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Subject[PATCH v3 10/22] kthread: Allow to modify delayed kthread work
Date
There are situations when we need to modify the delay of a delayed kthread
work. For example, when the work depends on an event and the initial delay
means a timeout. Then we want to queue the work immediately when the event
happens.

This patch implements mod_delayed_kthread_work() as inspired workqueues.
It tries to cancel the pending work and queue it again with the
given timeout.

A very special case is when the work is being canceled at the same time.
cancel_*kthread_work_sync() operation blocks queuing until the running
work finishes. Therefore we do nothing and let cancel() win. This should
not normally happen as the caller is supposed to synchronize these
operations a reasonable way.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
include/linux/kthread.h | 4 ++++
kernel/kthread.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 54 insertions(+)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index dd2a587a2bd7..f501dfeaa0e3 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -168,6 +168,10 @@ bool queue_delayed_kthread_work(struct kthread_worker *worker,
struct delayed_kthread_work *dwork,
unsigned long delay);

+bool mod_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 d12aa91cc44d..4c3b845c719e 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -1003,6 +1003,56 @@ out:
return ret;
}

+/**
+ * mod_delayed_kthread_work - modify delay of or queue a delayed kthread work
+ * @worker: kthread worker to use
+ * @dwork: delayed kthread work to queue
+ * @delay: number of jiffies to wait before queuing
+ *
+ * If @dwork is idle, equivalent to queue_delayed_kthread work(). Otherwise,
+ * modify @dwork's timer so that it expires after @delay. If @delay is zero,
+ * @work is guaranteed to be queued immediately.
+ *
+ * Return: %false if @dwork was idle and queued. Return %true if @dwork was
+ * pending and its timer was modified.
+ *
+ * A special case is when cancel_work_sync() is running in parallel.
+ * It blocks further queuing. We let the cancel() win and return %false.
+ * The caller is supposed to synchronize these operations a reasonable way.
+ *
+ * This function is safe to call from any context including IRQ handler.
+ * See try_to_grab_pending_kthread_work() for details.
+ */
+bool mod_delayed_kthread_work(struct kthread_worker *worker,
+ struct delayed_kthread_work *dwork,
+ unsigned long delay)
+{
+ struct kthread_work *work = &dwork->work;
+ unsigned long flags;
+ int ret = 0;
+
+try_again:
+ spin_lock_irqsave(&worker->lock, flags);
+ WARN_ON_ONCE(work->worker && work->worker != worker);
+
+ if (work->canceling)
+ goto out;
+
+ ret = try_to_cancel_kthread_work(work, &worker->lock, &flags);
+ if (ret == -EAGAIN)
+ goto try_again;
+
+ if (work->canceling)
+ ret = 0;
+ else
+ __queue_delayed_kthread_work(worker, dwork, delay);
+
+out:
+ spin_unlock_irqrestore(&worker->lock, flags);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(mod_delayed_kthread_work);
+
static bool __cancel_kthread_work_sync(struct kthread_work *work)
{
struct kthread_worker *worker;
--
1.8.5.6


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