From dbb92f88648d6206bf22fcb764fb9fe2939d401a Mon Sep 17 00:00:00 2001 From: Andrea Parri Date: Wed, 22 Jan 2020 19:39:52 +0100 Subject: workqueue: Document (some) memory-ordering properties of {queue,schedule}_work() 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 Signed-off-by: Andrea Parri Acked-by: Paul E. McKenney Signed-off-by: Tejun Heo --- include/linux/workqueue.h | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) (limited to 'include/linux/workqueue.h') diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h index 4261d1c6e87b..e48554e6526c 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(), cf. the + * DocBook header of queue_work(). */ static inline bool schedule_work(struct work_struct *work) { -- cgit v1.2.3 From 2333e829952fb437db915bbb17f4d8c43127d438 Mon Sep 17 00:00:00 2001 From: Yu Chen Date: Sun, 23 Feb 2020 15:28:52 +0800 Subject: workqueue: Make workqueue_init*() return void The return values of workqueue_init() and workqueue_early_int() are always 0, and there is no usage of their return value. So just make them return void. Signed-off-by: Yu Chen Signed-off-by: Tejun Heo --- include/linux/workqueue.h | 4 ++-- kernel/workqueue.c | 8 ++------ 2 files changed, 4 insertions(+), 8 deletions(-) (limited to 'include/linux/workqueue.h') diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h index 4261d1c6e87b..c86a7691e13c 100644 --- a/include/linux/workqueue.h +++ b/include/linux/workqueue.h @@ -649,7 +649,7 @@ int workqueue_online_cpu(unsigned int cpu); int workqueue_offline_cpu(unsigned int cpu); #endif -int __init workqueue_init_early(void); -int __init workqueue_init(void); +void __init workqueue_init_early(void); +void __init workqueue_init(void); #endif diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 301db4406bc3..5afa9ad45eba 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -5896,7 +5896,7 @@ static void __init wq_numa_init(void) * items. Actual work item execution starts only after kthreads can be * created and scheduled right before early initcalls. */ -int __init workqueue_init_early(void) +void __init workqueue_init_early(void) { int std_nice[NR_STD_WORKER_POOLS] = { 0, HIGHPRI_NICE_LEVEL }; int hk_flags = HK_FLAG_DOMAIN | HK_FLAG_WQ; @@ -5963,8 +5963,6 @@ int __init workqueue_init_early(void) !system_unbound_wq || !system_freezable_wq || !system_power_efficient_wq || !system_freezable_power_efficient_wq); - - return 0; } /** @@ -5976,7 +5974,7 @@ int __init workqueue_init_early(void) * are no kworkers executing the work items yet. Populate the worker pools * with the initial workers and enable future kworker creations. */ -int __init workqueue_init(void) +void __init workqueue_init(void) { struct workqueue_struct *wq; struct worker_pool *pool; @@ -6023,6 +6021,4 @@ int __init workqueue_init(void) wq_online = true; wq_watchdog_init(); - - return 0; } -- cgit v1.2.3