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SubjectRe: [PATCH] workqueue: doc: Call out the non-reentrance conditions
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

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