Hi,
On Fri 2016-06-24 11:54:47, Tejun Heo wrote:
> On Fri, Jun 24, 2016 at 09:05:15AM +0200, Peter Zijlstra wrote:
> > > Given how rare that is
> >
> > Could you then not remove/rework these few cases for workqueue as well
> > and make that 'better' too?
>
> Usage of draining is rare for workqueue but that still means several
> legitimate users. With draining there, it's logical to use it during
> shutdown. I don't think it makes sense to change it on workqueue
> side.
>
> > > and the extra
> > > complexity of identifying self-requeueing cases, let's forget about
> > > draining and on destruction clear the worker pointer to block further
> > > queueing and then flush whatever is in flight.
> >
> > You're talking about regular workqueues here?
>
> No, kthread worker. It's unlikely that kthread worker is gonna need
> chained draining especially given that most of its usages are gonna be
> conversions from raw kthread usages. We won't lose much if anything
> by just ignoring draining and making the code simpler.
OK, so you suggest to do the following:
1. Add a flag into struct kthread_worker that will prevent
from further queuing.
2. kthread_create_worker()/kthread_destroy_worker() will
not longer dynamically allocate struct kthread_worker.
They will just start/stop the kthread.
The result will be:
a. User will not need the strict synchronization between
the queue and create/destroy operations.
b. We could get rid of drain_kthread_worker() because
flush_kthread_worker() will be enough.
IMHO, the 1st change does not make sense without the 2nd one.
Otherwise, users could do an out-of-memory access when testing
the freed kthread_worker flag.
Do I get this correctly please?
Best Regards,
Petr
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