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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>
This commit is contained in:
Ingo Molnar 2017-03-05 11:35:27 +01:00
Родитель 2141713616
Коммит 76c85ddc46
2 изменённых файлов: 24 добавлений и 25 удалений
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8
include/linux/wait.h
Просмотреть файл

@ -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, \

41
kernel/sched/wait.c
Просмотреть файл

@ -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, \