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:
quoted
+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