[Xen-devel] [PATCH net-next 2/2] xen-netback: avoid allocating variable size array on stack

[Wei Liu <wei.liu2@xxxxxxxxxx>]

Tune xen_netbk_count_requests to not touch working array beyond limit, so that
we can make working array size constant.

Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 drivers/net/xen-netback/netback.c |   26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/drivers/net/xen-netback/netback.c 
b/drivers/net/xen-netback/netback.c
index c44772d..c6dc084 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -934,11 +934,15 @@ static int netbk_count_requests(struct xenvif *vif,
        RING_IDX cons = vif->tx.req_cons;
        int slots = 0;
        int drop_err = 0;
+       int keep_looping;
 
        if (!(first->flags & XEN_NETTXF_more_data))
                return 0;
 
        do {
+               struct xen_netif_tx_request dropped_tx = { 0 };
+               int cross_page = 0;
+
                if (slots >= work_to_do) {
                        netdev_err(vif->dev,
                                   "Asked for %d slots but exceeds this 
limit\n",
@@ -972,8 +976,12 @@ static int netbk_count_requests(struct xenvif *vif,
                        drop_err = -E2BIG;
                }
 
-               memcpy(txp, RING_GET_REQUEST(&vif->tx, cons + slots),
-                      sizeof(*txp));
+               if (!drop_err)
+                       memcpy(txp, RING_GET_REQUEST(&vif->tx, cons + slots),
+                              sizeof(*txp));
+               else
+                       memcpy(&dropped_tx, RING_GET_REQUEST(&vif->tx, cons + 
slots),
+                              sizeof(dropped_tx));
 
                /* If the guest submitted a frame >= 64 KiB then
                 * first->size overflowed and following slots will
@@ -995,13 +1003,21 @@ static int netbk_count_requests(struct xenvif *vif,
                first->size -= txp->size;
                slots++;
 
-               if (unlikely((txp->offset + txp->size) > PAGE_SIZE)) {
+               if (!drop_err)
+                       cross_page = (txp->offset + txp->size) > PAGE_SIZE;
+               else
+                       cross_page = (dropped_tx.offset + dropped_tx.size) > 
PAGE_SIZE;
+
+               if (unlikely(cross_page)) {
                        netdev_err(vif->dev, "Cross page boundary, txp->offset: 
%x, size: %u\n",
                                 txp->offset, txp->size);
                        netbk_fatal_tx_err(vif);
                        return -EINVAL;
                }
-       } while ((txp++)->flags & XEN_NETTXF_more_data);
+
+               keep_looping = (!drop_err && (txp++)->flags & 
XEN_NETTXF_more_data) ||
+                       (dropped_tx.flags & XEN_NETTXF_more_data);
+       } while (keep_looping);
 
        if (drop_err) {
                netbk_tx_err(vif, first, cons + slots);
@@ -1408,7 +1424,7 @@ static unsigned xen_netbk_tx_build_gops(struct xen_netbk 
*netbk)
                !list_empty(&netbk->net_schedule_list)) {
                struct xenvif *vif;
                struct xen_netif_tx_request txreq;
-               struct xen_netif_tx_request txfrags[max_skb_slots];
+               struct xen_netif_tx_request txfrags[XEN_NETIF_NR_SLOTS_MIN];
                struct page *page;
                struct xen_netif_extra_info extras[XEN_NETIF_EXTRA_TYPE_MAX-1];
                u16 pending_idx;
-- 
1.7.10.4


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