sched/wait: Standardize wait_bit_queue naming

So wait-bit-queue head variables are often named:

	struct wait_bit_queue *q

... which is a bit ambiguous and super confusing, because
they clearly suggest wait-queue head semantics and behavior
(they rhyme with the old wait_queue_t *q naming), while they
are extended wait-queue _entries_, not heads!

They are misnomers in two ways:

 - the 'wait_bit_queue' leaves open the question of whether
   it's an entry or a head

 - the 'q' parameter and local variable naming falsely implies
   that it's a 'queue' - while it's an entry.

This resulted in sometimes confusing cases such as:

	finish_wait(wq, &q->wait);

where the 'q' is not a wait-queue head, but a wait-bit-queue entry.

So improve this all by standardizing wait-bit-queue nomenclature
similar to wait-queue head naming:

	struct wait_bit_queue   => struct wait_bit_queue_entry
	q			=> wbq_entry

Which makes it all a much clearer:

	struct wait_bit_queue_entry *wbq_entry

... and turns the former confusing piece of code into:

	finish_wait(wq_head, &wbq_entry->wq_entry;

which IMHO makes it apparently clear what we are doing,
without having to analyze the context of the code: we are
adding a wait-queue entry to a regular wait-queue head,
which entry is embedded in a wait-bit-queue entry.

I'm not a big fan of acronyms, but repeating wait_bit_queue_entry
in field and local variable names is too long, so Hopefully it's
clear enough that 'wq_' prefixes stand for wait-queues, while
'wbq_' prefixes stand for wait-bit-queues.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/wait.h

@@ -36,7 +36,7 @@ struct wait_bit_key {
 	unsigned long		timeout;
 };
 
-struct wait_bit_queue {
+struct wait_bit_queue_entry {
 	struct wait_bit_key	key;
 	struct wait_queue_entry	wq_entry;
 };
@@ -207,8 +207,8 @@ void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode, int
 void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr);
 void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode, int nr);
 void __wake_up_bit(struct wait_queue_head *, void *, int);
-int __wait_on_bit(struct wait_queue_head *, struct wait_bit_queue *, wait_bit_action_f *, unsigned);
-int __wait_on_bit_lock(struct wait_queue_head *, struct wait_bit_queue *, wait_bit_action_f *, unsigned);
+int __wait_on_bit(struct wait_queue_head *, struct wait_bit_queue_entry *, wait_bit_action_f *, unsigned);
+int __wait_on_bit_lock(struct wait_queue_head *, struct wait_bit_queue_entry *, wait_bit_action_f *, unsigned);
 void wake_up_bit(void *, int);
 void wake_up_atomic_t(atomic_t *);
 int out_of_line_wait_on_bit(void *, int, wait_bit_action_f *, unsigned);
@@ -989,7 +989,7 @@ int wake_bit_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync
 #define DEFINE_WAIT(name) DEFINE_WAIT_FUNC(name, autoremove_wake_function)
 
 #define DEFINE_WAIT_BIT(name, word, bit)				\
-	struct wait_bit_queue name = {					\
+	struct wait_bit_queue_entry name = {				\
 		.key = __WAIT_BIT_KEY_INITIALIZER(word, bit),		\
 		.wq_entry = {						\
 			.private	= current,			\

kernel/sched/wait.c

@@ -394,8 +394,7 @@ EXPORT_SYMBOL(woken_wake_function);
 int wake_bit_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *arg)
 {
 	struct wait_bit_key *key = arg;
-	struct wait_bit_queue *wait_bit
-		= container_of(wq_entry, struct wait_bit_queue, wq_entry);
+	struct wait_bit_queue_entry *wait_bit = container_of(wq_entry, struct wait_bit_queue_entry, wq_entry);
 
 	if (wait_bit->key.flags != key->flags ||
 			wait_bit->key.bit_nr != key->bit_nr ||
@@ -412,17 +411,17 @@ EXPORT_SYMBOL(wake_bit_function);
  * permitted return codes. Nonzero return codes halt waiting and return.
  */
 int __sched
-__wait_on_bit(struct wait_queue_head *wq_head, struct wait_bit_queue *q,
+__wait_on_bit(struct wait_queue_head *wq_head, struct wait_bit_queue_entry *wbq_entry,
 	      wait_bit_action_f *action, unsigned mode)
 {
 	int ret = 0;
 
 	do {
-		prepare_to_wait(wq_head, &q->wq_entry, mode);
-		if (test_bit(q->key.bit_nr, q->key.flags))
-			ret = (*action)(&q->key, mode);
-	} while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
-	finish_wait(wq_head, &q->wq_entry);
+		prepare_to_wait(wq_head, &wbq_entry->wq_entry, mode);
+		if (test_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags))
+			ret = (*action)(&wbq_entry->key, mode);
+	} while (test_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags) && !ret);
+	finish_wait(wq_head, &wbq_entry->wq_entry);
 	return ret;
 }
 EXPORT_SYMBOL(__wait_on_bit);
@@ -450,15 +449,15 @@ int __sched out_of_line_wait_on_bit_timeout(
 EXPORT_SYMBOL_GPL(out_of_line_wait_on_bit_timeout);
 
 int __sched
-__wait_on_bit_lock(struct wait_queue_head *wq_head, struct wait_bit_queue *q,
+__wait_on_bit_lock(struct wait_queue_head *wq_head, struct wait_bit_queue_entry *wbq_entry,
 			wait_bit_action_f *action, unsigned mode)
 {
 	int ret = 0;
 
 	for (;;) {
-		prepare_to_wait_exclusive(wq_head, &q->wq_entry, mode);
-		if (test_bit(q->key.bit_nr, q->key.flags)) {
-			ret = action(&q->key, mode);
+		prepare_to_wait_exclusive(wq_head, &wbq_entry->wq_entry, mode);
+		if (test_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags)) {
+			ret = action(&wbq_entry->key, mode);
 			/*
 			 * See the comment in prepare_to_wait_event().
 			 * finish_wait() does not necessarily takes wwq_head->lock,
@@ -466,11 +465,11 @@ __wait_on_bit_lock(struct wait_queue_head *wq_head, struct wait_bit_queue *q,
 			 * smp_mb__after_atomic() before wake_up_page().
 			 */
 			if (ret)
-				finish_wait(wq_head, &q->wq_entry);
+				finish_wait(wq_head, &wbq_entry->wq_entry);
 		}
-		if (!test_and_set_bit(q->key.bit_nr, q->key.flags)) {
+		if (!test_and_set_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags)) {
 			if (!ret)
-				finish_wait(wq_head, &q->wq_entry);
+				finish_wait(wq_head, &wbq_entry->wq_entry);
 			return 0;
 		} else if (ret) {
 			return ret;
@@ -538,7 +537,7 @@ static int wake_atomic_t_function(struct wait_queue_entry *wq_entry, unsigned mo
 				  void *arg)
 {
 	struct wait_bit_key *key = arg;
-	struct wait_bit_queue *wait_bit = container_of(wq_entry, struct wait_bit_queue, wq_entry);
+	struct wait_bit_queue_entry *wait_bit = container_of(wq_entry, struct wait_bit_queue_entry, wq_entry);
 	atomic_t *val = key->flags;
 
 	if (wait_bit->key.flags != key->flags ||
@@ -554,25 +553,25 @@ static int wake_atomic_t_function(struct wait_queue_entry *wq_entry, unsigned mo
  * return codes halt waiting and return.
  */
 static __sched
-int __wait_on_atomic_t(struct wait_queue_head *wq_head, struct wait_bit_queue *q,
+int __wait_on_atomic_t(struct wait_queue_head *wq_head, struct wait_bit_queue_entry *wbq_entry,
 		       int (*action)(atomic_t *), unsigned mode)
 {
 	atomic_t *val;
 	int ret = 0;
 
 	do {
-		prepare_to_wait(wq_head, &q->wq_entry, mode);
-		val = q->key.flags;
+		prepare_to_wait(wq_head, &wbq_entry->wq_entry, mode);
+		val = wbq_entry->key.flags;
 		if (atomic_read(val) == 0)
 			break;
 		ret = (*action)(val);
 	} while (!ret && atomic_read(val) != 0);
-	finish_wait(wq_head, &q->wq_entry);
+	finish_wait(wq_head, &wbq_entry->wq_entry);
 	return ret;
 }
 
 #define DEFINE_WAIT_ATOMIC_T(name, p)					\
-	struct wait_bit_queue name = {					\
+	struct wait_bit_queue_entry name = {				\
 		.key = __WAIT_ATOMIC_T_KEY_INITIALIZER(p),		\
 		.wq_entry = {						\
 			.private	= current,			\