selftests/damon: test removed scheme sysfs dir access bug

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 8468b48 ("mm/damon/sysfs-schemes: skip stats
update if the scheme directory is removed"), though.  Add a selftest to
prevent such kinds of bugs from being introduced again.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: SeongJae Park <[email protected]>
Cc: Shuah Khan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: sjp38

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

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"