Merge branch 'netconsole-allow-userdata-buffer-to-grow-dynamically'

Gustavo Luiz Duarte says:

====================
netconsole: Allow userdata buffer to grow dynamically

The current netconsole implementation allocates a static buffer for
extradata (userdata + sysdata) with a fixed size of
MAX_EXTRADATA_ENTRY_LEN * MAX_EXTRADATA_ITEMS bytes for every target,
regardless of whether userspace actually uses this feature. This forces
us to keep MAX_EXTRADATA_ITEMS small (16), which is restrictive for
users who need to attach more metadata to their log messages.

This patch series enables dynamic allocation of the userdata buffer,
allowing it to grow on-demand based on actual usage. The series:

1. Refactors send_fragmented_body() to simplify handling of separated
   userdata and sysdata (patch 1/4)
2. Splits userdata and sysdata into separate buffers (patch 2/4)
3. Implements dynamic allocation for the userdata buffer (patch 3/4)
4. Increases MAX_USERDATA_ITEMS from 16 to 256 now that we can do so
   without memory waste (patch 4/4)

Benefits:
- No memory waste when userdata is not used
- Targets that use userdata only consume what they need
- Users can attach significantly more metadata without impacting systems
  that don't use this feature
====================

Link: https://patch.msgid.link/20251119-netconsole_dynamic_extradata-v3-0-497ac3191707@meta.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 195 insertions, 193 deletions

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index bb6e03a92956..9cb4dfc242f5 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -50,7 +50,7 @@ MODULE_LICENSE("GPL");
 /* The number 3 comes from userdata entry format characters (' ', '=', '\n') */
 #define MAX_EXTRADATA_NAME_LEN		(MAX_EXTRADATA_ENTRY_LEN - \
 					MAX_EXTRADATA_VALUE_LEN - 3)
-#define MAX_EXTRADATA_ITEMS		16
+#define MAX_USERDATA_ITEMS		256
 #define MAX_PRINT_CHUNK			1000
 
 static char config[MAX_PARAM_LENGTH];
@@ -115,6 +115,8 @@ enum sysdata_feature {
 	SYSDATA_RELEASE = BIT(2),
 	/* Include a per-target message ID as part of sysdata */
 	SYSDATA_MSGID = BIT(3),
+	/* Sentinel: highest bit position */
+	MAX_SYSDATA_ITEMS = 4,
 };
 
 /**
@@ -122,8 +124,9 @@ enum sysdata_feature {
  * @list:	Links this target into the target_list.
  * @group:	Links us into the configfs subsystem hierarchy.
  * @userdata_group:	Links to the userdata configfs hierarchy
- * @extradata_complete:	Cached, formatted string of append
- * @userdata_length:	String length of usedata in extradata_complete.
+ * @userdata:		Cached, formatted string of append
+ * @userdata_length:	String length of userdata.
+ * @sysdata:		Cached, formatted string of append
  * @sysdata_fields:	Sysdata features enabled.
  * @msgcounter:	Message sent counter.
  * @stats:	Packet send stats for the target. Used for debugging.
@@ -152,8 +155,10 @@ struct netconsole_target {
 #ifdef	CONFIG_NETCONSOLE_DYNAMIC
 	struct config_group	group;
 	struct config_group	userdata_group;
-	char extradata_complete[MAX_EXTRADATA_ENTRY_LEN * MAX_EXTRADATA_ITEMS];
+	char			*userdata;
 	size_t			userdata_length;
+	char			sysdata[MAX_EXTRADATA_ENTRY_LEN * MAX_SYSDATA_ITEMS];
+
 	/* bit-wise with sysdata_feature bits */
 	u32			sysdata_fields;
 	/* protected by target_list_lock */
@@ -802,28 +807,14 @@ out_unlock:
 	return ret;
 }
 
-/* Count number of entries we have in extradata.
- * This is important because the extradata_complete only supports
- * MAX_EXTRADATA_ITEMS entries. Before enabling any new {user,sys}data
- * feature, number of entries needs to checked for available space.
+/* Count number of entries we have in userdata.
+ * This is important because userdata only supports MAX_USERDATA_ITEMS
+ * entries. Before enabling any new userdata feature, number of entries needs
+ * to checked for available space.
  */
-static size_t count_extradata_entries(struct netconsole_target *nt)
+static size_t count_userdata_entries(struct netconsole_target *nt)
 {
-	size_t entries;
-
-	/* Userdata entries */
-	entries = list_count_nodes(&nt->userdata_group.cg_children);
-	/* Plus sysdata entries */
-	if (nt->sysdata_fields & SYSDATA_CPU_NR)
-		entries += 1;
-	if (nt->sysdata_fields & SYSDATA_TASKNAME)
-		entries += 1;
-	if (nt->sysdata_fields & SYSDATA_RELEASE)
-		entries += 1;
-	if (nt->sysdata_fields & SYSDATA_MSGID)
-		entries += 1;
-
-	return entries;
+	return list_count_nodes(&nt->userdata_group.cg_children);
 }
 
 static ssize_t remote_mac_store(struct config_item *item, const char *buf,
@@ -884,45 +875,77 @@ static ssize_t userdatum_value_show(struct config_item *item, char *buf)
 	return sysfs_emit(buf, "%s\n", &(to_userdatum(item)->value[0]));
 }
 
-static void update_userdata(struct netconsole_target *nt)
+/* Navigate configfs and calculate the lentgh of the formatted string
+ * representing userdata.
+ * Must be called holding netconsole_subsys.su_mutex
+ */
+static int calc_userdata_len(struct netconsole_target *nt)
 {
+	struct userdatum *udm_item;
+	struct config_item *item;
 	struct list_head *entry;
-	int child_count = 0;
-	unsigned long flags;
+	int len = 0;
 
-	spin_lock_irqsave(&target_list_lock, flags);
+	list_for_each(entry, &nt->userdata_group.cg_children) {
+		item = container_of(entry, struct config_item, ci_entry);
+		udm_item = to_userdatum(item);
+		/* Skip userdata with no value set */
+		if (udm_item->value[0]) {
+			len += snprintf(NULL, 0, " %s=%s\n", item->ci_name,
+					udm_item->value);
+		}
+	}
+	return len;
+}
 
-	/* Clear the current string in case the last userdatum was deleted */
-	nt->userdata_length = 0;
-	nt->extradata_complete[0] = 0;
+static int update_userdata(struct netconsole_target *nt)
+{
+	struct userdatum *udm_item;
+	struct config_item *item;
+	struct list_head *entry;
+	char *old_buf = NULL;
+	char *new_buf = NULL;
+	unsigned long flags;
+	int offset = 0;
+	int len;
 
-	list_for_each(entry, &nt->userdata_group.cg_children) {
-		struct userdatum *udm_item;
-		struct config_item *item;
+	/* Calculate required buffer size */
+	len = calc_userdata_len(nt);
 
-		if (child_count >= MAX_EXTRADATA_ITEMS) {
-			spin_unlock_irqrestore(&target_list_lock, flags);
-			WARN_ON_ONCE(1);
-			return;
-		}
-		child_count++;
+	if (WARN_ON_ONCE(len > MAX_EXTRADATA_ENTRY_LEN * MAX_USERDATA_ITEMS))
+		return -ENOSPC;
+
+	/* Allocate new buffer */
+	if (len) {
+		new_buf = kmalloc(len + 1, GFP_KERNEL);
+		if (!new_buf)
+			return -ENOMEM;
+	}
 
+	/* Write userdata to new buffer */
+	list_for_each(entry, &nt->userdata_group.cg_children) {
 		item = container_of(entry, struct config_item, ci_entry);
 		udm_item = to_userdatum(item);
-
 		/* Skip userdata with no value set */
-		if (strnlen(udm_item->value, MAX_EXTRADATA_VALUE_LEN) == 0)
-			continue;
-
-		/* This doesn't overflow extradata_complete since it will write
-		 * one entry length (1/MAX_EXTRADATA_ITEMS long), entry count is
-		 * checked to not exceed MAX items with child_count above
-		 */
-		nt->userdata_length += scnprintf(&nt->extradata_complete[nt->userdata_length],
-						 MAX_EXTRADATA_ENTRY_LEN, " %s=%s\n",
-						 item->ci_name, udm_item->value);
+		if (udm_item->value[0]) {
+			offset += scnprintf(&new_buf[offset], len + 1 - offset,
+					    " %s=%s\n", item->ci_name,
+					    udm_item->value);
+		}
 	}
+
+	WARN_ON_ONCE(offset != len);
+
+	/* Switch to new buffer and free old buffer */
+	spin_lock_irqsave(&target_list_lock, flags);
+	old_buf = nt->userdata;
+	nt->userdata = new_buf;
+	nt->userdata_length = offset;
 	spin_unlock_irqrestore(&target_list_lock, flags);
+
+	kfree(old_buf);
+
+	return 0;
 }
 
 static ssize_t userdatum_value_store(struct config_item *item, const char *buf,
@@ -946,7 +969,9 @@ static ssize_t userdatum_value_store(struct config_item *item, const char *buf,
 
 	ud = to_userdata(item->ci_parent);
 	nt = userdata_to_target(ud);
-	update_userdata(nt);
+	ret = update_userdata(nt);
+	if (ret < 0)
+		goto out_unlock;
 	ret = count;
 out_unlock:
 	mutex_unlock(&dynamic_netconsole_mutex);
@@ -962,7 +987,7 @@ static void disable_sysdata_feature(struct netconsole_target *nt,
 				    enum sysdata_feature feature)
 {
 	nt->sysdata_fields &= ~feature;
-	nt->extradata_complete[nt->userdata_length] = 0;
+	nt->sysdata[0] = 0;
 }
 
 static ssize_t sysdata_msgid_enabled_store(struct config_item *item,
@@ -982,12 +1007,6 @@ static ssize_t sysdata_msgid_enabled_store(struct config_item *item,
 	if (msgid_enabled == curr)
 		goto unlock_ok;
 
-	if (msgid_enabled &&
-	    count_extradata_entries(nt) >= MAX_EXTRADATA_ITEMS) {
-		ret = -ENOSPC;
-		goto unlock;
-	}
-
 	if (msgid_enabled)
 		nt->sysdata_fields |= SYSDATA_MSGID;
 	else
@@ -995,7 +1014,6 @@ static ssize_t sysdata_msgid_enabled_store(struct config_item *item,
 
 unlock_ok:
 	ret = strnlen(buf, count);
-unlock:
 	mutex_unlock(&dynamic_netconsole_mutex);
 	mutex_unlock(&netconsole_subsys.su_mutex);
 	return ret;
@@ -1018,12 +1036,6 @@ static ssize_t sysdata_release_enabled_store(struct config_item *item,
 	if (release_enabled == curr)
 		goto unlock_ok;
 
-	if (release_enabled &&
-	    count_extradata_entries(nt) >= MAX_EXTRADATA_ITEMS) {
-		ret = -ENOSPC;
-		goto unlock;
-	}
-
 	if (release_enabled)
 		nt->sysdata_fields |= SYSDATA_RELEASE;
 	else
@@ -1031,7 +1043,6 @@ static ssize_t sysdata_release_enabled_store(struct config_item *item,
 
 unlock_ok:
 	ret = strnlen(buf, count);
-unlock:
 	mutex_unlock(&dynamic_netconsole_mutex);
 	mutex_unlock(&netconsole_subsys.su_mutex);
 	return ret;
@@ -1054,12 +1065,6 @@ static ssize_t sysdata_taskname_enabled_store(struct config_item *item,
 	if (taskname_enabled == curr)
 		goto unlock_ok;
 
-	if (taskname_enabled &&
-	    count_extradata_entries(nt) >= MAX_EXTRADATA_ITEMS) {
-		ret = -ENOSPC;
-		goto unlock;
-	}
-
 	if (taskname_enabled)
 		nt->sysdata_fields |= SYSDATA_TASKNAME;
 	else
@@ -1067,7 +1072,6 @@ static ssize_t sysdata_taskname_enabled_store(struct config_item *item,
 
 unlock_ok:
 	ret = strnlen(buf, count);
-unlock:
 	mutex_unlock(&dynamic_netconsole_mutex);
 	mutex_unlock(&netconsole_subsys.su_mutex);
 	return ret;
@@ -1092,27 +1096,16 @@ static ssize_t sysdata_cpu_nr_enabled_store(struct config_item *item,
 		/* no change requested */
 		goto unlock_ok;
 
-	if (cpu_nr_enabled &&
-	    count_extradata_entries(nt) >= MAX_EXTRADATA_ITEMS) {
-		/* user wants the new feature, but there is no space in the
-		 * buffer.
-		 */
-		ret = -ENOSPC;
-		goto unlock;
-	}
-
 	if (cpu_nr_enabled)
 		nt->sysdata_fields |= SYSDATA_CPU_NR;
 	else
-		/* This is special because extradata_complete might have
-		 * remaining data from previous sysdata, and it needs to be
-		 * cleaned.
+		/* This is special because sysdata might have remaining data
+		 * from previous sysdata, and it needs to be cleaned.
 		 */
 		disable_sysdata_feature(nt, SYSDATA_CPU_NR);
 
 unlock_ok:
 	ret = strnlen(buf, count);
-unlock:
 	mutex_unlock(&dynamic_netconsole_mutex);
 	mutex_unlock(&netconsole_subsys.su_mutex);
 	return ret;
@@ -1156,7 +1149,7 @@ static struct config_item *userdatum_make_item(struct config_group *group,
 
 	ud = to_userdata(&group->cg_item);
 	nt = userdata_to_target(ud);
-	if (count_extradata_entries(nt) >= MAX_EXTRADATA_ITEMS)
+	if (count_userdata_entries(nt) >= MAX_USERDATA_ITEMS)
 		return ERR_PTR(-ENOSPC);
 
 	udm = kzalloc(sizeof(*udm), GFP_KERNEL);
@@ -1234,7 +1227,10 @@ static struct configfs_attribute *netconsole_target_attrs[] = {
 
 static void netconsole_target_release(struct config_item *item)
 {
-	kfree(to_target(item));
+	struct netconsole_target *nt = to_target(item);
+
+	kfree(nt->userdata);
+	kfree(nt);
 }
 
 static struct configfs_item_operations netconsole_target_item_ops = {
@@ -1363,22 +1359,21 @@ static void populate_configfs_item(struct netconsole_target *nt,
 
 static int sysdata_append_cpu_nr(struct netconsole_target *nt, int offset)
 {
-	/* Append cpu=%d at extradata_complete after userdata str */
-	return scnprintf(&nt->extradata_complete[offset],
+	return scnprintf(&nt->sysdata[offset],
 			 MAX_EXTRADATA_ENTRY_LEN, " cpu=%u\n",
 			 raw_smp_processor_id());
 }
 
 static int sysdata_append_taskname(struct netconsole_target *nt, int offset)
 {
-	return scnprintf(&nt->extradata_complete[offset],
+	return scnprintf(&nt->sysdata[offset],
 			 MAX_EXTRADATA_ENTRY_LEN, " taskname=%s\n",
 			 current->comm);
 }
 
 static int sysdata_append_release(struct netconsole_target *nt, int offset)
 {
-	return scnprintf(&nt->extradata_complete[offset],
+	return scnprintf(&nt->sysdata[offset],
 			 MAX_EXTRADATA_ENTRY_LEN, " release=%s\n",
 			 init_utsname()->release);
 }
@@ -1386,46 +1381,36 @@ static int sysdata_append_release(struct netconsole_target *nt, int offset)
 static int sysdata_append_msgid(struct netconsole_target *nt, int offset)
 {
 	wrapping_assign_add(nt->msgcounter, 1);
-	return scnprintf(&nt->extradata_complete[offset],
+	return scnprintf(&nt->sysdata[offset],
 			 MAX_EXTRADATA_ENTRY_LEN, " msgid=%u\n",
 			 nt->msgcounter);
 }
 
 /*
- * prepare_extradata - append sysdata at extradata_complete in runtime
+ * prepare_sysdata - append sysdata in runtime
  * @nt: target to send message to
  */
-static int prepare_extradata(struct netconsole_target *nt)
+static int prepare_sysdata(struct netconsole_target *nt)
 {
-	int extradata_len;
-
-	/* userdata was appended when configfs write helper was called
-	 * by update_userdata().
-	 */
-	extradata_len = nt->userdata_length;
+	int sysdata_len = 0;
 
 	if (!nt->sysdata_fields)
 		goto out;
 
 	if (nt->sysdata_fields & SYSDATA_CPU_NR)
-		extradata_len += sysdata_append_cpu_nr(nt, extradata_len);
+		sysdata_len += sysdata_append_cpu_nr(nt, sysdata_len);
 	if (nt->sysdata_fields & SYSDATA_TASKNAME)
-		extradata_len += sysdata_append_taskname(nt, extradata_len);
+		sysdata_len += sysdata_append_taskname(nt, sysdata_len);
 	if (nt->sysdata_fields & SYSDATA_RELEASE)
-		extradata_len += sysdata_append_release(nt, extradata_len);
+		sysdata_len += sysdata_append_release(nt, sysdata_len);
 	if (nt->sysdata_fields & SYSDATA_MSGID)
-		extradata_len += sysdata_append_msgid(nt, extradata_len);
+		sysdata_len += sysdata_append_msgid(nt, sysdata_len);
 
-	WARN_ON_ONCE(extradata_len >
-		     MAX_EXTRADATA_ENTRY_LEN * MAX_EXTRADATA_ITEMS);
+	WARN_ON_ONCE(sysdata_len >
+		     MAX_EXTRADATA_ENTRY_LEN * MAX_SYSDATA_ITEMS);
 
 out:
-	return extradata_len;
-}
-#else /* CONFIG_NETCONSOLE_DYNAMIC not set */
-static int prepare_extradata(struct netconsole_target *nt)
-{
-	return 0;
+	return sysdata_len;
 }
 #endif	/* CONFIG_NETCONSOLE_DYNAMIC */
 
@@ -1527,11 +1512,13 @@ static void send_msg_no_fragmentation(struct netconsole_target *nt,
 				      int msg_len,
 				      int release_len)
 {
-	const char *extradata = NULL;
+	const char *userdata = NULL;
+	const char *sysdata = NULL;
 	const char *release;
 
 #ifdef CONFIG_NETCONSOLE_DYNAMIC
-	extradata = nt->extradata_complete;
+	userdata = nt->userdata;
+	sysdata = nt->sysdata;
 #endif
 
 	if (release_len) {
@@ -1543,10 +1530,15 @@ static void send_msg_no_fragmentation(struct netconsole_target *nt,
 		memcpy(nt->buf, msg, msg_len);
 	}
 
-	if (extradata)
+	if (userdata)
 		msg_len += scnprintf(&nt->buf[msg_len],
-				     MAX_PRINT_CHUNK - msg_len,
-				     "%s", extradata);
+				     MAX_PRINT_CHUNK - msg_len, "%s",
+				     userdata);
+
+	if (sysdata)
+		msg_len += scnprintf(&nt->buf[msg_len],
+				     MAX_PRINT_CHUNK - msg_len, "%s",
+				     sysdata);
 
 	send_udp(nt, nt->buf, msg_len);
 }
@@ -1560,89 +1552,93 @@ static void append_release(char *buf)
 }
 
 static void send_fragmented_body(struct netconsole_target *nt,
-				 const char *msgbody, int header_len,
-				 int msgbody_len, int extradata_len)
+				 const char *msgbody_ptr, int header_len,
+				 int msgbody_len, int sysdata_len)
 {
-	int sent_extradata, preceding_bytes;
-	const char *extradata = NULL;
-	int body_len, offset = 0;
+	const char *userdata_ptr = NULL;
+	const char *sysdata_ptr = NULL;
+	int data_len, data_sent = 0;
+	int userdata_offset = 0;
+	int sysdata_offset = 0;
+	int msgbody_offset = 0;
+	int userdata_len = 0;
 
 #ifdef CONFIG_NETCONSOLE_DYNAMIC
-	extradata = nt->extradata_complete;
+	userdata_ptr = nt->userdata;
+	sysdata_ptr = nt->sysdata;
+	userdata_len = nt->userdata_length;
 #endif
+	if (WARN_ON_ONCE(!userdata_ptr && userdata_len != 0))
+		return;
 
-	/* body_len represents the number of bytes that will be sent. This is
+	if (WARN_ON_ONCE(!sysdata_ptr && sysdata_len != 0))
+		return;
+
+	/* data_len represents the number of bytes that will be sent. This is
 	 * bigger than MAX_PRINT_CHUNK, thus, it will be split in multiple
 	 * packets
 	 */
-	body_len = msgbody_len + extradata_len;
+	data_len = msgbody_len + userdata_len + sysdata_len;
 
 	/* In each iteration of the while loop below, we send a packet
-	 * containing the header and a portion of the body. The body is
-	 * composed of two parts: msgbody and extradata. We keep track of how
-	 * many bytes have been sent so far using the offset variable, which
-	 * ranges from 0 to the total length of the body.
+	 * containing the header and a portion of the data. The data is
+	 * composed of three parts: msgbody, userdata, and sysdata.
+	 * We keep track of how many bytes have been sent from each part using
+	 * the *_offset variables.
+	 * We keep track of how many bytes have been sent overall using the
+	 * data_sent variable, which ranges from 0 to the total bytes to be
+	 * sent.
 	 */
-	while (offset < body_len) {
-		int this_header = header_len;
-		bool msgbody_written = false;
-		int this_offset = 0;
+	while (data_sent < data_len) {
+		int userdata_left = userdata_len - userdata_offset;
+		int sysdata_left = sysdata_len - sysdata_offset;
+		int msgbody_left = msgbody_len - msgbody_offset;
+		int buf_offset = 0;
 		int this_chunk = 0;
 
-		this_header += scnprintf(nt->buf + this_header,
-					 MAX_PRINT_CHUNK - this_header,
-					 ",ncfrag=%d/%d;", offset,
-					 body_len);
-
-		/* Not all msgbody data has been written yet */
-		if (offset < msgbody_len) {
-			this_chunk = min(msgbody_len - offset,
-					 MAX_PRINT_CHUNK - this_header);
-			if (WARN_ON_ONCE(this_chunk <= 0))
-				return;
-			memcpy(nt->buf + this_header, msgbody + offset,
-			       this_chunk);
-			this_offset += this_chunk;
+		/* header is already populated in nt->buf, just append to it */
+		buf_offset = header_len;
+
+		buf_offset += scnprintf(nt->buf + buf_offset,
+					 MAX_PRINT_CHUNK - buf_offset,
+					 ",ncfrag=%d/%d;", data_sent,
+					 data_len);
+
+		/* append msgbody first */
+		this_chunk = min(msgbody_left, MAX_PRINT_CHUNK - buf_offset);
+		memcpy(nt->buf + buf_offset, msgbody_ptr + msgbody_offset,
+		       this_chunk);
+		msgbody_offset += this_chunk;
+		buf_offset += this_chunk;
+		data_sent += this_chunk;
+
+		/* after msgbody, append userdata */
+		if (userdata_ptr && userdata_left) {
+			this_chunk = min(userdata_left,
+					 MAX_PRINT_CHUNK - buf_offset);
+			memcpy(nt->buf + buf_offset,
+			       userdata_ptr + userdata_offset, this_chunk);
+			userdata_offset += this_chunk;
+			buf_offset += this_chunk;
+			data_sent += this_chunk;
 		}
 
-		/* msgbody was finally written, either in the previous
-		 * messages and/or in the current buf. Time to write
-		 * the extradata.
-		 */
-		msgbody_written |= offset + this_offset >= msgbody_len;
-
-		/* Msg body is fully written and there is pending extradata to
-		 * write, append extradata in this chunk
-		 */
-		if (msgbody_written && offset + this_offset < body_len) {
-			/* Track how much user data was already sent. First
-			 * time here, sent_userdata is zero
-			 */
-			sent_extradata = (offset + this_offset) - msgbody_len;
-			/* offset of bytes used in current buf */
-			preceding_bytes = this_chunk + this_header;
-
-			if (WARN_ON_ONCE(sent_extradata < 0))
-				return;
-
-			this_chunk = min(extradata_len - sent_extradata,
-					 MAX_PRINT_CHUNK - preceding_bytes);
-			if (WARN_ON_ONCE(this_chunk < 0))
-				/* this_chunk could be zero if all the previous
-				 * message used all the buffer. This is not a
-				 * problem, extradata will be sent in the next
-				 * iteration
-				 */
-				return;
-
-			memcpy(nt->buf + this_header + this_offset,
-			       extradata + sent_extradata,
-			       this_chunk);
-			this_offset += this_chunk;
+		/* after userdata, append sysdata */
+		if (sysdata_ptr && sysdata_left) {
+			this_chunk = min(sysdata_left,
+					 MAX_PRINT_CHUNK - buf_offset);
+			memcpy(nt->buf + buf_offset,
+			       sysdata_ptr + sysdata_offset, this_chunk);
+			sysdata_offset += this_chunk;
+			buf_offset += this_chunk;
+			data_sent += this_chunk;
 		}
 
-		send_udp(nt, nt->buf, this_header + this_offset);
-		offset += this_offset;
+		/* if all is good, send the packet out */
+		if (WARN_ON_ONCE(data_sent > data_len))
+			return;
+
+		send_udp(nt, nt->buf, buf_offset);
 	}
 }
 
@@ -1650,7 +1646,7 @@ static void send_msg_fragmented(struct netconsole_target *nt,
 				const char *msg,
 				int msg_len,
 				int release_len,
-				int extradata_len)
+				int sysdata_len)
 {
 	int header_len, msgbody_len;
 	const char *msgbody;
@@ -1679,7 +1675,7 @@ static void send_msg_fragmented(struct netconsole_target *nt,
 	 * will be replaced
 	 */
 	send_fragmented_body(nt, msgbody, header_len, msgbody_len,
-			     extradata_len);
+			     sysdata_len);
 }
 
 /**
@@ -1695,19 +1691,22 @@ static void send_msg_fragmented(struct netconsole_target *nt,
 static void send_ext_msg_udp(struct netconsole_target *nt, const char *msg,
 			     int msg_len)
 {
+	int userdata_len = 0;
 	int release_len = 0;
-	int extradata_len;
-
-	extradata_len = prepare_extradata(nt);
+	int sysdata_len = 0;
 
+#ifdef CONFIG_NETCONSOLE_DYNAMIC
+	sysdata_len = prepare_sysdata(nt);
+	userdata_len = nt->userdata_length;
+#endif
 	if (nt->release)
 		release_len = strlen(init_utsname()->release) + 1;
 
-	if (msg_len + release_len + extradata_len <= MAX_PRINT_CHUNK)
+	if (msg_len + release_len + sysdata_len + userdata_len <= MAX_PRINT_CHUNK)
 		return send_msg_no_fragmentation(nt, msg, msg_len, release_len);
 
 	return send_msg_fragmented(nt, msg, msg_len, release_len,
-				   extradata_len);
+				   sysdata_len);
 }
 
 static void write_ext_msg(struct console *con, const char *msg,
@@ -1912,6 +1911,9 @@ fail:
 static void free_param_target(struct netconsole_target *nt)
 {
 	netpoll_cleanup(&nt->np);
+#ifdef	CONFIG_NETCONSOLE_DYNAMIC
+	kfree(nt->userdata);
+#endif
 	kfree(nt);
 }
 
diff --git a/tools/testing/selftests/drivers/net/netcons_overflow.sh b/tools/testing/selftests/drivers/net/netcons_overflow.sh
index 29bad56448a2..06089643b771 100755
--- a/tools/testing/selftests/drivers/net/netcons_overflow.sh
+++ b/tools/testing/selftests/drivers/net/netcons_overflow.sh
@@ -15,7 +15,7 @@ SCRIPTDIR=$(dirname "$(readlink -e "${BASH_SOURCE[0]}")")
 
 source "${SCRIPTDIR}"/lib/sh/lib_netcons.sh
 # This is coming from netconsole code. Check for it in drivers/net/netconsole.c
-MAX_USERDATA_ITEMS=16
+MAX_USERDATA_ITEMS=256
 
 # Function to create userdata entries
 function create_userdata_max_entries() {