workqueue: Document (some) memory-ordering properties of {queue,schedule}_work() (dbb92f88) · Commits · 戴 / test

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> Signed-off-by:

Tejun Heo <tj@kernel.org>

include/linux/workqueue.h

+16 −0

Original line number	Diff line number	Diff line
		@@ -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(), cf. the
		* DocBook header of queue_work().
		*/
		static inline bool schedule_work(struct work_struct *work)
		{

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