selftest/damon: add a test for duplicate context dirs creation

Patch series "mm/damon: minor fixes and cleanups".

This patchset contains minor fixes and cleanups for DAMON including

- selftest for a bug we found before (Patch 1), 
- fix of region holes in vaddr corner case and a kunit test for it
  (Patches 2 and 3), and
- documents/Kconfig updates for title wordsmithing (Patch 4) and more
  aggressive DAMON debugfs interface deprecation announcement
  (Patches 5-7).


This patch (of 7):

Commit d26f6070 ("mm/damon/dbgfs: avoid duplicate context directory
creation") fixes a bug which could result in memory leak and DAMON
disablement.  This commit adds a selftest for verifying the fix and avoid
regression.

Link: https://lkml.kernel.org/r/20220909202901.57977-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20220909202901.57977-2-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Yun Levi <ppbuk5246@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/damon/Makefile

@@ -6,6 +6,7 @@ TEST_GEN_FILES += huge_count_read_write
 TEST_FILES = _chk_dependency.sh _debugfs_common.sh
 TEST_PROGS = debugfs_attrs.sh debugfs_schemes.sh debugfs_target_ids.sh
 TEST_PROGS += debugfs_empty_targets.sh debugfs_huge_count_read_write.sh
+TEST_PROGS += debugfs_duplicate_context_creation.sh
 TEST_PROGS += sysfs.sh
 
 include ../lib.mk

tools/testing/selftests/damon/debugfs_duplicate_context_creation.sh

+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+source _debugfs_common.sh
+
+# Test duplicated context creation
+# ================================
+
+if ! echo foo > "$DBGFS/mk_contexts"
+then
+	echo "context creation failed"
+	exit 1
+fi
+
+if echo foo > "$DBGFS/mk_contexts"
+then
+	echo "duplicate context creation success"
+	exit 1
+fi
+
+if ! echo foo > "$DBGFS/rm_contexts"
+then
+	echo "context deletion failed"
+	exit 1
+fi
+
+exit 0