wait: kill is_sync_wait() (a25d644f) · Commits · 戴 / test

is_sync_wait() is used to distinguish between sync and async waits. Basically sync waits are the ones initialized with init_waitqueue_entry() and async ones with init_waitqueue_func_entry(). The sync/async distinction is used only in prepare_to_wait[_exclusive]() and its only function is to skip setting the current task state if the wait is async. This has a few problems. * No one uses it. None of func_entry users use prepare_to_wait() functions, so the code path never gets executed. * The distinction is bogus. Maybe back when func_entry is used only by aio but it's now also used by epoll and in future possibly by 9p and poll/select. * Taking @state as argument and ignoring it silenly depending on how @wait is initialized is just a bad error-prone API. * It prevents func_entry waits from using wait->private for no good reason. This patch kills is_sync_wait() and the associated code paths from prepare_to_wait[_exclusive](). As there was no user of these code paths, this patch doesn't cause any behavior difference. Signed-off-by:

Tejun Heo <tj@kernel.org> Acked-by:

Ingo Molnar <mingo@elte.hu> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

include/linux/wait.h

+0 −9

Original line number	Diff line number	Diff line
		@@ -108,15 +108,6 @@ static inline int waitqueue_active(wait_queue_head_t *q)
		return !list_empty(&q->task_list);
		}

		/*
		* Used to distinguish between sync and async io wait context:
		* sync i/o typically specifies a NULL wait queue entry or a wait
		* queue entry bound to a task (current task) to wake up.
		* aio specifies a wait queue entry with an async notification
		* callback routine, not associated with any task.
		*/
		#define is_sync_wait(wait) (!(wait) \|\| ((wait)->private))

		extern void add_wait_queue(wait_queue_head_t q, wait_queue_t wait);
		extern void add_wait_queue_exclusive(wait_queue_head_t q, wait_queue_t wait);
		extern void remove_wait_queue(wait_queue_head_t q, wait_queue_t wait);

kernel/wait.c

+2 −12

Original line number	Diff line number	Diff line
		@@ -72,11 +72,6 @@ prepare_to_wait(wait_queue_head_t q, wait_queue_t wait, int state)
		spin_lock_irqsave(&q->lock, flags);
		if (list_empty(&wait->task_list))
		__add_wait_queue(q, wait);
		/*
		* don't alter the task state if this is just going to
		* queue an async wait queue callback
		*/
		if (is_sync_wait(wait))
		set_current_state(state);
		spin_unlock_irqrestore(&q->lock, flags);
		}
		@@ -91,11 +86,6 @@ prepare_to_wait_exclusive(wait_queue_head_t q, wait_queue_t wait, int state)
		spin_lock_irqsave(&q->lock, flags);
		if (list_empty(&wait->task_list))
		__add_wait_queue_tail(q, wait);
		/*
		* don't alter the task state if this is just going to
		* queue an async wait queue callback
		*/
		if (is_sync_wait(wait))
		set_current_state(state);
		spin_unlock_irqrestore(&q->lock, flags);
		}

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