1 files changed, 75 insertions, 6 deletions

diff --git a/kernel/slow-work.c b/kernel/slow-work.c
index fccf421eb5c1..671cc434532a 100644
--- a/kernel/slow-work.c
+++ b/kernel/slow-work.c
@@ -236,12 +236,17 @@ static bool slow_work_execute(int id)
         if (!test_and_clear_bit(SLOW_WORK_PENDING, &work->flags))
                 BUG();
 
-        work->ops->execute(work);
+        /* don't execute if the work is in the process of being cancelled */
+        if (!test_bit(SLOW_WORK_CANCELLING, &work->flags))
+                work->ops->execute(work);
 
         if (very_slow)
                 atomic_dec(&vslow_work_executing_count);
         clear_bit_unlock(SLOW_WORK_EXECUTING, &work->flags);
 
+        /* wake up anyone waiting for this work to be complete */
+        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
@@ -314,11 +319,16 @@ 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 -ECANCELED if cancelled work is
+ * attempted queued)
  */
 int slow_work_enqueue(struct slow_work *work)
 {
         unsigned long flags;
+        int ret;
+
+        if (test_bit(SLOW_WORK_CANCELLING, &work->flags))
+                return -ECANCELED;
 
         BUG_ON(slow_work_user_count <= 0);
         BUG_ON(!work);
@@ -335,6 +345,9 @@ int slow_work_enqueue(struct slow_work *work)
         if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) {
                 spin_lock_irqsave(&slow_work_queue_lock, flags);
 
+                if (unlikely(test_bit(SLOW_WORK_CANCELLING, &work->flags)))
+                        goto cancelled;
+
                 /* we promise that we will not attempt to execute the work
                  * function in more than one thread simultaneously
                  *
@@ -352,8 +365,9 @@ int slow_work_enqueue(struct slow_work *work)
                 if (test_bit(SLOW_WORK_EXECUTING, &work->flags)) {
                         set_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags);
                 } else {
-                        if (slow_work_get_ref(work) < 0)
-                                goto cant_get_ref;
+                        ret = slow_work_get_ref(work);
+                        if (ret < 0)
+                                goto failed;
                         if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags))
                                 list_add_tail(&work->link, &vslow_work_queue);
                         else
@@ -365,12 +379,67 @@ int slow_work_enqueue(struct slow_work *work)
         }
         return 0;
 
-cant_get_ref:
+cancelled:
+        ret = -ECANCELED;
+failed:
         spin_unlock_irqrestore(&slow_work_queue_lock, flags);
-        return -EAGAIN;
+        return ret;
 }
 EXPORT_SYMBOL(slow_work_enqueue);
 
+static int slow_work_wait(void *word)
+{
+        schedule();
+        return 0;
+}
+
+/**
+ * slow_work_cancel - Cancel a slow work item
+ * @work: The work item to cancel
+ *
+ * This function will cancel a previously enqueued work item. If we cannot
+ * cancel the work item, it is guarenteed to have run when this function
+ * returns.
+ */
+void slow_work_cancel(struct slow_work *work)
+{
+        bool wait = true, put = false;
+
+        set_bit(SLOW_WORK_CANCELLING, &work->flags);
+
+        spin_lock_irq(&slow_work_queue_lock);
+
+        if (test_bit(SLOW_WORK_PENDING, &work->flags) &&
+            !list_empty(&work->link)) {
+                /* the link in the pending queue holds a reference on the item
+                 * that we will need to release */
+                list_del_init(&work->link);
+                wait = false;
+                put = true;
+                clear_bit(SLOW_WORK_PENDING, &work->flags);
+
+        } else if (test_and_clear_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags)) {
+                /* the executor is holding our only reference on the item, so
+                 * we merely need to wait for it to finish executing */
+                clear_bit(SLOW_WORK_PENDING, &work->flags);
+        }
+
+        spin_unlock_irq(&slow_work_queue_lock);
+
+        /* the EXECUTING flag is set by the executor whilst the spinlock is set
+         * and before the item is dequeued - so assuming the above doesn't
+         * actually dequeue it, simply waiting for the EXECUTING flag to be
+         * released here should be sufficient */
+        if (wait)
+                wait_on_bit(&work->flags, SLOW_WORK_EXECUTING, slow_work_wait,
+                            TASK_UNINTERRUPTIBLE);
+
+        clear_bit(SLOW_WORK_CANCELLING, &work->flags);
+        if (put)
+                slow_work_put_ref(work);
+}
+EXPORT_SYMBOL(slow_work_cancel);
+
 /*
  * Schedule a cull of the thread pool at some time in the near future
  */