linux-kernel - [PATCH 3/6] samples/damon/mtier: support boot time enable setup

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Message-Id: <20250706193207.39810-4-sj@kernel.org>
Date: Sun,  6 Jul 2025 12:32:04 -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,
	stable@...r.kernel.org
Subject: [PATCH 3/6] samples/damon/mtier: support boot time enable setup

If 'enable' parameter of the 'mtier' 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: 82a08bde3cf7 ("samples/damon: implement a DAMON module for memory tiering")
Cc: stable@...r.kernel.org
Signed-off-by: SeongJae Park <sj@...nel.org>
---
 samples/damon/mtier.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/samples/damon/mtier.c b/samples/damon/mtier.c
index 97892ade7f31..20c3102242ec 100644
--- a/samples/damon/mtier.c
+++ b/samples/damon/mtier.c
@@ -157,6 +157,8 @@ static void damon_sample_mtier_stop(void)
 	damon_destroy_ctx(ctxs[1]);
 }
 
+static bool init_called;
+
 static int damon_sample_mtier_enable_store(
 		const char *val, const struct kernel_param *kp)
 {
@@ -170,6 +172,9 @@ static int damon_sample_mtier_enable_store(
 	if (enable == enabled)
 		return 0;
 
+	if (!init_called)
+		return 0;
+
 	if (enable) {
 		err = damon_sample_mtier_start();
 		if (err)
@@ -182,6 +187,14 @@ static int damon_sample_mtier_enable_store(
 
 static int __init damon_sample_mtier_init(void)
 {
+	int err = 0;
+
+	init_called = true;
+	if (enable) {
+		err = damon_sample_mtier_start();
+		if (err)
+			enable = false;
+	}
 	return 0;
 }
 
-- 
2.39.5