@@ -115,3 +115,12 @@ Decrements sequence number and doesn't return the new value. ::
seqnum32_dec() --> atomic_dec()
seqnum64_dec() --> atomic64_dec()
+
+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.
+Please find selftest: testing/selftests/lib/test_seqnum_ops.sh
+Please check dmesg for results after running test_seqnum_ops.sh.
@@ -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
@@ -28,6 +28,8 @@
*
* Reference and API guide:
* Documentation/core-api/seqnum_ops.rst for more information.
+ * lib/test_seqnum_ops.c - example usages
+ * tools/testing/selftests/lib/test_seqnum_ops.sh
*
*/
@@ -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
@@ -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
new file mode 100755
@@ -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
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. There are a number of atomic_t usages in the kernel where atomic_t api is used strictly for counting sequence numbers and other statistical counters and not for managing object lifetime. The purpose of these Sequence Number Ops is to clearly differentiate atomic_t counter usages from atomic_t usages that guard object lifetimes, hence prone to overflow and underflow errors. 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. Sequence Number api provides interfaces for simple atomic_t counter usages that just count, and don't guard resource lifetimes. The seqnum_ops are built on top of atomic_t api, providing a smaller subset of atomic_t interfaces necessary to support atomic_t usages as simple counters. This api has init/set/inc/dec/read and doesn't support other atomic_t ops with the intent to restrict the use of these interfaces as simple counting usages. Sequence Numbers wrap around to INT_MIN when it overflows and should not be used to guard resource lifetimes, device usage and open counts that control state changes, and pm states. Overflowing to INT_MIN is consistent with the atomic_t api, which it is built on top of. Using seqnum 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@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