Messages in this thread | | | Subject | Re: [PATCH] workqueue: Document (some) memory-ordering properties of {queue,schedule}_work() | From | Randy Dunlap <> | Date | Sat, 18 Jan 2020 19:07:06 -0800 |
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Hi,
On 1/18/20 1:58 PM, 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> > --- > include/linux/workqueue.h | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h > index 4261d1c6e87b1..4fef6c38b0536 100644 > --- a/include/linux/workqueue.h > +++ b/include/linux/workqueue.h > @@ -487,6 +487,19 @@ extern void wq_worker_comm(char *buf, size_t size, struct task_struct *task); > * > * We queue the work to the CPU on which it was submitted, but if the CPU dies > * it can be processed by another CPU. > + * > + * Memory-ordering properties: If it returns %true, guarantees that all stores > + * preceding the call to queue_work() in the program order will be visible from > + * the CPU which will execute @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 > */ > static inline bool queue_work(struct workqueue_struct *wq, > struct work_struct *work) > @@ -546,6 +559,9 @@ static inline bool schedule_work_on(int cpu, struct work_struct *work) > * This puts a job in the kernel-global workqueue if it was not already > * queued and leaves it in the same position on the kernel-global > * workqueue otherwise. > + * > + * Shares the same memory-ordering properties of queue_work(), c.f., the
nit: cf. the
> + * DocBook header of queue_work(). > */ > static inline bool schedule_work(struct work_struct *work) > { >
-- ~Randy
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