rcu: Refactor kvfree_call_rcu() and high-level helpers

Currently a kvfree_call_rcu() takes an offset within a structure as
a second parameter, so a helper such as a kvfree_rcu_arg_2() has to
convert rcu_head and a freed ptr to an offset in order to pass it. That
leads to an extra conversion on macro entry.

Instead of converting, refactor the code in way that a pointer that has
to be freed is passed directly to the kvfree_call_rcu().

This patch does not make any functional change and is transparent to
all kvfree_rcu() users.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Author: urezki

include/linux/rcupdate.h

@@ -1011,8 +1011,7 @@ do {									\
 									\
 	if (___p) {									\
 		BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf)));	\
-		kvfree_call_rcu(&((___p)->rhf), (rcu_callback_t)(unsigned long)		\
-			(offsetof(typeof(*(ptr)), rhf)));				\
+		kvfree_call_rcu(&((___p)->rhf), (void *) (___p));			\
 	}										\
 } while (0)
 
@@ -1021,7 +1020,7 @@ do {								\
 	typeof(ptr) ___p = (ptr);				\
 								\
 	if (___p)						\
-		kvfree_call_rcu(NULL, (rcu_callback_t) (___p));	\
+		kvfree_call_rcu(NULL, (void *) (___p));		\
 } while (0)
 
 /*

include/linux/rcutiny.h

@@ -98,25 +98,25 @@ static inline void synchronize_rcu_expedited(void)
  */
 extern void kvfree(const void *addr);
 
-static inline void __kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
+static inline void __kvfree_call_rcu(struct rcu_head *head, void *ptr)
 {
 	if (head) {
-		call_rcu(head, func);
+		call_rcu(head, (rcu_callback_t) ((void *) head - ptr));
 		return;
 	}
 
 	// kvfree_rcu(one_arg) call.
 	might_sleep();
 	synchronize_rcu();
-	kvfree((void *) func);
+	kvfree(ptr);
 }
 
 #ifdef CONFIG_KASAN_GENERIC
-void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func);
+void kvfree_call_rcu(struct rcu_head *head, void *ptr);
 #else
-static inline void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
+static inline void kvfree_call_rcu(struct rcu_head *head, void *ptr)
 {
-	__kvfree_call_rcu(head, func);
+	__kvfree_call_rcu(head, ptr);
 }
 #endif
 

include/linux/rcutree.h

@@ -33,7 +33,7 @@ static inline void rcu_virt_note_context_switch(void)
 }
 
 void synchronize_rcu_expedited(void);
-void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func);
+void kvfree_call_rcu(struct rcu_head *head, void *ptr);
 
 void rcu_barrier(void);
 bool rcu_eqs_special_set(int cpu);

kernel/rcu/tiny.c

@@ -246,15 +246,12 @@ bool poll_state_synchronize_rcu(unsigned long oldstate)
 EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
 
 #ifdef CONFIG_KASAN_GENERIC
-void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
+void kvfree_call_rcu(struct rcu_head *head, void *ptr)
 {
-	if (head) {
-		void *ptr = (void *) head - (unsigned long) func;
-
+	if (head)
 		kasan_record_aux_stack_noalloc(ptr);
-	}
 
-	__kvfree_call_rcu(head, func);
+	__kvfree_call_rcu(head, ptr);
 }
 EXPORT_SYMBOL_GPL(kvfree_call_rcu);
 #endif

kernel/rcu/tree.c

@@ -3103,8 +3103,8 @@ static void kfree_rcu_work(struct work_struct *work)
 	 * This list is named "Channel 3".
 	 */
 	for (; head; head = next) {
-		unsigned long offset = (unsigned long)head->func;
-		void *ptr = (void *)head - offset;
+		void *ptr = (void *) head->func;
+		unsigned long offset = (void *) head - ptr;
 
 		next = head->next;
 		debug_rcu_head_unqueue((struct rcu_head *)ptr);
@@ -3342,26 +3342,21 @@ add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
  * be free'd in workqueue context. This allows us to: batch requests together to
  * reduce the number of grace periods during heavy kfree_rcu()/kvfree_rcu() load.
  */
-void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
+void kvfree_call_rcu(struct rcu_head *head, void *ptr)
 {
 	unsigned long flags;
 	struct kfree_rcu_cpu *krcp;
 	bool success;
-	void *ptr;
 
-	if (head) {
-		ptr = (void *) head - (unsigned long) func;
-	} else {
-		/*
-		 * Please note there is a limitation for the head-less
-		 * variant, that is why there is a clear rule for such
-		 * objects: it can be used from might_sleep() context
-		 * only. For other places please embed an rcu_head to
-		 * your data.
-		 */
+	/*
+	 * Please note there is a limitation for the head-less
+	 * variant, that is why there is a clear rule for such
+	 * objects: it can be used from might_sleep() context
+	 * only. For other places please embed an rcu_head to
+	 * your data.
+	 */
+	if (!head)
 		might_sleep();
-		ptr = (unsigned long *) func;
-	}
 
 	// Queue the object but don't yet schedule the batch.
 	if (debug_rcu_head_queue(ptr)) {
@@ -3382,7 +3377,7 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
 			// Inline if kvfree_rcu(one_arg) call.
 			goto unlock_return;
 
-		head->func = func;
+		head->func = ptr;
 		head->next = krcp->head;
 		krcp->head = head;
 		success = true;