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Subject[PATCH 11/15] workqueue: reorganize try_to_grab_pending() and __cancel_timer_work()
Date
* Move timer handling from __cancel_work_timer() to
try_to_grab_pending().

* Make try_to_grab_pending() use -EAGAIN instead of -1 for
busy-looping and drop the ret local variable.

* Add proper function comment to try_to_grab_pending().

This makes the code a bit easier to understand and will ease further
changes. This patch doesn't make any functional change.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
kernel/workqueue.c | 36 +++++++++++++++++++++++++-----------
1 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 358779c..a0eb033 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1004,15 +1004,29 @@ static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq, int color,
complete(&cwq->wq->first_flusher->done);
}

-/*
- * Upon a successful return (>= 0), the caller "owns" WORK_STRUCT_PENDING bit,
- * so this work can't be re-armed in any way.
+/**
+ * try_to_grab_pending - steal work item from worklist
+ * @work: work item to steal
+ *
+ * Try to grab PENDING bit of @work. This function can handle @work in any
+ * stable state - idle, on timer or on worklist. Return values are
+ *
+ * 1 if @work was pending and we successfully stole PENDING
+ * 0 if @work was idle and we claimed PENDING
+ * -EAGAIN if PENDING couldn't be grabbed at the moment, safe to busy-retry
+ *
+ * On >= 0 return, the caller owns @work's PENDING bit.
*/
-static int try_to_grab_pending(struct work_struct *work)
+static int try_to_grab_pending(struct work_struct *work,
+ struct timer_list *timer)
{
struct global_cwq *gcwq;
- int ret = -1;

+ /* try to steal the timer if it exists */
+ if (timer && likely(del_timer(timer)))
+ return 1;
+
+ /* try to claim PENDING the normal way */
if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)))
return 0;

@@ -1022,7 +1036,7 @@ static int try_to_grab_pending(struct work_struct *work)
*/
gcwq = get_work_gcwq(work);
if (!gcwq)
- return ret;
+ return -EAGAIN;

spin_lock_irq(&gcwq->lock);
if (!list_empty(&work->entry)) {
@@ -1038,12 +1052,14 @@ static int try_to_grab_pending(struct work_struct *work)
cwq_dec_nr_in_flight(get_work_cwq(work),
get_work_color(work),
*work_data_bits(work) & WORK_STRUCT_DELAYED);
- ret = 1;
+
+ spin_unlock_irq(&gcwq->lock);
+ return 1;
}
}
spin_unlock_irq(&gcwq->lock);

- return ret;
+ return -EAGAIN;
}

/**
@@ -2823,9 +2839,7 @@ static bool __cancel_work_timer(struct work_struct *work,
int ret;

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

--
1.7.7.3


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