[PATCH] selftests/damon: test removed scheme sysfs dir access bug

[SeongJae Park <sj@kernel.org>]

A DAMON sysfs user could start DAMON with a scheme, remove the sysfs
directory for the scheme, and then ask stats or schemes tried regions
update.  The related logic were not aware of the already removed
directory situation, so it was able to results in invalid memory
accesses.  The fix has made with commit 8468b486612c
("mm/damon/sysfs-schemes: skip stats update if the scheme directory is
removed"), though.  Add a selftest to avoid such kind of bugs be
introduced again.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 tools/testing/selftests/damon/Makefile        |  2 +-
 .../damon/sysfs_update_removed_scheme_dir.sh  | 58 +++++++++++++++++++
 2 files changed, 59 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/damon/sysfs_update_removed_scheme_dir.sh

diff --git a/tools/testing/selftests/damon/Makefile b/tools/testing/selftests/damon/Makefile
index 838a8e49f77b..b71247ba7196 100644
--- a/tools/testing/selftests/damon/Makefile
+++ b/tools/testing/selftests/damon/Makefile
@@ -8,7 +8,7 @@ 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 += debugfs_rm_non_contexts.sh
-TEST_PROGS += sysfs.sh
+TEST_PROGS += sysfs.sh sysfs_update_removed_scheme_dir.sh
 TEST_PROGS += reclaim.sh lru_sort.sh
 
 include ../lib.mk
diff --git a/tools/testing/selftests/damon/sysfs_update_removed_scheme_dir.sh b/tools/testing/selftests/damon/sysfs_update_removed_scheme_dir.sh
new file mode 100644
index 000000000000..ade35576e748
--- /dev/null
+++ b/tools/testing/selftests/damon/sysfs_update_removed_scheme_dir.sh
@@ -0,0 +1,58 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+
+if [ $EUID -ne 0 ]
+then
+	echo "Run as root"
+	exit $ksft_skip
+fi
+
+damon_sysfs="/sys/kernel/mm/damon/admin"
+if [ ! -d "$damon_sysfs" ]
+then
+	echo "damon sysfs not found"
+	exit $ksft_skip
+fi
+
+# clear log
+dmesg -C
+
+# start DAMON with a scheme
+echo 1 > "$damon_sysfs/kdamonds/nr_kdamonds"
+echo 1 > "$damon_sysfs/kdamonds/0/contexts/nr_contexts"
+echo "vaddr" > "$damon_sysfs/kdamonds/0/contexts/0/operations"
+echo 1 > "$damon_sysfs/kdamonds/0/contexts/0/targets/nr_targets"
+echo $$ > "$damon_sysfs/kdamonds/0/contexts/0/targets/0/pid_target"
+echo 1 > "$damon_sysfs/kdamonds/0/contexts/0/schemes/nr_schemes"
+scheme_dir="$damon_sysfs/kdamonds/0/contexts/0/schemes/0"
+echo 4096000 > "$scheme_dir/access_pattern/sz/max"
+echo 20 > "$scheme_dir/access_pattern/nr_accesses/max"
+echo 1024 > "$scheme_dir/access_pattern/age/max"
+echo "on" > "$damon_sysfs/kdamonds/0/state"
+sleep 0.3
+
+# remove scheme sysfs dir
+echo 0 > "$damon_sysfs/kdamonds/0/contexts/0/schemes/nr_schemes"
+
+# try to update stat of already removed scheme sysfs dir
+echo "update_schemes_stats" > "$damon_sysfs/kdamonds/0/state"
+if dmesg | grep -q BUG
+then
+	echo "update_schemes_stats triggers a kernel bug"
+	dmesg
+	exit 1
+fi
+
+# try to update tried regions of already removed scheme sysfs dir
+echo "update_schemes_tried_regions" > "$damon_sysfs/kdamonds/0/state"
+if dmesg | grep -q BUG
+then
+	echo "update_schemes_tried_regions triggers a kernel bug"
+	dmesg
+	exit 1
+fi
+
+echo "off" > "$damon_sysfs/kdamonds/0/state"
-- 
2.25.1