[patch V4 43/68] locking/ww_mutex: Abstract waiter iteration

[Thomas Gleixner <tglx@linutronix.de>]

From: Peter Zijlstra <peterz@infradead.org>

Split out the waiter iteration functions so they can be substituted for a
rtmutex based ww_mutex later.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/locking/ww_mutex.h |   57 ++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 53 insertions(+), 4 deletions(-)
---
--- a/kernel/locking/ww_mutex.h
+++ b/kernel/locking/ww_mutex.h
@@ -1,5 +1,49 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+static inline struct mutex_waiter *
+__ww_waiter_first(struct mutex *lock)
+{
+	struct mutex_waiter *w;
+
+	w = list_first_entry(&lock->wait_list, struct mutex_waiter, list);
+	if (list_entry_is_head(w, &lock->wait_list, list))
+		return NULL;
+
+	return w;
+}
+
+static inline struct mutex_waiter *
+__ww_waiter_next(struct mutex *lock, struct mutex_waiter *w)
+{
+	w = list_next_entry(w, list);
+	if (list_entry_is_head(w, &lock->wait_list, list))
+		return NULL;
+
+	return w;
+}
+
+static inline struct mutex_waiter *
+__ww_waiter_prev(struct mutex *lock, struct mutex_waiter *w)
+{
+	w = list_prev_entry(w, list);
+	if (list_entry_is_head(w, &lock->wait_list, list))
+		return NULL;
+
+	return w;
+}
+
+static inline struct mutex_waiter *
+__ww_waiter_last(struct mutex *lock)
+{
+	struct mutex_waiter *w;
+
+	w = list_last_entry(&lock->wait_list, struct mutex_waiter, list);
+	if (list_entry_is_head(w, &lock->wait_list, list))
+		return NULL;
+
+	return w;
+}
+
 /*
  * Wait-Die:
  *   The newer transactions are killed when:
@@ -161,7 +205,9 @@ static void
 
 	lockdep_assert_held(&lock->wait_lock);
 
-	list_for_each_entry(cur, &lock->wait_list, list) {
+	for (cur = __ww_waiter_first(lock); cur;
+	     cur = __ww_waiter_next(lock, cur)) {
+
 		if (!cur->ww_ctx)
 			continue;
 
@@ -263,8 +309,9 @@ static inline int
 	 * If there is a waiter in front of us that has a context, then its
 	 * stamp is earlier than ours and we must kill ourself.
 	 */
-	cur = waiter;
-	list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) {
+	for (cur = __ww_waiter_prev(lock, waiter); cur;
+	     cur = __ww_waiter_prev(lock, cur)) {
+
 		if (!cur->ww_ctx)
 			continue;
 
@@ -309,7 +356,9 @@ static inline int
 	 * may wound the lock holder.
 	 */
 	pos = &lock->wait_list;
-	list_for_each_entry_reverse(cur, &lock->wait_list, list) {
+	for (cur = __ww_waiter_last(lock); cur;
+	     cur = __ww_waiter_prev(lock, cur)) {
+
 		if (!cur->ww_ctx)
 			continue;