If 'enable' parameter of the 'wsse' DAMON sample module is set at boot
time via the kernel command line, memory allocation is tried before the
slab is initialized.  As a result kernel NULL pointer dereference BUG
can happen.  Fix it by checking the initialization status.

Fixes: b757c6cfc696 ("samples/damon/wsse: start and stop DAMON as the user requests")
Cc: stable@vger.kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 samples/damon/wsse.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/samples/damon/wsse.c b/samples/damon/wsse.c
index e20238a249e7..15e2683fe5f3 100644
--- a/samples/damon/wsse.c
+++ b/samples/damon/wsse.c
@@ -89,6 +89,8 @@ static void damon_sample_wsse_stop(void)
 		put_pid(target_pidp);
 }
 
+static bool init_called;
+
 static int damon_sample_wsse_enable_store(
 		const char *val, const struct kernel_param *kp)
 {
@@ -103,6 +105,9 @@ static int damon_sample_wsse_enable_store(
 		return 0;
 
 	if (enable) {
+		if (!init_called)
+			return 0;
+
 		err = damon_sample_wsse_start();
 		if (err)
 			enable = false;
@@ -114,7 +119,15 @@ static int damon_sample_wsse_enable_store(
 
 static int __init damon_sample_wsse_init(void)
 {
-	return 0;
+	int err = 0;
+
+	init_called = true;
+	if (enable) {
+		err = damon_sample_wsse_start();
+		if (err)
+			enable = false;
+	}
+	return err;
 }
 
 module_init(damon_sample_wsse_init);
-- 
2.39.5