Merge branch 'netconsole-optimize-console-registration-and-improve-testing'

Breno Leitao says:

====================
netconsole: Optimize console registration and improve testing

During performance analysis of console subsystem latency, I discovered that
netconsole registers console handlers even when no active targets exist.
These orphaned console handlers are invoked on every printk() call, get
the lock, iterate through empty target lists, and consume CPU cycles
without performing any useful work.

This patch series addresses the inefficiency by:

1. Implementing dynamic console registration/unregistration based on target
   availability, ensuring console handlers are only active when needed
2. Adding automatic cleanup of unused console registrations when targets
   are disabled or removed
3. Extending the selftest suite to cover non-extended console format,
   which was previously untested

The optimization reduces printk() overhead by eliminating unnecessary
function calls and list traversals when netconsole targets are not
configured, improving overall system performance during heavy logging
scenarios.

v2: https://lore.kernel.org/20250602-netcons_ext-v2-0-ef88d999326d@debian.org
v1: https://lore.kernel.org/20250528-netcons_ext-v1-1-69f71e404e00@debian.org
====================

Link: https://patch.msgid.link/20250609-netcons_ext-v3-0-5336fa670326@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 112 insertions, 32 deletions

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 4289ccd3e41b..21077aff061c 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -86,10 +86,10 @@ static DEFINE_SPINLOCK(target_list_lock);
 static DEFINE_MUTEX(target_cleanup_list_lock);
 
 /*
- * Console driver for extended netconsoles.  Registered on the first use to
- * avoid unnecessarily enabling ext message formatting.
+ * Console driver for netconsoles.  Register only consoles that have
+ * an associated target of the same type.
  */
-static struct console netconsole_ext;
+static struct console netconsole_ext, netconsole;
 
 struct netconsole_target_stats  {
 	u64_stats_t xmit_drop_count;
@@ -97,6 +97,11 @@ struct netconsole_target_stats  {
 	struct u64_stats_sync syncp;
 };
 
+enum console_type {
+	CONS_BASIC = BIT(0),
+	CONS_EXTENDED = BIT(1),
+};
+
 /* Features enabled in sysdata. Contrary to userdata, this data is populated by
  * the kernel. The fields are designed as bitwise flags, allowing multiple
  * features to be set in sysdata_fields.
@@ -455,6 +460,33 @@ static ssize_t sysdata_release_enabled_show(struct config_item *item,
 	return sysfs_emit(buf, "%d\n", release_enabled);
 }
 
+/* Iterate in the list of target, and make sure we don't have any console
+ * register without targets of the same type
+ */
+static void unregister_netcons_consoles(void)
+{
+	struct netconsole_target *nt;
+	u32 console_type_needed = 0;
+	unsigned long flags;
+
+	spin_lock_irqsave(&target_list_lock, flags);
+	list_for_each_entry(nt, &target_list, list) {
+		if (nt->extended)
+			console_type_needed |= CONS_EXTENDED;
+		else
+			console_type_needed |= CONS_BASIC;
+	}
+	spin_unlock_irqrestore(&target_list_lock, flags);
+
+	if (!(console_type_needed & CONS_EXTENDED) &&
+	    console_is_registered(&netconsole_ext))
+		unregister_console(&netconsole_ext);
+
+	if (!(console_type_needed & CONS_BASIC) &&
+	    console_is_registered(&netconsole))
+		unregister_console(&netconsole);
+}
+
 /*
  * This one is special -- targets created through the configfs interface
  * are not enabled (and the corresponding netpoll activated) by default.
@@ -488,8 +520,18 @@ static ssize_t enabled_store(struct config_item *item,
 			goto out_unlock;
 		}
 
-		if (nt->extended && !console_is_registered(&netconsole_ext))
+		if (nt->extended && !console_is_registered(&netconsole_ext)) {
+			netconsole_ext.flags |= CON_ENABLED;
 			register_console(&netconsole_ext);
+		}
+
+		/* User might be enabling the basic format target for the very
+		 * first time, make sure the console is registered.
+		 */
+		if (!nt->extended && !console_is_registered(&netconsole)) {
+			netconsole.flags |= CON_ENABLED;
+			register_console(&netconsole);
+		}
 
 		/*
 		 * Skip netpoll_parse_options() -- all the attributes are
@@ -517,6 +559,10 @@ static ssize_t enabled_store(struct config_item *item,
 		list_move(&nt->list, &target_cleanup_list);
 		spin_unlock_irqrestore(&target_list_lock, flags);
 		mutex_unlock(&target_cleanup_list_lock);
+		/* Unregister consoles, whose the last target of that type got
+		 * disabled.
+		 */
+		unregister_netcons_consoles();
 	}
 
 	ret = strnlen(buf, count);
@@ -1691,8 +1737,8 @@ static int __init init_netconsole(void)
 {
 	int err;
 	struct netconsole_target *nt, *tmp;
+	u32 console_type_needed = 0;
 	unsigned int count = 0;
-	bool extended = false;
 	unsigned long flags;
 	char *target_config;
 	char *input = config;
@@ -1708,9 +1754,10 @@ static int __init init_netconsole(void)
 			}
 			/* Dump existing printks when we register */
 			if (nt->extended) {
-				extended = true;
+				console_type_needed |= CONS_EXTENDED;
 				netconsole_ext.flags |= CON_PRINTBUFFER;
 			} else {
+				console_type_needed |= CONS_BASIC;
 				netconsole.flags |= CON_PRINTBUFFER;
 			}
 
@@ -1729,9 +1776,10 @@ static int __init init_netconsole(void)
 	if (err)
 		goto undonotifier;
 
-	if (extended)
+	if (console_type_needed & CONS_EXTENDED)
 		register_console(&netconsole_ext);
-	register_console(&netconsole);
+	if (console_type_needed & CONS_BASIC)
+		register_console(&netconsole);
 	pr_info("network logging started\n");
 
 	return err;
@@ -1761,7 +1809,8 @@ static void __exit cleanup_netconsole(void)
 
 	if (console_is_registered(&netconsole_ext))
 		unregister_console(&netconsole_ext);
-	unregister_console(&netconsole);
+	if (console_is_registered(&netconsole))
+		unregister_console(&netconsole);
 	dynamic_netconsole_exit();
 	unregister_netdevice_notifier(&netconsole_netdev_notifier);
 
diff --git a/tools/testing/selftests/drivers/net/lib/sh/lib_netcons.sh b/tools/testing/selftests/drivers/net/lib/sh/lib_netcons.sh
index 29b01b8e2215..71a5a8b1712c 100644
--- a/tools/testing/selftests/drivers/net/lib/sh/lib_netcons.sh
+++ b/tools/testing/selftests/drivers/net/lib/sh/lib_netcons.sh
@@ -95,6 +95,8 @@ function set_network() {
 }
 
 function create_dynamic_target() {
+	local FORMAT=${1:-"extended"}
+
 	DSTMAC=$(ip netns exec "${NAMESPACE}" \
 		 ip link show "${DSTIF}" | awk '/ether/ {print $2}')
 
@@ -106,6 +108,16 @@ function create_dynamic_target() {
 	echo "${DSTMAC}" > "${NETCONS_PATH}"/remote_mac
 	echo "${SRCIF}" > "${NETCONS_PATH}"/dev_name
 
+	if [ "${FORMAT}" == "basic" ]
+	then
+		# Basic target does not support release
+		echo 0 > "${NETCONS_PATH}"/release
+		echo 0 > "${NETCONS_PATH}"/extended
+	elif [ "${FORMAT}" == "extended" ]
+	then
+		echo 1 > "${NETCONS_PATH}"/extended
+	fi
+
 	echo 1 > "${NETCONS_PATH}"/enabled
 }
 
@@ -159,6 +171,7 @@ function listen_port_and_save_to() {
 
 function validate_result() {
 	local TMPFILENAME="$1"
+	local FORMAT=${2:-"extended"}
 
 	# TMPFILENAME will contain something like:
 	# 6.11.1-0_fbk0_rc13_509_g30d75cea12f7,13,1822,115075213798,-;netconsole selftest: netcons_gtJHM
@@ -176,16 +189,20 @@ function validate_result() {
 		exit "${ksft_fail}"
 	fi
 
-	if ! grep -q "${USERDATA_KEY}=${USERDATA_VALUE}" "${TMPFILENAME}"; then
-		echo "FAIL: ${USERDATA_KEY}=${USERDATA_VALUE} not found in ${TMPFILENAME}" >&2
-		cat "${TMPFILENAME}" >&2
-		exit "${ksft_fail}"
+	# userdata is not supported on basic format target,
+	# thus, do not validate it.
+	if [ "${FORMAT}" != "basic" ];
+	then
+		if ! grep -q "${USERDATA_KEY}=${USERDATA_VALUE}" "${TMPFILENAME}"; then
+			echo "FAIL: ${USERDATA_KEY}=${USERDATA_VALUE} not found in ${TMPFILENAME}" >&2
+			cat "${TMPFILENAME}" >&2
+			exit "${ksft_fail}"
+		fi
 	fi
 
 	# Delete the file once it is validated, otherwise keep it
 	# for debugging purposes
 	rm "${TMPFILENAME}"
-	exit "${ksft_pass}"
 }
 
 function check_for_dependencies() {
diff --git a/tools/testing/selftests/drivers/net/netcons_basic.sh b/tools/testing/selftests/drivers/net/netcons_basic.sh
index fe765da498e8..40a6ac6191b8 100755
--- a/tools/testing/selftests/drivers/net/netcons_basic.sh
+++ b/tools/testing/selftests/drivers/net/netcons_basic.sh
@@ -32,21 +32,35 @@ check_for_dependencies
 echo "6 5" > /proc/sys/kernel/printk
 # Remove the namespace, interfaces and netconsole target on exit
 trap cleanup EXIT
-# Create one namespace and two interfaces
-set_network
-# Create a dynamic target for netconsole
-create_dynamic_target
-# Set userdata "key" with the "value" value
-set_user_data
-# Listed for netconsole port inside the namespace and destination interface
-listen_port_and_save_to "${OUTPUT_FILE}" &
-# Wait for socat to start and listen to the port.
-wait_local_port_listen "${NAMESPACE}" "${PORT}" udp
-# Send the message
-echo "${MSG}: ${TARGET}" > /dev/kmsg
-# Wait until socat saves the file to disk
-busywait "${BUSYWAIT_TIMEOUT}" test -s "${OUTPUT_FILE}"
-
-# Make sure the message was received in the dst part
-# and exit
-validate_result "${OUTPUT_FILE}"
+
+# Run the test twice, with different format modes
+for FORMAT in "basic" "extended"
+do
+	echo "Running with target mode: ${FORMAT}"
+	# Create one namespace and two interfaces
+	set_network
+	# Create a dynamic target for netconsole
+	create_dynamic_target "${FORMAT}"
+	# Only set userdata for extended format
+	if [ "$FORMAT" == "extended" ]
+	then
+		# Set userdata "key" with the "value" value
+		set_user_data
+	fi
+	# Listed for netconsole port inside the namespace and destination interface
+	listen_port_and_save_to "${OUTPUT_FILE}" &
+	# Wait for socat to start and listen to the port.
+	wait_local_port_listen "${NAMESPACE}" "${PORT}" udp
+	# Send the message
+	echo "${MSG}: ${TARGET}" > /dev/kmsg
+	# Wait until socat saves the file to disk
+	busywait "${BUSYWAIT_TIMEOUT}" test -s "${OUTPUT_FILE}"
+
+	# Make sure the message was received in the dst part
+	# and exit
+	validate_result "${OUTPUT_FILE}" "${FORMAT}"
+	cleanup
+done
+
+trap - EXIT
+exit "${ksft_pass}"