From d771b7267accbb73c5f40c9fe3515cf401335638 Mon Sep 17 00:00:00 2001
From: SeongJae Park <sj@kernel.org>
Date: Thu, 1 Dec 2022 17:08:34 +0000
Subject: [PATCH] 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 8468b486612c ("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/20221201170834.62823-1-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.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 838a8e49f77b9a..b71247ba71969b 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 00000000000000..ade35576e74876
--- /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"