[nrf fromlist] settings: Make settings_subsys_init() thread safe

Multiple components may use the settings subsystem, so ensure
settings_subsys_init() is thread safe.

Upstream PR: zephyrproject-rtos/zephyr#54943

Signed-off-by: Stig Bjørlykke <[email protected]>

Author: stig-bjorlykke

subsys/settings/src/settings_init.c

@@ -15,6 +15,7 @@
 #include "settings/settings_file.h"
 #include <zephyr/kernel.h>
 
+extern struct k_mutex settings_lock;
 
 bool settings_subsys_initialized;
 
@@ -27,17 +28,19 @@ int settings_subsys_init(void)
 
 	int err = 0;
 
-	if (settings_subsys_initialized) {
-		return 0;
-	}
+	k_mutex_lock(&settings_lock, K_FOREVER);
 
-	settings_init();
+	if (!settings_subsys_initialized) {
+		settings_init();
 
-	err = settings_backend_init(); /* func rises kernel panic once error */
+		err = settings_backend_init(); /* func rises kernel panic once error */
 
-	if (!err) {
-		settings_subsys_initialized = true;
+		if (!err) {
+			settings_subsys_initialized = true;
+		}
 	}
 
+	k_mutex_unlock(&settings_lock);
+
 	return err;
 }