selftest: netcons: create a torture test

Create a netconsole test that puts a lot of pressure on the netconsole
list manipulation. Do it by creating dynamic targets and deleting
targets while messages are being sent. Also put interface down while the
messages are being sent, as creating parallel targets.

The code launches three background jobs on distinct schedules:

 * Toggle netcons target every 30 iterations
 * create and delete random_target every 50 iterations
 * toggle iface every 70 iterations

This creates multiple concurrency sources that interact with netconsole
states. This is good practice to simulate stress, and exercise netpoll
and netconsole locks.

This test already found an issue as reported in [1]

Link: https://lore.kernel.org/all/20250901-netpoll_memleak-v1-1-34a181977dfc@debian.org/ [1]
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Andre Carvalho <asantostc@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20251107-netconsole_torture-v10-3-749227b55f63@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: leitao

tools/testing/selftests/drivers/net/Makefile

@@ -18,6 +18,7 @@ TEST_PROGS := \
 	netcons_fragmented_msg.sh \
 	netcons_overflow.sh \
 	netcons_sysdata.sh \
+	netcons_torture.sh \
 	netpoll_basic.py \
 	ping.py \
 	psp.py \

tools/testing/selftests/drivers/net/netcons_torture.sh

@@ -0,0 +1,130 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: GPL-2.0
+
+# Repeatedly send kernel messages, toggles netconsole targets on and off,
+# creates and deletes targets in parallel, and toggles the source interface to
+# simulate stress conditions.
+#
+# This test aims to verify the robustness of netconsole under dynamic
+# configurations and concurrent operations.
+#
+# The major goal is to run this test with LOCKDEP, Kmemleak and KASAN to make
+# sure no issues is reported.
+#
+# Author: Breno Leitao <leitao@debian.org>
+
+set -euo pipefail
+
+SCRIPTDIR=$(dirname "$(readlink -e "${BASH_SOURCE[0]}")")
+
+source "${SCRIPTDIR}"/lib/sh/lib_netcons.sh
+
+# Number of times the main loop run
+ITERATIONS=${1:-150}
+
+# Only test extended format
+FORMAT="extended"
+# And ipv6 only
+IP_VERSION="ipv6"
+
+# Create, enable and delete some targets.
+create_and_delete_random_target() {
+	COUNT=2
+	RND_PREFIX=$(mktemp -u netcons_rnd_XXXX_)
+
+	if [ -d "${NETCONS_CONFIGFS}/${RND_PREFIX}${COUNT}"  ] || \
+	   [ -d "${NETCONS_CONFIGFS}/${RND_PREFIX}0" ]; then
+		echo "Function didn't finish yet, skipping it." >&2
+		return
+	fi
+
+	# enable COUNT targets
+	for i in $(seq ${COUNT})
+	do
+		RND_TARGET="${RND_PREFIX}"${i}
+		RND_TARGET_PATH="${NETCONS_CONFIGFS}"/"${RND_TARGET}"
+
+		# Basic population so the target can come up
+		_create_dynamic_target "${FORMAT}" "${RND_TARGET_PATH}"
+	done
+
+	echo "netconsole selftest: ${COUNT} additional targets were created" > /dev/kmsg
+	# disable them all
+	for i in $(seq ${COUNT})
+	do
+		RND_TARGET="${RND_PREFIX}"${i}
+		RND_TARGET_PATH="${NETCONS_CONFIGFS}"/"${RND_TARGET}"
+		if [[ $(cat "${RND_TARGET_PATH}/enabled") -eq 1 ]]
+		then
+			echo 0 > "${RND_TARGET_PATH}"/enabled
+		fi
+		rmdir "${RND_TARGET_PATH}"
+	done
+}
+
+# Disable and enable the target mid-air, while messages
+# are being transmitted.
+toggle_netcons_target() {
+	for i in $(seq 2)
+	do
+		if [ ! -d "${NETCONS_PATH}" ]
+		then
+			break
+		fi
+		echo 0 > "${NETCONS_PATH}"/enabled 2> /dev/null || true
+		# Try to enable a bit harder, given it might fail to enable
+		# Write to `enabled` might fail depending on the lock, which is
+		# highly contentious here
+		for _ in $(seq 5)
+		do
+			echo 1 > "${NETCONS_PATH}"/enabled 2> /dev/null || true
+		done
+	done
+}
+
+toggle_iface(){
+	ip link set "${SRCIF}" down
+	ip link set "${SRCIF}" up
+}
+
+# Start here
+
+modprobe netdevsim 2> /dev/null || true
+modprobe netconsole 2> /dev/null || true
+
+# Check for basic system dependency and exit if not found
+check_for_dependencies
+# Set current loglevel to KERN_INFO(6), and default to KERN_NOTICE(5)
+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 "${IP_VERSION}"
+# Create a dynamic target for netconsole
+create_dynamic_target "${FORMAT}"
+
+for i in $(seq "$ITERATIONS")
+do
+	for _ in $(seq 10)
+	do
+		echo "${MSG}: ${TARGET} ${i}" > /dev/kmsg
+	done
+	wait
+
+	if (( i % 30 == 0 )); then
+		toggle_netcons_target &
+	fi
+
+	if (( i % 50 == 0 )); then
+		# create some targets, enable them, send msg and disable
+		# all in a parallel thread
+		create_and_delete_random_target &
+	fi
+
+	if (( i % 70 == 0 )); then
+		toggle_iface &
+	fi
+done
+wait
+
+exit "${EXIT_STATUS}"