[PATCH 2/6] samples/damon/prcl: fix boot time enable crash

[SeongJae Park <sj@kernel.org>]

If 'enable' parameter of the 'prcl' 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: 2aca254620a8 ("samples/damon: introduce a skeleton of a smaple DAMON module for proactive reclamation")
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 samples/damon/prcl.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/samples/damon/prcl.c b/samples/damon/prcl.c
index 5597e6a08ab2..f04a18a8626a 100644
--- a/samples/damon/prcl.c
+++ b/samples/damon/prcl.c
@@ -109,6 +109,8 @@ static void damon_sample_prcl_stop(void)
 		put_pid(target_pidp);
 }
 
+static bool init_called;
+
 static int damon_sample_prcl_enable_store(
 		const char *val, const struct kernel_param *kp)
 {
@@ -122,6 +124,9 @@ static int damon_sample_prcl_enable_store(
 	if (enable == enabled)
 		return 0;
 
+	if (!init_called)
+		return 0;
+
 	if (enable) {
 		err = damon_sample_prcl_start();
 		if (err)
@@ -134,6 +139,14 @@ static int damon_sample_prcl_enable_store(
 
 static int __init damon_sample_prcl_init(void)
 {
+	int err = 0;
+
+	init_called = true;
+	if (enable) {
+		err = damon_sample_prcl_start();
+		if (err)
+			enable = false;
+	}
 	return 0;
 }
 
-- 
2.39.5