &vdev->unlink_tx);
With this change, this will be only place unlink_rx is used without
vdev->priv_lock hold? Please explain why this is safe.
> +}
> +
Is there a need for this layer?
> +static inline void vhci_cleanup_unlink_rx(struct vhci_device *vdev)
> +{
> + __vhci_cleanup_unlink_list(vdev, &vdev->unlink_rx);
With this change, this will be only place unlink_rx is used without
vdev->priv_lock hold? Please explain why this is safe.
> +}
> +
Is there a need for this layer?
> +static void vhci_device_unlink_cleanup(struct vhci_device *vdev)
> +{
> + /* give back URBs of unsent unlink requests */
> + vhci_cleanup_unlink_tx(vdev);
> + /* give back URBs of unanswered unlink requests */
> + vhci_cleanup_unlink_rx(vdev);
> +}
> +
> /*
> * The important thing is that only one context begins cleanup.
> * This is why error handling and cleanup become simple.
>
thanks,
-- Shuah
next prev parent reply other threads:[~2021-08-10 23:25 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-06 18:13 [PATCH v2] usbip: give back URBs for unsent unlink requests during cleanup Anirudh Rayabharam
2021-08-10 23:25 ` Shuah Khan [this message]
2021-08-11 13:58 ` Anirudh Rayabharam
2021-08-11 21:51 ` Shuah Khan
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