| Message ID | 20200321152938.19580-1-christophe.jaillet@wanadoo.fr (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | usbip: vhci_hcd: slighly simplify code in 'vhci_urb_dequeue()' | expand |
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
Le 23/03/2020 à 17:48, shuah a écrit : > 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@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. 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 > >> /* 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 >
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); - /* 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");
The allocation of 'unlink' can be moved before a spin_lock. This slighly simplifies the error handling if the memory allocation fails, aligns the code structure with what is done in 'vhci_tx_urb()' and reduces potential lock contention. Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> --- drivers/usb/usbip/vhci_hcd.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)