[RFC PATCH 05/20] landlock: Make ruleset deferred free RCU safe

[Justin Suess <utilityemal77@gmail.com>]

Use INIT_RCU_WORK in the landlock deferred free function, ensuring that
deferred ruleset freeing is also RCU safe.

This is important for future consumers who may free a Landlock ruleset
under RCU in subsequent patches.

Signed-off-by: Justin Suess <utilityemal77@gmail.com>
---
 security/landlock/ruleset.c | 9 +++++----
 security/landlock/ruleset.h | 6 +++---
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index 4f0305796165..5845cdc58d0d 100644
--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c
@@ -699,16 +699,17 @@ static void free_ruleset_work(struct work_struct *const work)
 {
 	struct landlock_ruleset *ruleset;
 
-	ruleset = container_of(work, struct landlock_ruleset, work_free);
+	ruleset = container_of(to_rcu_work(work), struct landlock_ruleset,
+			       work_free);
 	free_ruleset(ruleset);
 }
 
-/* Only called by hook_cred_free(). */
+/* Called by deferred ruleset owners that cannot free from their context. */
 void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset)
 {
 	if (ruleset && refcount_dec_and_test(&ruleset->usage)) {
-		INIT_WORK(&ruleset->work_free, free_ruleset_work);
-		schedule_work(&ruleset->work_free);
+		INIT_RCU_WORK(&ruleset->work_free, free_ruleset_work);
+		queue_rcu_work(system_wq, &ruleset->work_free);
 	}
 }
 
diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
index 0facc5cb6555..fbbd1b73476e 100644
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h
@@ -146,13 +146,13 @@ struct landlock_ruleset {
 	struct landlock_hierarchy *hierarchy;
 	union {
 		/**
-		 * @work_free: Enables to free a ruleset within a lockless
-		 * section.  This is only used by
+		 * @work_free: Enables to free a ruleset after an RCU grace
+		 * period from a sleepable context.  This is only used by
 		 * landlock_put_ruleset_deferred() when @usage reaches zero.
 		 * The fields @lock, @usage, @num_rules, @num_layers and
 		 * @access_masks are then unused.
 		 */
-		struct work_struct work_free;
+		struct rcu_work work_free;
 		struct {
 			/**
 			 * @lock: Protects against concurrent modifications of
-- 
2.53.0