[PATCH 2/3] slow-work: add support for cancellation of slow work

[Jens Axboe]

This adds support for cancellation of queued slow work and delayed
slow work. If the work is already queued, it will not be executed.
If work is attempted queued while the cancellation is running,
it will fail.

Signed-off-by: Jens Axboe <jens.axboe@xxxxxxxxxx>
---
 include/linux/slow-work.h |    3 +++
 kernel/slow-work.c        |   42 ++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/include/linux/slow-work.h b/include/linux/slow-work.h
index 12827a8..f2fd4e1 100644
--- a/include/linux/slow-work.h
+++ b/include/linux/slow-work.h
@@ -47,6 +47,7 @@ struct slow_work {
 #define SLOW_WORK_EXECUTING	1	/* item currently executing */
 #define SLOW_WORK_ENQ_DEFERRED	2	/* item enqueue deferred */
 #define SLOW_WORK_VERY_SLOW	3	/* item is very slow */
+#define SLOW_WORK_CANCEL	4	/* item is cancelled, don't enqueue */
 	const struct slow_work_ops *ops; /* operations table for this item */
 	struct list_head	link;	/* link in queue */
 };
@@ -96,11 +97,13 @@ static inline void vslow_work_init(struct slow_work *work,
 }
 
 extern int slow_work_enqueue(struct slow_work *work);
+extern void cancel_slow_work(struct slow_work *work);
 extern int slow_work_register_user(void);
 extern void slow_work_unregister_user(void);
 
 extern int delayed_slow_work_enqueue(struct delayed_slow_work *dwork,
 					unsigned long delay);
+extern void cancel_delayed_slow_work(struct delayed_slow_work *dwork);
 
 #ifdef CONFIG_SYSCTL
 extern ctl_table slow_work_sysctls[];
diff --git a/kernel/slow-work.c b/kernel/slow-work.c
index 1eeda59..9b62bdc 100644
--- a/kernel/slow-work.c
+++ b/kernel/slow-work.c
@@ -194,12 +194,21 @@ static bool slow_work_execute(void)
 	if (!test_and_clear_bit(SLOW_WORK_PENDING, &work->flags))
 		BUG();
 
-	work->ops->execute(work);
+	/*
+	 * Don't execute if the work was cancelled after being added
+	 */
+	if (!test_bit(SLOW_WORK_CANCEL, &work->flags))
+		work->ops->execute(work);
 
 	if (very_slow)
 		atomic_dec(&vslow_work_executing_count);
 	clear_bit_unlock(SLOW_WORK_EXECUTING, &work->flags);
 
+	/*
+	 * Wake anyone waiting for this work to be done
+	 */
+	wake_up_bit(&work->flags, SLOW_WORK_EXECUTING);
+
 	/* if someone tried to enqueue the item whilst we were executing it,
 	 * then it'll be left unenqueued to avoid multiple threads trying to
 	 * execute it simultaneously
@@ -260,12 +269,16 @@ auto_requeue:
  * allowed to pick items to execute.  This ensures that very slow items won't
  * overly block ones that are just ordinarily slow.
  *
- * Returns 0 if successful, -EAGAIN if not.
+ * Returns 0 if successful, -EAGAIN if not (or -EBUSY if cancelled work is
+ * attempted queued)
  */
 int slow_work_enqueue(struct slow_work *work)
 {
 	unsigned long flags;
 
+	if (test_bit(SLOW_WORK_CANCEL, &work->flags))
+		return -EINVAL;
+
 	BUG_ON(slow_work_user_count <= 0);
 	BUG_ON(!work);
 	BUG_ON(!work->ops);
@@ -347,6 +360,9 @@ int delayed_slow_work_enqueue(struct delayed_slow_work *dwork,
 	struct slow_work *work = &dwork->work;
 	unsigned long flags;
 
+	if (test_bit(SLOW_WORK_CANCEL, &work->flags))
+		return -EINVAL;
+
 	BUG_ON(slow_work_user_count <= 0);
 	BUG_ON(!work);
 	BUG_ON(!work->ops);
@@ -377,6 +393,28 @@ cant_get_ref:
 }
 EXPORT_SYMBOL(delayed_slow_work_enqueue);
 
+static int slow_work_wait(void *word)
+{
+	schedule();
+	return 0;
+}
+
+void cancel_slow_work(struct slow_work *work)
+{
+	set_bit(SLOW_WORK_CANCEL, &work->flags);
+	wait_on_bit(&work->flags, SLOW_WORK_EXECUTING, slow_work_wait,
+				TASK_UNINTERRUPTIBLE);
+	clear_bit(SLOW_WORK_CANCEL, &work->flags);
+}
+EXPORT_SYMBOL(cancel_slow_work);
+
+void cancel_delayed_slow_work(struct delayed_slow_work *dwork)
+{
+	del_timer(&dwork->timer);
+	cancel_slow_work(&dwork->work);
+}
+EXPORT_SYMBOL(cancel_delayed_slow_work);
+
 /*
  * Schedule a cull of the thread pool at some time in the near future
  */
-- 
1.6.4.1.207.g68ea

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