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SubjectRe: [PATCH] usbip: vhci_hcd: slighly simplify code in 'vhci_urb_dequeue()'
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On 3/21/20 9:29 AM, Christophe JAILLET wrote:
> The allocation of 'unlink' can be moved before a spin_lock.
> This slighly simplifies the error handling if the memory allocation fails,

slightly (spelling nit)

> aligns the code structure with what is done in 'vhci_tx_urb()' and reduces
> potential lock contention.
>

Are you seeing any problems or is this a potential lock contention?
If you are seeing issues, please share the problem seen.


> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> ---
> drivers/usb/usbip/vhci_hcd.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
> index 65850e9c7190..b909a634260c 100644
> --- a/drivers/usb/usbip/vhci_hcd.c
> +++ b/drivers/usb/usbip/vhci_hcd.c
> @@ -905,17 +905,16 @@ static int vhci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
> /* tcp connection is alive */
> struct vhci_unlink *unlink;
>
> - spin_lock(&vdev->priv_lock);
> -

This change might simplify the error path, however it could
open a race window with the unlink activity during
vhci_shutdown_connection() when the connection is being taken
down. It would be safer to hold both locks as soon as the
connection check is done.

> /* setup CMD_UNLINK pdu */
> unlink = kzalloc(sizeof(struct vhci_unlink), GFP_ATOMIC);
> if (!unlink) {
> - spin_unlock(&vdev->priv_lock);
> spin_unlock_irqrestore(&vhci->lock, flags);
> usbip_event_add(&vdev->ud, VDEV_EVENT_ERROR_MALLOC);
> return -ENOMEM;
> }
>
> + spin_lock(&vdev->priv_lock);
> +
> unlink->seqnum = atomic_inc_return(&vhci_hcd->seqnum);
> if (unlink->seqnum == 0xffff)
> pr_info("seqnum max\n");
>

thanks,
-- Shuah

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