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SubjectRe: [PATCH] workqueue: Document (some) memory-ordering properties of {queue,schedule}_work()
On Sun, Jan 19, 2020 at 06:02:35PM -0800, Paul E. McKenney wrote:
> On Sat, Jan 18, 2020 at 10:58:20PM +0100, Andrea Parri wrote:
> > It's desirable to be able to rely on the following property: All stores
> > preceding (in program order) a call to a successful queue_work() will be
> > visible from the CPU which will execute the queued work by the time such
> > work executes, e.g.,
> >
> > { x is initially 0 }
> >
> > CPU0 CPU1
> >
> > WRITE_ONCE(x, 1); [ "work" is being executed ]
> > r0 = queue_work(wq, work); r1 = READ_ONCE(x);
> >
> > Forbids: r0 == true && r1 == 0
> >
> > The current implementation of queue_work() provides such memory-ordering
> > property:
> >
> > - In __queue_work(), the ->lock spinlock is acquired.
> >
> > - On the other side, in worker_thread(), this same ->lock is held
> > when dequeueing work.
> >
> > So the locking ordering makes things work out.
> >
> > Add this property to the DocBook headers of {queue,schedule}_work().
> >
> > Suggested-by: Paul E. McKenney <paulmck@kernel.org>
> > Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
>
> Acked-by: Paul E. McKenney <paulmck@kernel.org>

Thanks!

>
> An alternative to Randy's suggestion of dropping the comma following
> the "cf." is to just drop that whole phrase. I will let you and Randy
> work that one out, though. ;-)

Either way works for me.

I'd give Tejun and Lai some more time to review this and send a non-RFC with
your Ack and this nit fixed later this week (unless I hear some objections).

Thanks,
Andrea

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