linux-kernel - Re: [PATCH v4 02/13] xen/pvcalls: implement frontend disconnect

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Date:   Wed, 20 Sep 2017 16:32:32 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xen.org
Cc:     linux-kernel@...r.kernel.org, jgross@...e.com,
        Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH v4 02/13] xen/pvcalls: implement frontend disconnect


> +
> +struct pvcalls_bedata {
> +	struct xen_pvcalls_front_ring ring;
> +	grant_ref_t ref;
> +	int irq;
> +
> +	struct list_head socket_mappings;
> +	struct list_head socketpass_mappings;
> +	spinlock_t socket_lock;
> +
> +	wait_queue_head_t inflight_req;
> +	struct xen_pvcalls_response rsp[PVCALLS_NR_REQ_PER_RING];
> +};
> +static struct xenbus_device *pvcalls_front_dev;
> +static atomic_t pvcalls_refcount;

Should the refcount be per back/frontend?

> +
> +/* first increment refcount, then proceed */
> +#define pvcalls_enter {                     \
> +	atomic_inc(&pvcalls_refcount);      \
> +	smp_mb();                           \
> +}
> +
> +/* first complete other operations, then decrement refcount */
> +#define pvcalls_exit {                      \
> +	smp_mb();                           \
> +	atomic_dec(&pvcalls_refcount);      \
> +}

I think atomic increment/decrement imply a barrier.


-boris