[RFC PATCH net-next 10/12] drop_monitor: Add packet alert mode

[Ido Schimmel <idosch@idosch.org>]

From: Ido Schimmel <idosch@mellanox.com>

So far drop monitor supported only one alert mode in which a summary of
locations in which packets were recently dropped was sent to user space.

This alert mode is sufficient in order to understand that packets were
dropped, but lacks information to perform a more detailed analysis.

Add a new alert mode in which the dropped packet itself is passed to
user space along with metadata: The drop location (as program counter
and resolved symbol), ingress / egress netdevice and arrival / departure
timestamp. More metadata can be added in the future.

To avoid performing expensive operations in the context in which
kfree_skb() is invoked (can be hard IRQ), the dropped skb is cloned and
queued on per-CPU skb drop list. Then, in process context the netlink
message is allocated, prepared and finally sent to user space.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
---
 include/uapi/linux/net_dropmon.h |  29 ++++
 net/core/drop_monitor.c          | 287 ++++++++++++++++++++++++++++++-
 2 files changed, 308 insertions(+), 8 deletions(-)

diff --git a/include/uapi/linux/net_dropmon.h b/include/uapi/linux/net_dropmon.h
index 5edbd0a675fd..7708c8a440a1 100644
--- a/include/uapi/linux/net_dropmon.h
+++ b/include/uapi/linux/net_dropmon.h
@@ -53,6 +53,7 @@ enum {
 	NET_DM_CMD_CONFIG,
 	NET_DM_CMD_START,
 	NET_DM_CMD_STOP,
+	NET_DM_CMD_PACKET_ALERT,
 	_NET_DM_CMD_MAX,
 };
 
@@ -62,4 +63,32 @@ enum {
  * Our group identifiers
  */
 #define NET_DM_GRP_ALERT 1
+
+enum net_dm_attr {
+	NET_DM_ATTR_UNSPEC,
+
+	NET_DM_ATTR_ALERT_MODE,			/* u8 */
+	NET_DM_ATTR_PC,				/* u64 */
+	NET_DM_ATTR_SYMBOL,			/* string */
+	NET_DM_ATTR_NETDEV_IFINDEX,		/* u32 */
+	NET_DM_ATTR_NETDEV_NAME,		/* string */
+	NET_DM_ATTR_TIMESTAMP,			/* struct timespec */
+	NET_DM_ATTR_PAYLOAD,			/* binary */
+	NET_DM_ATTR_PAD,
+
+	__NET_DM_ATTR_MAX,
+	NET_DM_ATTR_MAX = __NET_DM_ATTR_MAX - 1
+};
+
+/**
+ * enum net_dm_alert_mode - Alert mode.
+ * @NET_DM_ALERT_MODE_SUMMARY: A summary of recent drops is sent to user space.
+ * @NET_DM_ALERT_MODE_PACKET: Each dropped packet is sent to user space along
+ *                            with metadata.
+ */
+enum net_dm_alert_mode {
+	NET_DM_ALERT_MODE_SUMMARY,
+	NET_DM_ALERT_MODE_PACKET,
+};
+
 #endif
diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index f441fb653567..512935fc235b 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -54,6 +54,7 @@ static DEFINE_MUTEX(net_dm_mutex);
 struct per_cpu_dm_data {
 	spinlock_t		lock;	/* Protects 'skb' and 'send_timer' */
 	struct sk_buff		*skb;
+	struct sk_buff_head	drop_queue;
 	struct work_struct	dm_alert_work;
 	struct timer_list	send_timer;
 };
@@ -75,6 +76,22 @@ static int dm_delay = 1;
 static unsigned long dm_hw_check_delta = 2*HZ;
 static LIST_HEAD(hw_stats_list);
 
+static enum net_dm_alert_mode net_dm_alert_mode = NET_DM_ALERT_MODE_SUMMARY;
+
+struct net_dm_skb_cb {
+	void *pc;
+};
+
+#define NET_DM_SKB_CB(__skb) ((struct net_dm_skb_cb *)&((__skb)->cb[0]))
+
+struct net_dm_alert_ops {
+	void (*kfree_skb_probe)(void *ignore, struct sk_buff *skb,
+				void *location);
+	void (*napi_poll_probe)(void *ignore, struct napi_struct *napi,
+				int work, int budget);
+	void (*work_item_func)(struct work_struct *work);
+};
+
 static int net_dm_nl_pre_doit(const struct genl_ops *ops,
 			      struct sk_buff *skb, struct genl_info *info)
 {
@@ -255,10 +272,194 @@ static void trace_napi_poll_hit(void *ignore, struct napi_struct *napi,
 	rcu_read_unlock();
 }
 
+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,
+};
+
+static void net_dm_packet_trace_kfree_skb_hit(void *ignore,
+					      struct sk_buff *skb,
+					      void *location)
+{
+	struct per_cpu_dm_data *data;
+	struct sk_buff *nskb;
+	unsigned long flags;
+
+	nskb = skb_clone(skb, GFP_ATOMIC);
+	if (!nskb)
+		return;
+
+	NET_DM_SKB_CB(nskb)->pc = location;
+	if (nskb->dev)
+		dev_hold(nskb->dev);
+
+	data = this_cpu_ptr(&dm_cpu_data);
+	spin_lock_irqsave(&data->drop_queue.lock, flags);
+
+	__skb_queue_tail(&data->drop_queue, nskb);
+
+	if (!timer_pending(&data->send_timer)) {
+		data->send_timer.expires = jiffies + dm_delay * HZ;
+		add_timer(&data->send_timer);
+	}
+
+	spin_unlock_irqrestore(&data->drop_queue.lock, flags);
+}
+
+static void net_dm_packet_trace_napi_poll_hit(void *ignore,
+					      struct napi_struct *napi,
+					      int work, int budget)
+{
+}
+
+#define NET_DM_MAX_SYMBOL_LEN 40
+
+static size_t net_dm_packet_report_size(size_t payload_len)
+{
+	size_t size;
+
+	size = nlmsg_msg_size(GENL_HDRLEN + net_drop_monitor_family.hdrsize);
+
+	return NLMSG_ALIGN(size) +
+	       /* NET_DM_ATTR_PC */
+	       nla_total_size(sizeof(u64)) +
+	       /* NET_DM_ATTR_SYMBOL */
+	       nla_total_size(NET_DM_MAX_SYMBOL_LEN + 1) +
+	       /* NET_DM_ATTR_NETDEV_IFINDEX */
+	       nla_total_size(sizeof(u32)) +
+	       /* NET_DM_ATTR_NETDEV_NAME */
+	       nla_total_size(IFNAMSIZ + 1) +
+	       /* NET_DM_ATTR_TIMESTAMP */
+	       nla_total_size(sizeof(struct timespec)) +
+	       /* NET_DM_ATTR_PAYLOAD */
+	       nla_total_size(payload_len);
+}
+
+static int net_dm_packet_report_fill(struct sk_buff *msg, struct sk_buff *skb,
+				     size_t payload_len)
+{
+	u64 pc = (u64)(uintptr_t) NET_DM_SKB_CB(skb)->pc;
+	char buf[NET_DM_MAX_SYMBOL_LEN];
+	struct nlattr *attr;
+	struct timespec ts;
+	void *hdr;
+
+	hdr = genlmsg_put(msg, 0, 0, &net_drop_monitor_family, 0,
+			  NET_DM_CMD_PACKET_ALERT);
+	if (!hdr)
+		return -EMSGSIZE;
+
+	if (nla_put_u64_64bit(msg, NET_DM_ATTR_PC, pc, NET_DM_ATTR_PAD))
+		goto nla_put_failure;
+
+	snprintf(buf, sizeof(buf), "%pS", NET_DM_SKB_CB(skb)->pc);
+	if (nla_put_string(msg, NET_DM_ATTR_SYMBOL, buf))
+		goto nla_put_failure;
+
+	if (skb->dev &&
+	    nla_put_u32(msg, NET_DM_ATTR_NETDEV_IFINDEX, skb->dev->ifindex))
+		goto nla_put_failure;
+
+	if (skb->dev &&
+	    nla_put_string(msg, NET_DM_ATTR_NETDEV_NAME, skb->dev->name))
+		goto nla_put_failure;
+
+	if (ktime_to_timespec_cond(skb->tstamp, &ts) &&
+	    nla_put(msg, NET_DM_ATTR_TIMESTAMP, sizeof(ts), &ts))
+		goto nla_put_failure;
+
+	if (!payload_len)
+		goto out;
+
+	attr = skb_put(msg, nla_total_size(payload_len));
+	attr->nla_type = NET_DM_ATTR_PAYLOAD;
+	attr->nla_len = nla_attr_size(payload_len);
+	if (skb_copy_bits(skb, 0, nla_data(attr), payload_len))
+		goto nla_put_failure;
+
+out:
+	genlmsg_end(msg, hdr);
+
+	return 0;
+
+nla_put_failure:
+	genlmsg_cancel(msg, hdr);
+	return -EMSGSIZE;
+}
+
+#define NET_DM_MAX_PACKET_SIZE (0xffff - NLA_HDRLEN - NLA_ALIGNTO)
+
+static void net_dm_packet_report(struct sk_buff *skb)
+{
+	struct sk_buff *msg;
+	size_t payload_len;
+	int rc;
+
+	/* Make sure we start copying the packet from the MAC header */
+	if (skb->data > skb_mac_header(skb))
+		skb_push(skb, skb->data - skb_mac_header(skb));
+	else
+		skb_pull(skb, skb_mac_header(skb) - skb->data);
+
+	/* Ensure packet fits inside a single netlink attribute */
+	payload_len = min_t(size_t, skb->len, NET_DM_MAX_PACKET_SIZE);
+
+	msg = nlmsg_new(net_dm_packet_report_size(payload_len), GFP_KERNEL);
+	if (!msg)
+		goto out;
+
+	rc = net_dm_packet_report_fill(msg, skb, payload_len);
+	if (rc) {
+		nlmsg_free(msg);
+		goto out;
+	}
+
+	genlmsg_multicast(&net_drop_monitor_family, msg, 0, 0, GFP_KERNEL);
+
+out:
+	if (skb->dev)
+		dev_put(skb->dev);
+	consume_skb(skb);
+}
+
+static void net_dm_packet_work(struct work_struct *work)
+{
+	struct per_cpu_dm_data *data;
+	struct sk_buff_head list;
+	struct sk_buff *skb;
+	unsigned long flags;
+
+	data = container_of(work, struct per_cpu_dm_data, dm_alert_work);
+
+	__skb_queue_head_init(&list);
+
+	spin_lock_irqsave(&data->drop_queue.lock, flags);
+	skb_queue_splice_tail_init(&data->drop_queue, &list);
+	spin_unlock_irqrestore(&data->drop_queue.lock, flags);
+
+	while ((skb = __skb_dequeue(&list)))
+		net_dm_packet_report(skb);
+}
+
+static const struct net_dm_alert_ops net_dm_alert_packet_ops = {
+	.kfree_skb_probe	= net_dm_packet_trace_kfree_skb_hit,
+	.napi_poll_probe	= net_dm_packet_trace_napi_poll_hit,
+	.work_item_func		= net_dm_packet_work,
+};
+
+static const struct net_dm_alert_ops *net_dm_alert_ops_arr[] = {
+	[NET_DM_ALERT_MODE_SUMMARY]	= &net_dm_alert_summary_ops,
+	[NET_DM_ALERT_MODE_PACKET]	= &net_dm_alert_packet_ops,
+};
+
 static int net_dm_trace_on_set(struct netlink_ext_ack *extack)
 {
+	const struct net_dm_alert_ops *ops;
 	int cpu, rc;
 
+	ops = net_dm_alert_ops_arr[net_dm_alert_mode];
+
 	if (!try_module_get(THIS_MODULE)) {
 		NL_SET_ERR_MSG_MOD(extack, "Failed to take reference on module");
 		return -ENODEV;
@@ -267,17 +468,17 @@ static int net_dm_trace_on_set(struct netlink_ext_ack *extack)
 	for_each_possible_cpu(cpu) {
 		struct per_cpu_dm_data *data = &per_cpu(dm_cpu_data, cpu);
 
-		INIT_WORK(&data->dm_alert_work, send_dm_alert);
+		INIT_WORK(&data->dm_alert_work, ops->work_item_func);
 		timer_setup(&data->send_timer, sched_send_work, 0);
 	}
 
-	rc = register_trace_kfree_skb(trace_kfree_skb_hit, NULL);
+	rc = register_trace_kfree_skb(ops->kfree_skb_probe, NULL);
 	if (rc) {
 		NL_SET_ERR_MSG_MOD(extack, "Failed to connect probe to kfree_skb() tracepoint");
 		goto err_module_put;
 	}
 
-	rc = register_trace_napi_poll(trace_napi_poll_hit, NULL);
+	rc = register_trace_napi_poll(ops->napi_poll_probe, NULL);
 	if (rc) {
 		NL_SET_ERR_MSG_MOD(extack, "Failed to connect probe to napi_poll() tracepoint");
 		goto err_unregister_trace;
@@ -286,7 +487,7 @@ static int net_dm_trace_on_set(struct netlink_ext_ack *extack)
 	return 0;
 
 err_unregister_trace:
-	unregister_trace_kfree_skb(trace_kfree_skb_hit, NULL);
+	unregister_trace_kfree_skb(ops->kfree_skb_probe, NULL);
 err_module_put:
 	module_put(THIS_MODULE);
 	return rc;
@@ -295,10 +496,13 @@ static int net_dm_trace_on_set(struct netlink_ext_ack *extack)
 static void net_dm_trace_off_set(void)
 {
 	struct dm_hw_stat_delta *new_stat, *temp;
+	const struct net_dm_alert_ops *ops;
 	int cpu;
 
-	unregister_trace_napi_poll(trace_napi_poll_hit, NULL);
-	unregister_trace_kfree_skb(trace_kfree_skb_hit, NULL);
+	ops = net_dm_alert_ops_arr[net_dm_alert_mode];
+
+	unregister_trace_napi_poll(ops->napi_poll_probe, NULL);
+	unregister_trace_kfree_skb(ops->kfree_skb_probe, NULL);
 
 	tracepoint_synchronize_unregister();
 
@@ -307,9 +511,18 @@ static void net_dm_trace_off_set(void)
 	 */
 	for_each_possible_cpu(cpu) {
 		struct per_cpu_dm_data *data = &per_cpu(dm_cpu_data, cpu);
+		struct sk_buff *skb;
 
 		del_timer_sync(&data->send_timer);
 		cancel_work_sync(&data->dm_alert_work);
+		/* If we deactivated a pending timer, some packets are still
+		 * queued and we need to free them.
+		 */
+		while ((skb = __skb_dequeue(&data->drop_queue))) {
+			if (skb->dev)
+				dev_put(skb->dev);
+			consume_skb(skb);
+		}
 	}
 
 	list_for_each_entry_safe(new_stat, temp, &hw_stats_list, list) {
@@ -351,12 +564,61 @@ static int set_all_monitor_traces(int state, struct netlink_ext_ack *extack)
 	return rc;
 }
 
+static int net_dm_alert_mode_get_from_info(struct genl_info *info,
+					   enum net_dm_alert_mode *p_alert_mode)
+{
+	u8 val;
+
+	val = nla_get_u8(info->attrs[NET_DM_ATTR_ALERT_MODE]);
+
+	switch (val) {
+	case NET_DM_ALERT_MODE_SUMMARY: /* fall-through */
+	case NET_DM_ALERT_MODE_PACKET:
+		*p_alert_mode = val;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int net_dm_alert_mode_set(struct genl_info *info)
+{
+	struct netlink_ext_ack *extack = info->extack;
+	enum net_dm_alert_mode alert_mode;
+	int rc;
+
+	if (!info->attrs[NET_DM_ATTR_ALERT_MODE])
+		return 0;
+
+	rc = net_dm_alert_mode_get_from_info(info, &alert_mode);
+	if (rc) {
+		NL_SET_ERR_MSG_MOD(extack, "Invalid alert mode");
+		return -EINVAL;
+	}
+
+	net_dm_alert_mode = alert_mode;
+
+	return 0;
+}
+
 static int net_dm_cmd_config(struct sk_buff *skb,
 			struct genl_info *info)
 {
-	NL_SET_ERR_MSG_MOD(info->extack, "Command not supported");
+	struct netlink_ext_ack *extack = info->extack;
+	int rc;
 
-	return -EOPNOTSUPP;
+	if (trace_state == TRACE_ON) {
+		NL_SET_ERR_MSG_MOD(extack, "Cannot configure drop monitor while tracing is on");
+		return -EOPNOTSUPP;
+	}
+
+	rc = net_dm_alert_mode_set(info);
+	if (rc)
+		return rc;
+
+	return 0;
 }
 
 static int net_dm_cmd_trace(struct sk_buff *skb,
@@ -411,6 +673,11 @@ static int dropmon_net_event(struct notifier_block *ev_block,
 	return NOTIFY_DONE;
 }
 
+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 },
+};
+
 static const struct genl_ops dropmon_ops[] = {
 	{
 		.cmd = NET_DM_CMD_CONFIG,
@@ -434,6 +701,8 @@ static struct genl_family net_drop_monitor_family __ro_after_init = {
 	.hdrsize        = 0,
 	.name           = "NET_DM",
 	.version        = 2,
+	.maxattr	= NET_DM_ATTR_MAX,
+	.policy		= net_dm_nl_policy,
 	.pre_doit	= net_dm_nl_pre_doit,
 	.post_doit	= net_dm_nl_post_doit,
 	.module		= THIS_MODULE,
@@ -479,6 +748,7 @@ static int __init init_net_drop_monitor(void)
 		INIT_WORK(&data->dm_alert_work, send_dm_alert);
 		timer_setup(&data->send_timer, sched_send_work, 0);
 		spin_lock_init(&data->lock);
+		skb_queue_head_init(&data->drop_queue);
 		reset_per_cpu_data(data);
 	}
 
@@ -509,6 +779,7 @@ static void exit_net_drop_monitor(void)
 		 * to this struct and can free the skb inside it
 		 */
 		kfree_skb(data->skb);
+		WARN_ON(!skb_queue_empty(&data->drop_queue));
 	}
 
 	BUG_ON(genl_unregister_family(&net_drop_monitor_family));
-- 
2.21.0