[PATCH 02/16] cancel_delayed_work: use del_timer() instead ofdel_timer_sync() [try #3]

From: David Howells
Date: Wed Apr 25 2007 - 06:51:46 EST

del_timer_sync() buys nothing for cancel_delayed_work(), but it is less
efficient since it locks the timer unconditionally, and may wait for the
completion of the delayed_work_timer_fn().

cancel_delayed_work() == 0 means:

before this patch:
work->func may still be running or queued

after this patch:
work->func may still be running or queued, or
delayed_work_timer_fn->__queue_work() in progress.

The latter doesn't differ from the caller's POV,
delayed_work_timer_fn() is called with _PENDING
bit set.

cancel_delayed_work() == 1 with this patch adds a new possibility:

delayed_work->work was cancelled, but delayed_work_timer_fn
is still running (this is only possible for the re-arming
works on single-threaded workqueue).

In this case the timer was re-started by work->func(), nobody
else can do this. This in turn means that delayed_work_timer_fn
has already passed __queue_work() (and wont't touch delayed_work)
because nobody else can queue delayed_work->work.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-Off-By: David Howells <dhowells@xxxxxxxxxx>

include/linux/workqueue.h | 7 ++++---
1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 2a7b38d..b8abfc7 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -191,14 +191,15 @@ int execute_in_process_context(work_func_t fn, struct execute_work *);

* Kill off a pending schedule_delayed_work(). Note that the work callback
- * function may still be running on return from cancel_delayed_work(). Run
- * flush_scheduled_work() to wait on it.
+ * function may still be running on return from cancel_delayed_work(), unless
+ * it returns 1 and the work doesn't re-arm itself. Run flush_workqueue() or
+ * cancel_work_sync() to wait on it.
static inline int cancel_delayed_work(struct delayed_work *work)
int ret;

- ret = del_timer_sync(&work->timer);
+ ret = del_timer(&work->timer);
if (ret)
return ret;

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