[RFC PATCH 02/11] selftests:lib: add new test for counters

[Shuah Khan]

Add a new selftest for testing counter and counter_atomic counters
api. This test load test_counters test modules and unloads.

The test module runs tests and prints results in dmesg.

There are a number of atomic_t usages in the kernel where atomic_t api
is used strictly for counting and not for managing object lifetime. In
some cases, atomic_t might not even be needed.

The purpose of these counters is twofold: 1. clearly differentiate
atomic_t counters from atomic_t usages that guard object lifetimes,
hence prone to overflow and underflow errors. It allows tools that scan
for underflow and overflow on atomic_t usages to detect overflow and
underflows to scan just the cases that are prone to errors. 2. provides
non-atomic counters for cases where atomic isn't necessary.

Simple atomic and non-atomic counters api provides interfaces for simple
atomic and non-atomic counters that just count, and don't guard resource
lifetimes. Counters will wrap around to 0 when it overflows and should
not be used to guard resource lifetimes, device usage and open counts
that control state changes, and pm states.

Using counter_atomic to guard lifetimes could lead to use-after free
when it overflows and undefined behavior when used to manage state
changes and device usage/open states.

Signed-off-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
---
 MAINTAINERS                                  | 1 +
 tools/testing/selftests/lib/Makefile         | 1 +
 tools/testing/selftests/lib/config           | 1 +
 tools/testing/selftests/lib/test_counters.sh | 5 +++++
 4 files changed, 8 insertions(+)
 create mode 100755 tools/testing/selftests/lib/test_counters.sh

diff --git a/MAINTAINERS b/MAINTAINERS
index 1d3abcfa76ab..fc802ef0ee95 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15847,6 +15847,7 @@ L:	linux-kernel@xxxxxxxxxxxxxxx
 S:	Maintained
 F:	include/linux/counters.h
 F:	lib/test_counters.c
+F:	tools/testing/selftests/lib/test_counters.sh
 
 SIMPLE FIRMWARE INTERFACE (SFI)
 S:	Obsolete
diff --git a/tools/testing/selftests/lib/Makefile b/tools/testing/selftests/lib/Makefile
index a105f094676e..e8960d7934e2 100644
--- a/tools/testing/selftests/lib/Makefile
+++ b/tools/testing/selftests/lib/Makefile
@@ -5,5 +5,6 @@
 all:
 
 TEST_PROGS := printf.sh bitmap.sh prime_numbers.sh strscpy.sh
+TEST_PROGS += test_counters.sh
 
 include ../lib.mk
diff --git a/tools/testing/selftests/lib/config b/tools/testing/selftests/lib/config
index b80ee3f6e265..6ed25024d371 100644
--- a/tools/testing/selftests/lib/config
+++ b/tools/testing/selftests/lib/config
@@ -3,3 +3,4 @@ CONFIG_TEST_BITMAP=m
 CONFIG_PRIME_NUMBERS=m
 CONFIG_TEST_STRSCPY=m
 CONFIG_TEST_BITOPS=m
+CONFIG_TEST_COUNTERS=m
diff --git a/tools/testing/selftests/lib/test_counters.sh b/tools/testing/selftests/lib/test_counters.sh
new file mode 100755
index 000000000000..d1a130190e3f
--- /dev/null
+++ b/tools/testing/selftests/lib/test_counters.sh
@@ -0,0 +1,5 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# Tests the Simple Atomic and Non-atomic Counters interfaces using
+# test_counters kernel module
+$(dirname $0)/../kselftest/module.sh "test_counters" test_counters
-- 
2.25.1