samples/damon/prcl: fix boot time enable crash

[ Upstream commit 2780505 ]

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.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 2aca254 ("samples/damon: introduce a skeleton of a smaple DAMON module for proactive reclamation")
Signed-off-by: SeongJae Park <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Stable-dep-of: c62cff4 ("samples/damon/mtier: avoid starting DAMON before initialization")
Signed-off-by: Sasha Levin <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: sjp38

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)
 {
@@ -134,6 +136,14 @@ 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;
 }