On Thursday, December 17, 2015, Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
On Thu, Dec 17 2015 at 10:50am -0500,
Tejun Heo <tj@xxxxxxxxxx> wrote:
> Hello, Nikolay.
>
> On Thu, Dec 17, 2015 at 05:43:12PM +0200, Nikolay Borisov wrote:
> > Right, but my initial understanding was that when canceling the delayed
> > work and then issuing flush_workqueue would act the same way as if
> > cancel_delayed_work_sync is called wrt to this particular delayed item, no?
>
> Not necessarily. cancel_delayed_work() cancels whatever is currently
> pending. flush_workqueue() flushes whatever is pending and in flight
> at the time of invocation. Imagine the following scenario.
>
> 1. Work item is running but hasn't requeued itself yet.
>
> 2. cancel_delayed_work_sync() doesn't do anything as it's not pending.
Did you mean cancel_delayed_work()?
> 3. flush_workqueue() starts and waits for the running instance.
>
> 4. The running instance requeues itself but this isn't included in the
> scope of the above flush_workqueue().
>
> 5. flush_workqueue() returns when the work item is finished (but it's
> still queued).
Hmm, the comment above cancel_delayed_work() is pretty misleading then:
* Note:
* The work callback function may still be running on return, unless
* it returns %true and the work doesn't re-arm itself. Explicitly flush or
* use cancel_delayed_work_sync() to wait on it.
Given dm-thin.c:pool_postsuspend() does:
cancel_delayed_work(&pool->waker);
cancel_delayed_work(&pool->no_space_timeout);
flush_workqueue(pool->wq);
I wouldn't have thought cancel_delayed_work_sync() was needed.
Ping as Tejun might have missed this email. I'm also interested in knowing the logic behind the comment.
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