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sched/wait: Standardize wait_bit_queue naming

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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
parent 2141713616
commit 76c85ddc46
2 changed files with 24 additions and 25 deletions
Download Patch File Download Diff File Expand all files Collapse all files

8
include/linux/wait.h
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@@ -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, \