linux-kernel - [PATCH V2 4/4] sched/wait: introduce init_wait

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Date:   Tue, 6 Sep 2016 16:00:55 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Al Viro <viro@...IV.linux.org.uk>,
        Bart Van Assche <bvanassche@....org>,
        Johannes Weiner <hannes@...xchg.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Neil Brown <neilb@...e.de>, linux-kernel@...r.kernel.org
Subject: [PATCH V2 4/4] sched/wait: introduce init_wait_entry()

The partial initialization of wait_queue_t in prepare_to_wait_event() looks
ugly. This was done to shrink .text, but we can simply add the new helper
which does the full initialization and shrink the compiled code a bit more.

And. This way prepare_to_wait_event() can have more users. In particular we
are ready to remove the signal_pending_state() checks from wait_bit_action_f
helpers and change __wait_on_bit_lock() to use prepare_to_wait_event().

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 include/linux/wait.h |  9 +++------
 kernel/sched/wait.c  | 12 +++++++++---
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/include/linux/wait.h b/include/linux/wait.h
index 52953a5..1b8a930 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -248,6 +248,8 @@ wait_queue_head_t *bit_waitqueue(void *, int);
 	(!__builtin_constant_p(state) ||				\
 		state == TASK_INTERRUPTIBLE || state == TASK_KILLABLE)	\
 
+extern void init_wait_entry(wait_queue_t *__wait, int flags);
+
 /*
  * The below macro ___wait_event() has an explicit shadow of the __ret
  * variable when used from the wait_event_*() macros.
@@ -266,12 +268,7 @@ wait_queue_head_t *bit_waitqueue(void *, int);
 	wait_queue_t __wait;						\
 	long __ret = ret;	/* explicit shadow */			\
 									\
-	INIT_LIST_HEAD(&__wait.task_list);				\
-	if (exclusive)							\
-		__wait.flags = WQ_FLAG_EXCLUSIVE;			\
-	else								\
-		__wait.flags = 0;					\
-									\
+	init_wait_entry(&__wait, exclusive ? WQ_FLAG_EXCLUSIVE : 0);	\
 	for (;;) {							\
 		long __int = prepare_to_wait_event(&wq, &__wait, state);\
 									\
diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index 47c4d62..61dcee1 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -196,14 +196,20 @@ prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
 }
 EXPORT_SYMBOL(prepare_to_wait_exclusive);
 
+void init_wait_entry(wait_queue_t *wait, int flags)
+{
+	wait->flags = flags;
+	wait->private = current;
+	wait->func = autoremove_wake_function;
+	INIT_LIST_HEAD(&wait->task_list);
+}
+EXPORT_SYMBOL(init_wait_entry);
+
 long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state)
 {
 	unsigned long flags;
 	long ret = 0;
 
-	wait->private = current;
-	wait->func = autoremove_wake_function;
-
 	spin_lock_irqsave(&q->lock, flags);
 	if (unlikely(signal_pending_state(state, current))) {
 		/*
-- 
2.5.0