[PATCH 4.4 31/52] xen/netfront: disentangle tx_skb_freelist

Greg Kroah-Hartman
2021-12-06T15:00:57Z

From: Juergen Gross <jgross@suse.com>

commit 21631d2d741a64a073e167c27769e73bc7844a2f upstream.

The tx_skb_freelist elements are in a single linked list with the
request id used as link reference. The per element link field is in a
union with the skb pointer of an in use request.

Move the link reference out of the union in order to enable a later
reuse of it for requests which need a populated skb pointer.

Rename add_id_to_freelist() and get_id_from_freelist() to
add_id_to_list() and get_id_from_list() in order to prepare using
those for other lists as well. Define ~0 as value to indicate the end
of a list and place that value into the link for a request not being
on the list.

When freeing a skb zero the skb pointer in the request. Use a NULL
value of the skb pointer instead of skb_entry_is_link() for deciding
whether a request has a skb linked to it.

Remove skb_entry_set_link() and open code it instead as it is really
trivial now.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/xen-netfront.c | 61 ++++++++++++++++++---------------------------
1 file changed, 25 insertions(+), 36 deletions(-)

--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -120,17 +120,11 @@ struct netfront_queue {

/*
* {tx,rx}_skbs store outstanding skbuffs. Free tx_skb entries
- * are linked from tx_skb_freelist through skb_entry.link.
- *
- * NB. Freelist index entries are always going to be less than
- * PAGE_OFFSET, whereas pointers to skbs will always be equal or
- * greater than PAGE_OFFSET: we use this property to distinguish
- * them.
+ * are linked from tx_skb_freelist through tx_link.
*/
- union skb_entry {
- struct sk_buff *skb;
- unsigned long link;
- } tx_skbs[NET_TX_RING_SIZE];
+ struct sk_buff *tx_skbs[NET_TX_RING_SIZE];
+ unsigned short tx_link[NET_TX_RING_SIZE];
+#define TX_LINK_NONE 0xffff
grant_ref_t gref_tx_head;
grant_ref_t grant_tx_ref[NET_TX_RING_SIZE];
struct page *grant_tx_page[NET_TX_RING_SIZE];
@@ -168,33 +162,25 @@ struct netfront_rx_info {
struct xen_netif_extra_info extras[XEN_NETIF_EXTRA_TYPE_MAX - 1];
};

-static void skb_entry_set_link(union skb_entry *list, unsigned short id)
-{
- list->link = id;
-}
-
-static int skb_entry_is_link(const union skb_entry *list)
-{
- BUILD_BUG_ON(sizeof(list->skb) != sizeof(list->link));
- return (unsigned long)list->skb < PAGE_OFFSET;
-}
-
/*
* Access macros for acquiring freeing slots in tx_skbs[].
*/

-static void add_id_to_freelist(unsigned *head, union skb_entry *list,
- unsigned short id)
+static void add_id_to_list(unsigned *head, unsigned short *list,
+ unsigned short id)
{
- skb_entry_set_link(&list[id], *head);
+ list[id] = *head;
*head = id;
}

-static unsigned short get_id_from_freelist(unsigned *head,
- union skb_entry *list)
+static unsigned short get_id_from_list(unsigned *head, unsigned short *list)
{
unsigned int id = *head;
- *head = list[id].link;
+
+ if (id != TX_LINK_NONE) {
+ *head = list[id];
+ list[id] = TX_LINK_NONE;
+ }
return id;
}

@@ -394,7 +380,8 @@ static void xennet_tx_buf_gc(struct netf
continue;

id = txrsp.id;
- skb = queue->tx_skbs[id].skb;
+ skb = queue->tx_skbs[id];
+ queue->tx_skbs[id] = NULL;
if (unlikely(gnttab_query_foreign_access(
queue->grant_tx_ref[id]) != 0)) {
pr_alert("%s: warning -- grant still in use by backend domain\n",
@@ -407,7 +394,7 @@ static void xennet_tx_buf_gc(struct netf
&queue->gref_tx_head, queue->grant_tx_ref[id]);
queue->grant_tx_ref[id] = GRANT_INVALID_REF;
queue->grant_tx_page[id] = NULL;
- add_id_to_freelist(&queue->tx_skb_freelist, queue->tx_skbs, id);
+ add_id_to_list(&queue->tx_skb_freelist, queue->tx_link, id);
dev_kfree_skb_irq(skb);
}

@@ -450,7 +437,7 @@ static void xennet_tx_setup_grant(unsign
struct netfront_queue *queue = info->queue;
struct sk_buff *skb = info->skb;

- id = get_id_from_freelist(&queue->tx_skb_freelist, queue->tx_skbs);
+ id = get_id_from_list(&queue->tx_skb_freelist, queue->tx_link);
tx = RING_GET_REQUEST(&queue->tx, queue->tx.req_prod_pvt++);
ref = gnttab_claim_grant_reference(&queue->gref_tx_head);
WARN_ON_ONCE(IS_ERR_VALUE((unsigned long)(int)ref));
@@ -458,7 +445,7 @@ static void xennet_tx_setup_grant(unsign
gnttab_grant_foreign_access_ref(ref, queue->info->xbdev->otherend_id,
gfn, GNTMAP_readonly);

- queue->tx_skbs[id].skb = skb;
+ queue->tx_skbs[id] = skb;
queue->grant_tx_page[id] = page;
queue->grant_tx_ref[id] = ref;

@@ -1126,17 +1113,18 @@ static void xennet_release_tx_bufs(struc

for (i = 0; i < NET_TX_RING_SIZE; i++) {
/* Skip over entries which are actually freelist references */
- if (skb_entry_is_link(&queue->tx_skbs[i]))
+ if (!queue->tx_skbs[i])
continue;

- skb = queue->tx_skbs[i].skb;
+ skb = queue->tx_skbs[i];
+ queue->tx_skbs[i] = NULL;
get_page(queue->grant_tx_page[i]);
gnttab_end_foreign_access(queue->grant_tx_ref[i],
GNTMAP_readonly,
(unsigned long)page_address(queue->grant_tx_page[i]));
queue->grant_tx_page[i] = NULL;
queue->grant_tx_ref[i] = GRANT_INVALID_REF;
- add_id_to_freelist(&queue->tx_skb_freelist, queue->tx_skbs, i);
+ add_id_to_list(&queue->tx_skb_freelist, queue->tx_link, i);
dev_kfree_skb_irq(skb);
}
}
@@ -1637,13 +1625,14 @@ static int xennet_init_queue(struct netf
snprintf(queue->name, sizeof(queue->name), "vif%s-q%u",
devid, queue->id);

- /* Initialise tx_skbs as a free chain containing every entry. */
+ /* Initialise tx_skb_freelist as a free chain containing every entry. */
queue->tx_skb_freelist = 0;
for (i = 0; i < NET_TX_RING_SIZE; i++) {
- skb_entry_set_link(&queue->tx_skbs[i], i+1);
+ queue->tx_link[i] = i + 1;
queue->grant_tx_ref[i] = GRANT_INVALID_REF;
queue->grant_tx_page[i] = NULL;
}
+ queue->tx_link[NET_TX_RING_SIZE - 1] = TX_LINK_NONE;

/* Clear out rx_skbs */
for (i = 0; i < NET_RX_RING_SIZE; i++) {