[Xen-devel] [PATCH net-next V2 2/3] 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.

Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 drivers/net/xen-netback/netback.c |   16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/net/xen-netback/netback.c 
b/drivers/net/xen-netback/netback.c
index c44772d..ce8109f 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -934,11 +934,14 @@ static int netbk_count_requests(struct xenvif *vif,
        RING_IDX cons = vif->tx.req_cons;
        int slots = 0;
        int drop_err = 0;
+       int more_data;
 
        if (!(first->flags & XEN_NETTXF_more_data))
                return 0;
 
        do {
+               struct xen_netif_tx_request dropped_tx = { 0 };
+
                if (slots >= work_to_do) {
                        netdev_err(vif->dev,
                                   "Asked for %d slots but exceeds this 
limit\n",
@@ -972,6 +975,9 @@ static int netbk_count_requests(struct xenvif *vif,
                        drop_err = -E2BIG;
                }
 
+               if (drop_err)
+                       txp = &dropped_tx;
+
                memcpy(txp, RING_GET_REQUEST(&vif->tx, cons + slots),
                       sizeof(*txp));
 
@@ -1001,7 +1007,13 @@ static int netbk_count_requests(struct xenvif *vif,
                        netbk_fatal_tx_err(vif);
                        return -EINVAL;
                }
-       } while ((txp++)->flags & XEN_NETTXF_more_data);
+
+               more_data = txp->flags & XEN_NETTXF_more_data;
+
+               if (!drop_err)
+                       txp++;
+
+       } while (more_data);
 
        if (drop_err) {
                netbk_tx_err(vif, first, cons + slots);
@@ -1408,7 +1420,7 @@ 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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