Re: [PATCH] cancel_delayed_work: use del_timer() instead of del_timer_sync()

[Oleg Nesterov <oleg@tv-sign.ru>]

On 04/27, Jarek Poplawski wrote:
>
> According to workqueue.h:
> > /*
> >  * 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_workqueue() or cancel_work_sync() to wait on it.
> >  */
> > static inline int cancel_delayed_work(struct delayed_work *work)
> 
> So, we can do something like this:
> 
> cancel_delayed_work(dwork);
> flush_workqueue(wq);
> kfree(some_obj_used_by_dwork_func);
> 
> And this is enough to work with not rearming work.
> 
> But no more after this patch...

Yes, you are right, and so this patch is wrong.

This is even documented in the changelog, with this change cancel_delayed_work()
may return while the queueing is in progress. However, in that case we can not
rely on flush_workqueue/cancel_work_sync.

Thanks a lot!

Oleg.