We are going to use kthread_worker more widely and delayed works
will be pretty useful.
The implementation is inspired by workqueues. It uses a timer to
queue the work after the requested delay. If the delay is zero,
the work is queued immediately.
In compare with workqueues, each work is associated with a single
worker (kthread). Therefore the implementation could be much easier.
In particular, we use the worker->lock to synchronized all the
operations with the work. We do not need any atomic operation
with a flags variable.
We even do not need to maintain any state variable. Instead, we
add a pointer[*] to the timer into the struct kthread_work. Then
we could detect the pending status using a rather simple check,
see the new kthread_worker_pending() function.
Finally, the timer callback knows only about the struct work.
It is better be paranoid and try to get the worker->lock carefully.
The try_lock_thread_work() function will be later useful also when
canceling the work.
[*] I considered also adding the entire struct timer_list into
struct kthread_work. But it would increase the size from
40 to 120 bytes on x86_64 with an often unused stuff.
Another alternative was to add a flags variable. But this
would add an extra code to synchronize it with the state
of the timer.
Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
---
include/linux/kthread.h | 34 ++++++++++++
kernel/kthread.c | 142 +++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 174 insertions(+), 2 deletions(-)
diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index c4a95a3ba500..1a5738dcdf8d 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -63,6 +63,7 @@ extern int tsk_fork_get_node(struct task_struct *tsk);
*/
struct kthread_work;
typedef void (*kthread_work_func_t)(struct kthread_work *work);
+void delayed_kthread_work_timer_fn(unsigned long __data);
struct kthread_worker {
spinlock_t lock;
@@ -75,6 +76,12 @@ struct kthread_work {
struct list_head node;
kthread_work_func_t func;
struct kthread_worker *worker;
+ struct timer_list *timer;
+};
+
+struct delayed_kthread_work {
+ struct kthread_work work;
+ struct timer_list timer;
};
#define KTHREAD_WORKER_INIT(worker) { \
@@ -87,12 +94,24 @@ struct kthread_work {
.func = (fn), \
}
+#define DELAYED_KTHREAD_WORK_INIT(dwork, fn) { \
+ .work = KTHREAD_WORK_INIT((dwork).work, (fn)), \
+ .timer = __TIMER_INITIALIZER(delayed_kthread_work_timer_fn, \
+ 0, (unsigned long)&(dwork), \
+ TIMER_IRQSAFE), \
+ .work.timer = &(dwork).timer, \
+ }
+
#define DEFINE_KTHREAD_WORKER(worker) \
struct kthread_worker worker = KTHREAD_WORKER_INIT(worker)
#define DEFINE_KTHREAD_WORK(work, fn) \
struct kthread_work work = KTHREAD_WORK_INIT(work, fn)
+#define DEFINE_DELAYED_KTHREAD_WORK(dwork, fn) \
+ struct delayed_kthread_work dwork = \
+ DELAYED_KTHREAD_WORK_INIT(dwork, fn)
+
/*
* kthread_worker.lock needs its own lockdep class key when defined on
* stack with lockdep enabled. Use the following macros in such cases.
@@ -122,6 +141,16 @@ extern void __init_kthread_worker(struct kthread_worker *worker,
(work)->func = (fn); \
} while (0)
+#define init_delayed_kthread_work(dwork, fn) \
+ do { \
+ init_kthread_work(&(dwork)->work, (fn)); \
+ __setup_timer(&(dwork)->timer, \
+ delayed_kthread_work_timer_fn, \
+ (unsigned long)(dwork), \
+ TIMER_IRQSAFE); \
+ (dwork)->work.timer = &(dwork)->timer; \
+ } while (0)
+
int kthread_worker_fn(void *worker_ptr);
__printf(1, 2)
@@ -133,6 +162,11 @@ create_kthread_worker_on_cpu(int cpu, const char namefmt[]);
bool queue_kthread_work(struct kthread_worker *worker,
struct kthread_work *work);
+
+bool queue_delayed_kthread_work(struct kthread_worker *worker,
+ struct delayed_kthread_work *dwork,
+ unsigned long delay);
+
void flush_kthread_work(struct kthread_work *work);
void flush_kthread_worker(struct kthread_worker *worker);
diff --git a/kernel/kthread.c b/kernel/kthread.c
index e12576bc0e39..6933d90c0fec 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -563,6 +563,20 @@ void __init_kthread_worker(struct kthread_worker *worker,
}
EXPORT_SYMBOL_GPL(__init_kthread_worker);
+/*
+ * Returns true when there is a pending operation for this work.
+ * In particular, it checks if the work is:
+ * - queued
+ * - a timer is running to queue this delayed work
+ *
+ * This function must be called with locked work.
+ */
+static inline bool kthread_work_pending(const struct kthread_work *work)
+{
+ return !list_empty(&work->node) ||
+ (work->timer && timer_active(work->timer));
+}
+
/**
* kthread_worker_fn - kthread function to process kthread_worker
* @worker_ptr: pointer to initialized kthread_worker
@@ -722,6 +736,15 @@ static void insert_kthread_work(struct kthread_worker *worker,
wake_up_process(worker->task);
}
+/*
+ * Queue @work right into the worker queue.
+ */
+static void __queue_kthread_work(struct kthread_worker *worker,
+ struct kthread_work *work)
+{
+ insert_kthread_work(worker, work, &worker->work_list);
+}
+
/**
* queue_kthread_work - queue a kthread_work
* @worker: target kthread_worker
@@ -747,8 +770,8 @@ bool queue_kthread_work(struct kthread_worker *worker,
unsigned long flags;
spin_lock_irqsave(&worker->lock, flags);
- if (list_empty(&work->node)) {
- insert_kthread_work(worker, work, &worker->work_list);
+ if (!kthread_work_pending(work)) {
+ __queue_kthread_work(worker, work);
ret = true;
}
spin_unlock_irqrestore(&worker->lock, flags);
@@ -756,6 +779,121 @@ bool queue_kthread_work(struct kthread_worker *worker,
}
EXPORT_SYMBOL_GPL(queue_kthread_work);
+static bool try_lock_kthread_work(struct kthread_work *work)
+{
+ struct kthread_worker *worker;
+ int ret = false;
+
+try_again:
+ worker = work->worker;
+
+ if (!worker)
+ goto out;
+
+ spin_lock(&worker->lock);
+ if (worker != work->worker) {
+ spin_unlock(&worker->lock);
+ goto try_again;
+ }
+ ret = true;
+
+out:
+ return ret;
+}
+
+static inline void unlock_kthread_work(struct kthread_work *work)
+{
+ spin_unlock(&work->worker->lock);
+}
+
+/**
+ * delayed_kthread_work_timer_fn - callback that queues the associated delayed
+ * kthread work when the timer expires.
+ * @__data: pointer to the data associated with the timer
+ *
+ * The format of the function is defined by struct timer_list.
+ * It should have been called from irqsafe timer with irq already off.
+ */
+void delayed_kthread_work_timer_fn(unsigned long __data)
+{
+ struct delayed_kthread_work *dwork =
+ (struct delayed_kthread_work *)__data;
+ struct kthread_work *work = &dwork->work;
+
+ if (!try_lock_kthread_work(work))
+ return;
+
+ __queue_kthread_work(work->worker, work);
+ unlock_kthread_work(work);
+}
+EXPORT_SYMBOL(delayed_kthread_work_timer_fn);
+
+void __queue_delayed_kthread_work(struct kthread_worker *worker,
+ struct delayed_kthread_work *dwork,
+ unsigned long delay)
+{
+ struct timer_list *timer = &dwork->timer;
+ struct kthread_work *work = &dwork->work;
+
+ WARN_ON_ONCE(timer->function != delayed_kthread_work_timer_fn ||
+ timer->data != (unsigned long)dwork);
+ WARN_ON_ONCE(timer_pending(timer));
+
+ /*
+ * If @delay is 0, queue @dwork->work immediately. This is for
+ * both optimization and correctness. The earliest @timer can
+ * expire is on the closest next tick and delayed_work users depend
+ * on that there's no such delay when @delay is 0.
+ */
+ if (!delay) {
+ __queue_kthread_work(worker, work);
+ return;
+ }
+
+ /* Be paranoid and try to detect possible races already now. */
+ insert_kthread_work_sanity_check(worker, work);
+
+ work->worker = worker;
+ timer_stats_timer_set_start_info(&dwork->timer);
+ timer->expires = jiffies + delay;
+ add_timer(timer);
+}
+
+/**
+ * queue_delayed_kthread_work - queue the associated kthread work
+ * after a delay.
+ * @worker: target kthread_worker
+ * @work: kthread_work to queue
+ * delay: number of jiffies to wait before queuing
+ *
+ * If the work has not been pending it starts a timer that will queue
+ * the work after the given @delay. If @delay is zero, it queues the
+ * work immediately.
+ *
+ * Return: %false if the @work has already been pending. It means that
+ * either the timer was running or the work was queued. It returns %true
+ * otherwise.
+ */
+bool queue_delayed_kthread_work(struct kthread_worker *worker,
+ struct delayed_kthread_work *dwork,
+ unsigned long delay)
+{
+ struct kthread_work *work = &dwork->work;
+ unsigned long flags;
+ bool ret = false;
+
+ spin_lock_irqsave(&worker->lock, flags);
+
+ if (!kthread_work_pending(work)) {
+ __queue_delayed_kthread_work(worker, dwork, delay);
+ ret = true;
+ }
+
+ spin_unlock_irqrestore(&worker->lock, flags);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(queue_delayed_kthread_work);
+
struct kthread_flush_work {
struct kthread_work work;
struct completion done;
--
1.8.5.6
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