[PATCH v2 02/13] selftests: lib:test_seqnum_ops: add new test for seqnum_ops

[Shuah Khan <skhan@linuxfoundation.org>]

Add a new selftest for testing seqnum_ops. This test loads test_seqnum_ops
test module and unloads it. The test module runs tests and prints results
to dmesg.

Sequence Number api provides interfaces for unsigned atomic up counters
leveraging atomic_t and atomic64_t ops underneath.

There are a number of atomic_t usages in the kernel where atomic_t api
is used for counting sequence numbers and other statistical counters.
Several of these usages, convert atomic_read() and atomic_inc_return()
return values to unsigned. Introducing sequence number ops supports
these use-cases with a standard core-api.

The atomic_t api provides a wide range of atomic operations as a base
api to implement atomic counters, bitops, spinlock interfaces. The usages
also evolved into being used for resource lifetimes and state management.
The refcount_t api was introduced to address resource lifetime problems
related to atomic_t wrapping. There is a large overlap between the
atomic_t api used for resource lifetimes and just counters, stats, and
sequence numbers. It has become difficult to differentiate between the
atomic_t usages that should be converted to refcount_t and the ones that
can be left alone. Introducing seqnum_ops to wrap the usages that are
stats, counters, sequence numbers makes it easier for 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.

In addition, to supporting sequence number use-cases, Sequence Number Ops
helps differentiate atomic_t counter usages from atomic_t usages that guard
object lifetimes, hence prone to overflow and underflow errors from up
counting use-cases.

Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
---
 Documentation/core-api/seqnum_ops.rst          |  9 +++++++++
 MAINTAINERS                                    |  1 +
 include/linux/seqnum_ops.h                     |  2 ++
 tools/testing/selftests/lib/Makefile           |  1 +
 tools/testing/selftests/lib/config             |  1 +
 tools/testing/selftests/lib/test_seqnum_ops.sh | 10 ++++++++++
 6 files changed, 24 insertions(+)
 create mode 100755 tools/testing/selftests/lib/test_seqnum_ops.sh

diff --git a/Documentation/core-api/seqnum_ops.rst b/Documentation/core-api/seqnum_ops.rst
index 10b775a9ac05..f66d796b148e 100644
--- a/Documentation/core-api/seqnum_ops.rst
+++ b/Documentation/core-api/seqnum_ops.rst
@@ -78,3 +78,12 @@ Fetched and returns current sequence number value. ::
 
         seqnum32_fetch() --> (u32) atomic_add_return(0, seqnum)
         seqnum64_fetch() --> (u64) atomic64_add_return(0, seqnum)
+
+Where are the seqnum_ops and how to use and test them?
+------------------------------------------------------
+
+.. kernel-doc:: include/linux/seqnum_ops.h
+
+Please see lib/test_seqnum_ops.c for examples usages and test module.
+Please find selftest: testing/selftests/lib/test_seqnum_ops.sh
+Please check dmesg for results after running test_seqnum_ops.sh.
diff --git a/MAINTAINERS b/MAINTAINERS
index c83a6f05610b..e6ae131836a5 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15983,6 +15983,7 @@ L:	linux-kernel@vger.kernel.org
 S:	Maintained
 F:	include/linux/seqnum_ops.h
 F:	lib/test_seqnum_ops.c
+F:	tools/testing/selftests/lib/test_seqnum_ops.sh
 
 SIMPLE FIRMWARE INTERFACE (SFI)
 S:	Obsolete
diff --git a/include/linux/seqnum_ops.h b/include/linux/seqnum_ops.h
index 17d327b78050..bbf724f21e03 100644
--- a/include/linux/seqnum_ops.h
+++ b/include/linux/seqnum_ops.h
@@ -19,6 +19,8 @@
  *
  * Reference and API guide:
  *	Documentation/core-api/seqnum_ops.rst for more information.
+ *	lib/test_seqnum_ops.c - example usages and test module
+ *	tools/testing/selftests/lib/test_seqnum_ops.sh
  */
 
 #ifndef __LINUX_SEQNUM_OPS_H
diff --git a/tools/testing/selftests/lib/Makefile b/tools/testing/selftests/lib/Makefile
index a105f094676e..1818444f0e97 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_seqnum_ops.sh
 
 include ../lib.mk
diff --git a/tools/testing/selftests/lib/config b/tools/testing/selftests/lib/config
index b80ee3f6e265..674ed2a2ac82 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_SEQNUM_OPS=m
diff --git a/tools/testing/selftests/lib/test_seqnum_ops.sh b/tools/testing/selftests/lib/test_seqnum_ops.sh
new file mode 100755
index 000000000000..fdce16b220ba
--- /dev/null
+++ b/tools/testing/selftests/lib/test_seqnum_ops.sh
@@ -0,0 +1,10 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (c) 2020 Shuah Khan <skhan@linuxfoundation.org>
+# Copyright (c) 2020 The Linux Foundation
+#
+# Tests the Sequence Number Ops interfaces using test_seqnum_ops
+# kernel module
+#
+$(dirname $0)/../kselftest/module.sh "test_seqnum_ops" test_seqnum_ops
-- 
2.27.0