On Tue, Oct 19, 2021 at 07:47:56AM -1000, Tejun Heo wrote: > On Mon, Oct 18, 2021 at 09:31:17AM +0800, Boqun Feng wrote: > > +Workqueue guarantees that a work item cannot be re-entrant if the following > > +conditions hold after a work item gets queued: > > + > > + 1. The work function hasn't been changed. > > + 2. No one queues the work item to another workqueue. > > + 3. The work item hasn't been reinitiated. > > Maybe phrasing it so that the above are the conditions defining a work item > to be the same instance would be clearer? > Hmm.. that would mean queue_work_on() may change the work item to another instance? For example: struct work_struct w; INIT_WORK_ONSTACK(w, some_f); queue_work_on(&w, system_wq, 1); // queue a work and create // an instance queue_work_on(&w, system_long_wq, 2); // queue the same work // item but it means // changing it to another // instance. Looks a little counter-intuitive to me, but let me try (combined with Matthew's suggestion) <in Guidelines section> * A work item instance will not be processed by multiple workers at the same time, i.e. it's non-reentrant, so requeuing the same instance of a work item is safe and not racy. Operations considered as changing the work item to a different instance are: 1) change the work function, 2) queue the work item to a different workqueue, or 3) reinitiate the work item. The non-reentrance guarantee doesn't hold for different work item instances. Regards, Boqun > Thanks. > > -- > tejun
