drop_monitor: Add support for summary alert mode for hardware drops

In summary alert mode a notification is sent with a list of recent drop
reasons and a count of how many packets were dropped due to this reason.

To avoid expensive operations in the context in which packets are
dropped, each CPU holds an array whose number of entries is the maximum
number of drop reasons that can be encoded in the netlink notification.
Each entry stores the drop reason and a count. When a packet is dropped
the array is traversed and a new entry is created or the count of an
existing entry is incremented.

Later, in process context, the array is replaced with a newly allocated
copy and the old array is encoded in a netlink notification. To avoid
breaking user space, the notification includes the ancillary header,
which is 'struct net_dm_alert_msg' with number of entries set to '0'.

Signed-off-by: Ido Schimmel <[email protected]>
Acked-by: Jiri Pirko <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: idosch

include/uapi/linux/net_dropmon.h

@@ -87,6 +87,9 @@ enum net_dm_attr {
 	NET_DM_ATTR_ORIGIN,			/* u16 */
 	NET_DM_ATTR_HW_TRAP_GROUP_NAME,		/* string */
 	NET_DM_ATTR_HW_TRAP_NAME,		/* string */
+	NET_DM_ATTR_HW_ENTRIES,			/* nested */
+	NET_DM_ATTR_HW_ENTRY,			/* nested */
+	NET_DM_ATTR_HW_TRAP_COUNT,		/* u32 */
 
 	__NET_DM_ATTR_MAX,
 	NET_DM_ATTR_MAX = __NET_DM_ATTR_MAX - 1

net/core/drop_monitor.c

@@ -58,9 +58,26 @@ struct net_dm_stats {
 	struct u64_stats_sync syncp;
 };
 
+#define NET_DM_MAX_HW_TRAP_NAME_LEN 40
+
+struct net_dm_hw_entry {
+	char trap_name[NET_DM_MAX_HW_TRAP_NAME_LEN];
+	u32 count;
+};
+
+struct net_dm_hw_entries {
+	u32 num_entries;
+	struct net_dm_hw_entry entries[0];
+};
+
 struct per_cpu_dm_data {
-	spinlock_t		lock;	/* Protects 'skb' and 'send_timer' */
-	struct sk_buff		*skb;
+	spinlock_t		lock;	/* Protects 'skb', 'hw_entries' and
+					 * 'send_timer'
+					 */
+	union {
+		struct sk_buff			*skb;
+		struct net_dm_hw_entries	*hw_entries;
+	};
 	struct sk_buff_head	drop_queue;
 	struct work_struct	dm_alert_work;
 	struct timer_list	send_timer;
@@ -275,16 +292,189 @@ static void trace_napi_poll_hit(void *ignore, struct napi_struct *napi,
 	rcu_read_unlock();
 }
 
+static struct net_dm_hw_entries *
+net_dm_hw_reset_per_cpu_data(struct per_cpu_dm_data *hw_data)
+{
+	struct net_dm_hw_entries *hw_entries;
+	unsigned long flags;
+
+	hw_entries = kzalloc(struct_size(hw_entries, entries, dm_hit_limit),
+			     GFP_KERNEL);
+	if (!hw_entries) {
+		/* If the memory allocation failed, we try to perform another
+		 * allocation in 1/10 second. Otherwise, the probe function
+		 * will constantly bail out.
+		 */
+		mod_timer(&hw_data->send_timer, jiffies + HZ / 10);
+	}
+
+	spin_lock_irqsave(&hw_data->lock, flags);
+	swap(hw_data->hw_entries, hw_entries);
+	spin_unlock_irqrestore(&hw_data->lock, flags);
+
+	return hw_entries;
+}
+
+static int net_dm_hw_entry_put(struct sk_buff *msg,
+			       const struct net_dm_hw_entry *hw_entry)
+{
+	struct nlattr *attr;
+
+	attr = nla_nest_start(msg, NET_DM_ATTR_HW_ENTRY);
+	if (!attr)
+		return -EMSGSIZE;
+
+	if (nla_put_string(msg, NET_DM_ATTR_HW_TRAP_NAME, hw_entry->trap_name))
+		goto nla_put_failure;
+
+	if (nla_put_u32(msg, NET_DM_ATTR_HW_TRAP_COUNT, hw_entry->count))
+		goto nla_put_failure;
+
+	nla_nest_end(msg, attr);
+
+	return 0;
+
+nla_put_failure:
+	nla_nest_cancel(msg, attr);
+	return -EMSGSIZE;
+}
+
+static int net_dm_hw_entries_put(struct sk_buff *msg,
+				 const struct net_dm_hw_entries *hw_entries)
+{
+	struct nlattr *attr;
+	int i;
+
+	attr = nla_nest_start(msg, NET_DM_ATTR_HW_ENTRIES);
+	if (!attr)
+		return -EMSGSIZE;
+
+	for (i = 0; i < hw_entries->num_entries; i++) {
+		int rc;
+
+		rc = net_dm_hw_entry_put(msg, &hw_entries->entries[i]);
+		if (rc)
+			goto nla_put_failure;
+	}
+
+	nla_nest_end(msg, attr);
+
+	return 0;
+
+nla_put_failure:
+	nla_nest_cancel(msg, attr);
+	return -EMSGSIZE;
+}
+
+static int
+net_dm_hw_summary_report_fill(struct sk_buff *msg,
+			      const struct net_dm_hw_entries *hw_entries)
+{
+	struct net_dm_alert_msg anc_hdr = { 0 };
+	void *hdr;
+	int rc;
+
+	hdr = genlmsg_put(msg, 0, 0, &net_drop_monitor_family, 0,
+			  NET_DM_CMD_ALERT);
+	if (!hdr)
+		return -EMSGSIZE;
+
+	/* We need to put the ancillary header in order not to break user
+	 * space.
+	 */
+	if (nla_put(msg, NLA_UNSPEC, sizeof(anc_hdr), &anc_hdr))
+		goto nla_put_failure;
+
+	rc = net_dm_hw_entries_put(msg, hw_entries);
+	if (rc)
+		goto nla_put_failure;
+
+	genlmsg_end(msg, hdr);
+
+	return 0;
+
+nla_put_failure:
+	genlmsg_cancel(msg, hdr);
+	return -EMSGSIZE;
+}
+
+static void net_dm_hw_summary_work(struct work_struct *work)
+{
+	struct net_dm_hw_entries *hw_entries;
+	struct per_cpu_dm_data *hw_data;
+	struct sk_buff *msg;
+	int rc;
+
+	hw_data = container_of(work, struct per_cpu_dm_data, dm_alert_work);
+
+	hw_entries = net_dm_hw_reset_per_cpu_data(hw_data);
+	if (!hw_entries)
+		return;
+
+	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
+	if (!msg)
+		goto out;
+
+	rc = net_dm_hw_summary_report_fill(msg, hw_entries);
+	if (rc) {
+		nlmsg_free(msg);
+		goto out;
+	}
+
+	genlmsg_multicast(&net_drop_monitor_family, msg, 0, 0, GFP_KERNEL);
+
+out:
+	kfree(hw_entries);
+}
+
 static void
 net_dm_hw_summary_probe(struct sk_buff *skb,
 			const struct net_dm_hw_metadata *hw_metadata)
 {
+	struct net_dm_hw_entries *hw_entries;
+	struct net_dm_hw_entry *hw_entry;
+	struct per_cpu_dm_data *hw_data;
+	unsigned long flags;
+	int i;
+
+	hw_data = this_cpu_ptr(&dm_hw_cpu_data);
+	spin_lock_irqsave(&hw_data->lock, flags);
+	hw_entries = hw_data->hw_entries;
+
+	if (!hw_entries)
+		goto out;
+
+	for (i = 0; i < hw_entries->num_entries; i++) {
+		hw_entry = &hw_entries->entries[i];
+		if (!strncmp(hw_entry->trap_name, hw_metadata->trap_name,
+			     NET_DM_MAX_HW_TRAP_NAME_LEN - 1)) {
+			hw_entry->count++;
+			goto out;
+		}
+	}
+	if (WARN_ON_ONCE(hw_entries->num_entries == dm_hit_limit))
+		goto out;
+
+	hw_entry = &hw_entries->entries[hw_entries->num_entries];
+	strlcpy(hw_entry->trap_name, hw_metadata->trap_name,
+		NET_DM_MAX_HW_TRAP_NAME_LEN - 1);
+	hw_entry->count = 1;
+	hw_entries->num_entries++;
+
+	if (!timer_pending(&hw_data->send_timer)) {
+		hw_data->send_timer.expires = jiffies + dm_delay * HZ;
+		add_timer(&hw_data->send_timer);
+	}
+
+out:
+	spin_unlock_irqrestore(&hw_data->lock, flags);
 }
 
 static const struct net_dm_alert_ops net_dm_alert_summary_ops = {
 	.kfree_skb_probe	= trace_kfree_skb_hit,
 	.napi_poll_probe	= trace_napi_poll_hit,
 	.work_item_func		= send_dm_alert,
+	.hw_work_item_func	= net_dm_hw_summary_work,
 	.hw_probe		= net_dm_hw_summary_probe,
 };
 
@@ -1309,6 +1499,7 @@ static void net_dm_hw_cpu_data_fini(int cpu)
 	struct per_cpu_dm_data *hw_data;
 
 	hw_data = &per_cpu(dm_hw_cpu_data, cpu);
+	kfree(hw_data->hw_entries);
 	__net_dm_cpu_data_fini(hw_data);
 }