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SubjectRe: [PATCH v2 1/2] pvcalls-front: introduce a per sock_mapping refcount
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On 13/02/18 03:13, Stefano Stabellini wrote:
> Introduce a per sock_mapping refcount, in addition to the existing
> global refcount. Thanks to the sock_mapping refcount, we can safely wait
> for it to be 1 in pvcalls_front_release before freeing an active socket,
> instead of waiting for the global refcount to be 1.
>
> Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
>
> ---
> Changes in v2:
> - fix code style
> - nicer checks in pvcalls_front_release
> - fix check in pvcalls_enter_sock
> ---
> drivers/xen/pvcalls-front.c | 193 +++++++++++++++++++-------------------------
> 1 file changed, 81 insertions(+), 112 deletions(-)
>
> diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> index 4c789e6..163bf8c 100644
> --- a/drivers/xen/pvcalls-front.c
> +++ b/drivers/xen/pvcalls-front.c
> @@ -60,6 +60,7 @@ struct sock_mapping {
> bool active_socket;
> struct list_head list;
> struct socket *sock;
> + atomic_t refcount;
> union {
> struct {
> int irq;
> @@ -93,6 +94,34 @@ struct sock_mapping {
> };
> };
>
> +static inline struct sock_mapping *pvcalls_enter_sock(struct socket *sock)
> +{
> + struct sock_mapping *map = NULL;

Pointless initializer.

> +
> + if (!pvcalls_front_dev ||
> + dev_get_drvdata(&pvcalls_front_dev->dev) == NULL)
> + return ERR_PTR(-ENOTCONN);
> +
> + pvcalls_enter();
> + map = (struct sock_mapping *)sock->sk->sk_send_head;
> + if (map == NULL) {
> + pvcalls_exit()
> + return ERR_PTR(-ENOTSOCK);
> + }

Sorry for noticing this only now: any reason you don't call
pvcalls_enter() only here instead? This would remove the need of
calling pvcalls_exit() if map == NULL.

I can't see pvcalls_enter() protecting sock->sk->sk_send_head in any
way.

> +
> + atomic_inc(&map->refcount);
> + return map;
> +}
> +
> +static inline void pvcalls_exit_sock(struct socket *sock)
> +{
> + struct sock_mapping *map = NULL;

Pointless initializer again.


Juergen

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