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

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Message-Id: <20250706193207.39810-3-sj@kernel.org>
Date: Sun,  6 Jul 2025 12:32:03 -0700
From: SeongJae Park <sj@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: SeongJae Park <sj@...nel.org>,
	damon@...ts.linux.dev,
	kernel-team@...a.com,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [PATCH 2/6] samples/damon/prcl: fix boot time enable crash

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@...nel.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