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Subject[PATCH 2/3] 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>

--- OLD/include/linux/workqueue.h~2_retval 2007-06-02 14:26:54.000000000 +0400
+++ OLD/include/linux/workqueue.h 2007-07-01 16:02:32.000000000 +0400
@@ -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(st
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
--- OLD/kernel/workqueue.c~2_retval 2007-07-01 15:02:12.000000000 +0400
+++ OLD/kernel/workqueue.c 2007-07-01 16:56:22.000000000 +0400
@@ -382,16 +382,16 @@ void fastcall flush_workqueue(struct wor
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_str
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_str
* 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);

-
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