Re: [PATCH] usbip: vhci_hcd: slighly simplify code in 'vhci_urb_dequeue()'

[Christophe JAILLET]

Le 23/03/2020 Ã 17:48, shuah a ÃcritÂ:
> 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.
No, the issue is just theoretical.


> > Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
> > ---
> > Â drivers/usb/usbip/vhci_hcd.c | 5 ++---
> > Â 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)
> > ÂÂÂÂÂÂÂÂÂ /* tcp connection is alive */
> > ÂÂÂÂÂÂÂÂÂ struct vhci_unlink *unlink;
> > Â -ÂÂÂÂÂÂÂ 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.

My proposal was just a small clean-up (from my point of view at least).
If it can have some side effects, please, just consider it as a NACK.

CJ

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