drop_monitor: Make drop queue length configurable

In packet alert mode, each CPU holds a list of dropped skbs that need to
be processed in process context and sent to user space. To avoid
exhausting the system's memory the maximum length of this queue is
currently set to 1000.

Allow users to tune the length of this queue according to their needs.
The configured length is reported to user space when drop monitor
configuration is queried.
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/net_dropmon.h

@@ -79,6 +79,7 @@ enum net_dm_attr {
 	NET_DM_ATTR_PAD,
 	NET_DM_ATTR_TRUNC_LEN,			/* u32 */
 	NET_DM_ATTR_ORIG_LEN,			/* u32 */
+	NET_DM_ATTR_QUEUE_LEN,			/* u32 */
 
 	__NET_DM_ATTR_MAX,
 	NET_DM_ATTR_MAX = __NET_DM_ATTR_MAX - 1

net/core/drop_monitor.c

@@ -78,6 +78,7 @@ static LIST_HEAD(hw_stats_list);
 
 static enum net_dm_alert_mode net_dm_alert_mode = NET_DM_ALERT_MODE_SUMMARY;
 static u32 net_dm_trunc_len;
+static u32 net_dm_queue_len = 1000;
 
 struct net_dm_alert_ops {
 	void (*kfree_skb_probe)(void *ignore, struct sk_buff *skb,
@@ -93,8 +94,6 @@ struct net_dm_skb_cb {
 
 #define NET_DM_SKB_CB(__skb) ((struct net_dm_skb_cb *)&((__skb)->cb[0]))
 
-#define NET_DM_QUEUE_LEN 1000
-
 static struct sk_buff *reset_per_cpu_data(struct per_cpu_dm_data *data)
 {
 	size_t al;
@@ -289,7 +288,7 @@ static void net_dm_packet_trace_kfree_skb_hit(void *ignore,
 	data = this_cpu_ptr(&dm_cpu_data);
 
 	spin_lock_irqsave(&data->drop_queue.lock, flags);
-	if (skb_queue_len(&data->drop_queue) < NET_DM_QUEUE_LEN)
+	if (skb_queue_len(&data->drop_queue) < net_dm_queue_len)
 		__skb_queue_tail(&data->drop_queue, nskb);
 	else
 		goto unlock_free;
@@ -643,6 +642,14 @@ static void net_dm_trunc_len_set(struct genl_info *info)
 	net_dm_trunc_len = nla_get_u32(info->attrs[NET_DM_ATTR_TRUNC_LEN]);
 }
 
+static void net_dm_queue_len_set(struct genl_info *info)
+{
+	if (!info->attrs[NET_DM_ATTR_QUEUE_LEN])
+		return;
+
+	net_dm_queue_len = nla_get_u32(info->attrs[NET_DM_ATTR_QUEUE_LEN]);
+}
+
 static int net_dm_cmd_config(struct sk_buff *skb,
 			struct genl_info *info)
 {
@@ -660,6 +667,8 @@ static int net_dm_cmd_config(struct sk_buff *skb,
 
 	net_dm_trunc_len_set(info);
 
+	net_dm_queue_len_set(info);
+
 	return 0;
 }
 
@@ -691,6 +700,9 @@ static int net_dm_config_fill(struct sk_buff *msg, struct genl_info *info)
 	if (nla_put_u32(msg, NET_DM_ATTR_TRUNC_LEN, net_dm_trunc_len))
 		goto nla_put_failure;
 
+	if (nla_put_u32(msg, NET_DM_ATTR_QUEUE_LEN, net_dm_queue_len))
+		goto nla_put_failure;
+
 	genlmsg_end(msg, hdr);
 
 	return 0;
@@ -763,6 +775,7 @@ static const struct nla_policy net_dm_nl_policy[NET_DM_ATTR_MAX + 1] = {
 	[NET_DM_ATTR_UNSPEC] = { .strict_start_type = NET_DM_ATTR_UNSPEC + 1 },
 	[NET_DM_ATTR_ALERT_MODE] = { .type = NLA_U8 },
 	[NET_DM_ATTR_TRUNC_LEN] = { .type = NLA_U32 },
+	[NET_DM_ATTR_QUEUE_LEN] = { .type = NLA_U32 },
 };
 
 static const struct genl_ops dropmon_ops[] = {