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Commit 1f1f642e authored Jul 15, 2007 by Oleg Nesterov Committed by Linus Torvalds Jul 16, 2007

make cancel_xxx_work_sync() return a boolean



Change cancel_work_sync() and cancel_delayed_work_sync() to return a boolean
indicating whether the work was actually cancelled.  A zero return value means
that the work was not pending/queued.

Without that kind of change it is not possible to avoid flush_workqueue()
sometimes, see the next patch as an example.

Also, this patch unifies both functions and kills the (unlikely) busy-wait
loop.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Jarek Poplawski <jarkao2@o2.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent f5a421a4

include/linux/workqueue.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -148,7 +148,7 @@ extern int keventd_up(void);
		extern void init_workqueues(void);
		int execute_in_process_context(work_func_t fn, struct execute_work *);

		extern void cancel_work_sync(struct work_struct *work);
		extern int cancel_work_sync(struct work_struct *work);

		/*
		* Kill off a pending schedule_delayed_work(). Note that the work callback
		@@ -166,7 +166,7 @@ static inline int cancel_delayed_work(struct delayed_work *work)
		return ret;
		}

		extern void cancel_delayed_work_sync(struct delayed_work *work);
		extern int cancel_delayed_work_sync(struct delayed_work *work);

		/* Obsolete. use cancel_delayed_work_sync() */
		static inline

kernel/workqueue.c

+27 −14

Original line number	Diff line number	Diff line
		@@ -382,16 +382,16 @@ void fastcall flush_workqueue(struct workqueue_struct *wq)
		EXPORT_SYMBOL_GPL(flush_workqueue);

		/*
		* Upon a successful return, the caller "owns" WORK_STRUCT_PENDING bit,
		* Upon a successful return (>= 0), the caller "owns" WORK_STRUCT_PENDING bit,
		* so this work can't be re-armed in any way.
		*/
		static int try_to_grab_pending(struct work_struct *work)
		{
		struct cpu_workqueue_struct *cwq;
		int ret = 0;
		int ret = -1;

		if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work)))
		return 1;
		return 0;

		/*
		* The queueing is in progress, or it is already queued. Try to
		@@ -457,10 +457,28 @@ static void wait_on_work(struct work_struct *work)
		wait_on_cpu_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
		}

		static int __cancel_work_timer(struct work_struct *work,
		struct timer_list* timer)
		{
		int ret;

		do {
		ret = (timer && likely(del_timer(timer)));
		if (!ret)
		ret = try_to_grab_pending(work);
		wait_on_work(work);
		} while (unlikely(ret < 0));

		work_clear_pending(work);
		return ret;
		}

		/**
		* cancel_work_sync - block until a work_struct's callback has terminated
		* @work: the work which is to be flushed
		*
		* Returns true if @work was pending.
		*
		* cancel_work_sync() will cancel the work if it is queued. If the work's
		* callback appears to be running, cancel_work_sync() will block until it
		* has completed.
		@@ -476,12 +494,9 @@ static void wait_on_work(struct work_struct *work)
		* The caller must ensure that workqueue_struct on which this work was last
		* queued can't be destroyed before this function returns.
		*/
		void cancel_work_sync(struct work_struct *work)
		int cancel_work_sync(struct work_struct *work)
		{
		while (!try_to_grab_pending(work))
		cpu_relax();
		wait_on_work(work);
		work_clear_pending(work);
		return __cancel_work_timer(work, NULL);
		}
		EXPORT_SYMBOL_GPL(cancel_work_sync);

		@@ -489,16 +504,14 @@ EXPORT_SYMBOL_GPL(cancel_work_sync);
		* cancel_delayed_work_sync - reliably kill off a delayed work.
		* @dwork: the delayed work struct
		*
		* Returns true if @dwork was pending.
		*
		* It is possible to use this function if @dwork rearms itself via queue_work()
		* or queue_delayed_work(). See also the comment for cancel_work_sync().
		*/
		void cancel_delayed_work_sync(struct delayed_work *dwork)
		int cancel_delayed_work_sync(struct delayed_work *dwork)
		{
		while (!del_timer(&dwork->timer) &&
		!try_to_grab_pending(&dwork->work))
		cpu_relax();
		wait_on_work(&dwork->work);
		work_clear_pending(&dwork->work);
		return __cancel_work_timer(&dwork->work, &dwork->timer);
		}
		EXPORT_SYMBOL(cancel_delayed_work_sync);