1 files changed, 451 insertions, 43 deletions

diff --git a/kernel/slow-work.c b/kernel/slow-work.c
index 0d31135efbf..da94f3c101a 100644
--- a/kernel/slow-work.c
+++ b/kernel/slow-work.c
@@ -16,11 +16,8 @@
 #include <linux/kthread.h>
 #include <linux/freezer.h>
 #include <linux/wait.h>
-
-#define SLOW_WORK_CULL_TIMEOUT (5 * HZ)	/* cull threads 5s after running out of
-					 * things to do */
-#define SLOW_WORK_OOM_TIMEOUT (5 * HZ)	/* can't start new threads for 5s after
-					 * OOM */
+#include <linux/proc_fs.h>
+#include "slow-work.h"
 
 static void slow_work_cull_timeout(unsigned long);
 static void slow_work_oom_timeout(unsigned long);
@@ -46,7 +43,7 @@ static unsigned vslow_work_proportion = 50; /* % of threads that may process
 
 #ifdef CONFIG_SYSCTL
 static const int slow_work_min_min_threads = 2;
-static int slow_work_max_max_threads = 255;
+static int slow_work_max_max_threads = SLOW_WORK_THREAD_LIMIT;
 static const int slow_work_min_vslow = 1;
 static const int slow_work_max_vslow = 99;
 
@@ -98,6 +95,32 @@ static DEFINE_TIMER(slow_work_oom_timer, slow_work_oom_timeout, 0, 0);
 static struct slow_work slow_work_new_thread; /* new thread starter */
 
 /*
+ * slow work ID allocation (use slow_work_queue_lock)
+ */
+static DECLARE_BITMAP(slow_work_ids, SLOW_WORK_THREAD_LIMIT);
+
+/*
+ * Unregistration tracking to prevent put_ref() from disappearing during module
+ * unload
+ */
+#ifdef CONFIG_MODULES
+static struct module *slow_work_thread_processing[SLOW_WORK_THREAD_LIMIT];
+static struct module *slow_work_unreg_module;
+static struct slow_work *slow_work_unreg_work_item;
+static DECLARE_WAIT_QUEUE_HEAD(slow_work_unreg_wq);
+static DEFINE_MUTEX(slow_work_unreg_sync_lock);
+#endif
+
+/*
+ * Data for tracking currently executing items for indication through /proc
+ */
+#ifdef CONFIG_SLOW_WORK_PROC
+struct slow_work *slow_work_execs[SLOW_WORK_THREAD_LIMIT];
+pid_t slow_work_pids[SLOW_WORK_THREAD_LIMIT];
+DEFINE_RWLOCK(slow_work_execs_lock);
+#endif
+
+/*
  * The queues of work items and the lock governing access to them.  These are
  * shared between all the CPUs.  It doesn't make sense to have per-CPU queues
  * as the number of threads bears no relation to the number of CPUs.
@@ -105,9 +128,18 @@ static struct slow_work slow_work_new_thread; /* new thread starter */
  * There are two queues of work items: one for slow work items, and one for
  * very slow work items.
  */
-static LIST_HEAD(slow_work_queue);
-static LIST_HEAD(vslow_work_queue);
-static DEFINE_SPINLOCK(slow_work_queue_lock);
+LIST_HEAD(slow_work_queue);
+LIST_HEAD(vslow_work_queue);
+DEFINE_SPINLOCK(slow_work_queue_lock);
+
+/*
+ * The following are two wait queues that get pinged when a work item is placed
+ * on an empty queue.  These allow work items that are hogging a thread by
+ * sleeping in a way that could be deferred to yield their thread and enqueue
+ * themselves.
+ */
+static DECLARE_WAIT_QUEUE_HEAD(slow_work_queue_waits_for_occupation);
+static DECLARE_WAIT_QUEUE_HEAD(vslow_work_queue_waits_for_occupation);
 
 /*
  * The thread controls.  A variable used to signal to the threads that they
@@ -126,6 +158,20 @@ static DECLARE_COMPLETION(slow_work_last_thread_exited);
 static int slow_work_user_count;
 static DEFINE_MUTEX(slow_work_user_lock);
 
+static inline int slow_work_get_ref(struct slow_work *work)
+{
+	if (work->ops->get_ref)
+		return work->ops->get_ref(work);
+
+	return 0;
+}
+
+static inline void slow_work_put_ref(struct slow_work *work)
+{
+	if (work->ops->put_ref)
+		work->ops->put_ref(work);
+}
+
 /*
  * Calculate the maximum number of active threads in the pool that are
  * permitted to process very slow work items.
@@ -149,8 +195,11 @@ static unsigned slow_work_calc_vsmax(void)
  * Attempt to execute stuff queued on a slow thread.  Return true if we managed
  * it, false if there was nothing to do.
  */
-static bool slow_work_execute(void)
+static noinline bool slow_work_execute(int id)
 {
+#ifdef CONFIG_MODULES
+	struct module *module;
+#endif
 	struct slow_work *work = NULL;
 	unsigned vsmax;
 	bool very_slow;
@@ -186,6 +235,16 @@ static bool slow_work_execute(void)
 	} else {
 		very_slow = false; /* avoid the compiler warning */
 	}
+
+#ifdef CONFIG_MODULES
+	if (work)
+		slow_work_thread_processing[id] = work->owner;
+#endif
+	if (work) {
+		slow_work_mark_time(work);
+		slow_work_begin_exec(id, work);
+	}
+
 	spin_unlock_irq(&slow_work_queue_lock);
 
 	if (!work)
@@ -194,12 +253,19 @@ 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 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);
+
+	slow_work_end_exec(id, work);
+
 	/* 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
@@ -219,7 +285,18 @@ static bool slow_work_execute(void)
 		spin_unlock_irq(&slow_work_queue_lock);
 	}
 
-	work->ops->put_ref(work);
+	/* sort out the race between module unloading and put_ref() */
+	slow_work_put_ref(work);
+
+#ifdef CONFIG_MODULES
+	module = slow_work_thread_processing[id];
+	slow_work_thread_processing[id] = NULL;
+	smp_mb();
+	if (slow_work_unreg_work_item == work ||
+	    slow_work_unreg_module == module)
+		wake_up_all(&slow_work_unreg_wq);
+#endif
+
 	return true;
 
 auto_requeue:
@@ -227,15 +304,61 @@ auto_requeue:
 	 * - we transfer our ref on the item back to the appropriate queue
 	 * - don't wake another thread up as we're awake already
 	 */
+	slow_work_mark_time(work);
 	if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags))
 		list_add_tail(&work->link, &vslow_work_queue);
 	else
 		list_add_tail(&work->link, &slow_work_queue);
 	spin_unlock_irq(&slow_work_queue_lock);
+	slow_work_thread_processing[id] = NULL;
 	return true;
 }
 
 /**
+ * slow_work_sleep_till_thread_needed - Sleep till thread needed by other work
+ * work: The work item under execution that wants to sleep
+ * _timeout: Scheduler sleep timeout
+ *
+ * Allow a requeueable work item to sleep on a slow-work processor thread until
+ * that thread is needed to do some other work or the sleep is interrupted by
+ * some other event.
+ *
+ * The caller must set up a wake up event before calling this and must have set
+ * the appropriate sleep mode (such as TASK_UNINTERRUPTIBLE) and tested its own
+ * condition before calling this function as no test is made here.
+ *
+ * False is returned if there is nothing on the queue; true is returned if the
+ * work item should be requeued
+ */
+bool slow_work_sleep_till_thread_needed(struct slow_work *work,
+					signed long *_timeout)
+{
+	wait_queue_head_t *wfo_wq;
+	struct list_head *queue;
+
+	DEFINE_WAIT(wait);
+
+	if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {
+		wfo_wq = &vslow_work_queue_waits_for_occupation;
+		queue = &vslow_work_queue;
+	} else {
+		wfo_wq = &slow_work_queue_waits_for_occupation;
+		queue = &slow_work_queue;
+	}
+
+	if (!list_empty(queue))
+		return true;
+
+	add_wait_queue_exclusive(wfo_wq, &wait);
+	if (list_empty(queue))
+		*_timeout = schedule_timeout(*_timeout);
+	finish_wait(wfo_wq, &wait);
+
+	return !list_empty(queue);
+}
+EXPORT_SYMBOL(slow_work_sleep_till_thread_needed);
+
+/**
  * slow_work_enqueue - Schedule a slow work item for processing
  * @work: The work item to queue
  *
@@ -260,16 +383,22 @@ 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)
 {
+	wait_queue_head_t *wfo_wq;
+	struct list_head *queue;
 	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);
 	BUG_ON(!work->ops);
-	BUG_ON(!work->ops->get_ref);
 
 	/* when honouring an enqueue request, we only promise that we will run
 	 * the work function in the future; we do not promise to run it once
@@ -280,8 +409,19 @@ int slow_work_enqueue(struct slow_work *work)
 	 * maintaining our promise
 	 */
 	if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) {
+		if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {
+			wfo_wq = &vslow_work_queue_waits_for_occupation;
+			queue = &vslow_work_queue;
+		} else {
+			wfo_wq = &slow_work_queue_waits_for_occupation;
+			queue = &slow_work_queue;
+		}
+
 		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
 		 *
@@ -299,25 +439,221 @@ 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 (work->ops->get_ref(work) < 0)
-				goto cant_get_ref;
-			if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags))
-				list_add_tail(&work->link, &vslow_work_queue);
-			else
-				list_add_tail(&work->link, &slow_work_queue);
+			ret = slow_work_get_ref(work);
+			if (ret < 0)
+				goto failed;
+			slow_work_mark_time(work);
+			list_add_tail(&work->link, queue);
 			wake_up(&slow_work_thread_wq);
+
+			/* if someone who could be requeued is sleeping on a
+			 * thread, then ask them to yield their thread */
+			if (work->link.prev == queue)
+				wake_up(wfo_wq);
 		}
 
 		spin_unlock_irqrestore(&slow_work_queue_lock, flags);
 	}
 	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);
+	smp_mb();
+
+	/* if the work item is a delayed work item with an active timer, we
+	 * need to wait for the timer to finish _before_ getting the spinlock,
+	 * lest we deadlock against the timer routine
+	 *
+	 * the timer routine will leave DELAYED set if it notices the
+	 * CANCELLING flag in time
+	 */
+	if (test_bit(SLOW_WORK_DELAYED, &work->flags)) {
+		struct delayed_slow_work *dwork =
+			container_of(work, struct delayed_slow_work, work);
+		del_timer_sync(&dwork->timer);
+	}
+
+	spin_lock_irq(&slow_work_queue_lock);
+
+	if (test_bit(SLOW_WORK_DELAYED, &work->flags)) {
+		/* the timer routine aborted or never happened, so we are left
+		 * holding the timer's reference on the item and should just
+		 * drop the pending flag and wait for any ongoing execution to
+		 * finish */
+		struct delayed_slow_work *dwork =
+			container_of(work, struct delayed_slow_work, work);
+
+		BUG_ON(timer_pending(&dwork->timer));
+		BUG_ON(!list_empty(&work->link));
+
+		clear_bit(SLOW_WORK_DELAYED, &work->flags);
+		put = true;
+		clear_bit(SLOW_WORK_PENDING, &work->flags);
+
+	} else 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);
+
+/*
+ * Handle expiry of the delay timer, indicating that a delayed slow work item
+ * should now be queued if not cancelled
+ */
+static void delayed_slow_work_timer(unsigned long data)
+{
+	wait_queue_head_t *wfo_wq;
+	struct list_head *queue;
+	struct slow_work *work = (struct slow_work *) data;
+	unsigned long flags;
+	bool queued = false, put = false, first = false;
+
+	if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) {
+		wfo_wq = &vslow_work_queue_waits_for_occupation;
+		queue = &vslow_work_queue;
+	} else {
+		wfo_wq = &slow_work_queue_waits_for_occupation;
+		queue = &slow_work_queue;
+	}
+
+	spin_lock_irqsave(&slow_work_queue_lock, flags);
+	if (likely(!test_bit(SLOW_WORK_CANCELLING, &work->flags))) {
+		clear_bit(SLOW_WORK_DELAYED, &work->flags);
+
+		if (test_bit(SLOW_WORK_EXECUTING, &work->flags)) {
+			/* we discard the reference the timer was holding in
+			 * favour of the one the executor holds */
+			set_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags);
+			put = true;
+		} else {
+			slow_work_mark_time(work);
+			list_add_tail(&work->link, queue);
+			queued = true;
+			if (work->link.prev == queue)
+				first = true;
+		}
+	}
+
+	spin_unlock_irqrestore(&slow_work_queue_lock, flags);
+	if (put)
+		slow_work_put_ref(work);
+	if (first)
+		wake_up(wfo_wq);
+	if (queued)
+		wake_up(&slow_work_thread_wq);
+}
+
+/**
+ * delayed_slow_work_enqueue - Schedule a delayed slow work item for processing
+ * @dwork: The delayed work item to queue
+ * @delay: When to start executing the work, in jiffies from now
+ *
+ * This is similar to slow_work_enqueue(), but it adds a delay before the work
+ * is actually queued for processing.
+ *
+ * The item can have delayed processing requested on it whilst it is being
+ * executed.  The delay will begin immediately, and if it expires before the
+ * item finishes executing, the item will be placed back on the queue when it
+ * has done executing.
+ */
+int delayed_slow_work_enqueue(struct delayed_slow_work *dwork,
+			      unsigned long delay)
+{
+	struct slow_work *work = &dwork->work;
+	unsigned long flags;
+	int ret;
+
+	if (delay == 0)
+		return slow_work_enqueue(&dwork->work);
+
+	BUG_ON(slow_work_user_count <= 0);
+	BUG_ON(!work);
+	BUG_ON(!work->ops);
+
+	if (test_bit(SLOW_WORK_CANCELLING, &work->flags))
+		return -ECANCELED;
+
+	if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) {
+		spin_lock_irqsave(&slow_work_queue_lock, flags);
+
+		if (test_bit(SLOW_WORK_CANCELLING, &work->flags))
+			goto cancelled;
+
+		/* the timer holds a reference whilst it is pending */
+		ret = work->ops->get_ref(work);
+		if (ret < 0)
+			goto cant_get_ref;
+
+		if (test_and_set_bit(SLOW_WORK_DELAYED, &work->flags))
+			BUG();
+		dwork->timer.expires = jiffies + delay;
+		dwork->timer.data = (unsigned long) work;
+		dwork->timer.function = delayed_slow_work_timer;
+		add_timer(&dwork->timer);
+
+		spin_unlock_irqrestore(&slow_work_queue_lock, flags);
+	}
+
+	return 0;
+
+cancelled:
+	ret = -ECANCELED;
+cant_get_ref:
+	spin_unlock_irqrestore(&slow_work_queue_lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL(delayed_slow_work_enqueue);
+
 /*
  * Schedule a cull of the thread pool at some time in the near future
  */
@@ -368,13 +704,23 @@ static inline bool slow_work_available(int vsmax)
  */
 static int slow_work_thread(void *_data)
 {
-	int vsmax;
+	int vsmax, id;
 
 	DEFINE_WAIT(wait);
 
 	set_freezable();
 	set_user_nice(current, -5);
 
+	/* allocate ourselves an ID */
+	spin_lock_irq(&slow_work_queue_lock);
+	id = find_first_zero_bit(slow_work_ids, SLOW_WORK_THREAD_LIMIT);
+	BUG_ON(id < 0 || id >= SLOW_WORK_THREAD_LIMIT);
+	__set_bit(id, slow_work_ids);
+	slow_work_set_thread_pid(id, current->pid);
+	spin_unlock_irq(&slow_work_queue_lock);
+
+	sprintf(current->comm, "kslowd%03u", id);
+
 	for (;;) {
 		vsmax = vslow_work_proportion;
 		vsmax *= atomic_read(&slow_work_thread_count);
@@ -395,7 +741,7 @@ static int slow_work_thread(void *_data)
 		vsmax *= atomic_read(&slow_work_thread_count);
 		vsmax /= 100;
 
-		if (slow_work_available(vsmax) && slow_work_execute()) {
+		if (slow_work_available(vsmax) && slow_work_execute(id)) {
 			cond_resched();
 			if (list_empty(&slow_work_queue) &&
 			    list_empty(&vslow_work_queue) &&
@@ -412,6 +758,11 @@ static int slow_work_thread(void *_data)
 			break;
 	}
 
+	spin_lock_irq(&slow_work_queue_lock);
+	slow_work_set_thread_pid(id, 0);
+	__clear_bit(id, slow_work_ids);
+	spin_unlock_irq(&slow_work_queue_lock);
+
 	if (atomic_dec_and_test(&slow_work_thread_count))
 		complete_and_exit(&slow_work_last_thread_exited, 0);
 	return 0;
@@ -427,21 +778,6 @@ static void slow_work_cull_timeout(unsigned long data)
 }
 
 /*
- * Get a reference on slow work thread starter
- */
-static int slow_work_new_thread_get_ref(struct slow_work *work)
-{
-	return 0;
-}
-
-/*
- * Drop a reference on slow work thread starter
- */
-static void slow_work_new_thread_put_ref(struct slow_work *work)
-{
-}
-
-/*
  * Start a new slow work thread
  */
 static void slow_work_new_thread_execute(struct slow_work *work)
@@ -475,9 +811,11 @@ static void slow_work_new_thread_execute(struct slow_work *work)
 }
 
 static const struct slow_work_ops slow_work_new_thread_ops = {
-	.get_ref	= slow_work_new_thread_get_ref,
-	.put_ref	= slow_work_new_thread_put_ref,
+	.owner		= THIS_MODULE,
 	.execute	= slow_work_new_thread_execute,
+#ifdef CONFIG_SLOW_WORK_PROC
+	.desc		= slow_work_new_thread_desc,
+#endif
 };
 
 /*
@@ -546,12 +884,13 @@ static int slow_work_max_threads_sysctl(struct ctl_table *table, int write,
 
 /**
  * slow_work_register_user - Register a user of the facility
+ * @module: The module about to make use of the facility
  *
  * Register a user of the facility, starting up the initial threads if there
  * aren't any other users at this point.  This will return 0 if successful, or
  * an error if not.
  */
-int slow_work_register_user(void)
+int slow_work_register_user(struct module *module)
 {
 	struct task_struct *p;
 	int loop;
@@ -598,14 +937,79 @@ error:
 }
 EXPORT_SYMBOL(slow_work_register_user);
 
+/*
+ * wait for all outstanding items from the calling module to complete
+ * - note that more items may be queued whilst we're waiting
+ */
+static void slow_work_wait_for_items(struct module *module)
+{
+	DECLARE_WAITQUEUE(myself, current);
+	struct slow_work *work;
+	int loop;
+
+	mutex_lock(&slow_work_unreg_sync_lock);
+	add_wait_queue(&slow_work_unreg_wq, &myself);
+
+	for (;;) {
+		spin_lock_irq(&slow_work_queue_lock);
+
+		/* first of all, we wait for the last queued item in each list
+		 * to be processed */
+		list_for_each_entry_reverse(work, &vslow_work_queue, link) {
+			if (work->owner == module) {
+				set_current_state(TASK_UNINTERRUPTIBLE);
+				slow_work_unreg_work_item = work;
+				goto do_wait;
+			}
+		}
+		list_for_each_entry_reverse(work, &slow_work_queue, link) {
+			if (work->owner == module) {
+				set_current_state(TASK_UNINTERRUPTIBLE);
+				slow_work_unreg_work_item = work;
+				goto do_wait;
+			}
+		}
+
+		/* then we wait for the items being processed to finish */
+		slow_work_unreg_module = module;
+		smp_mb();
+		for (loop = 0; loop < SLOW_WORK_THREAD_LIMIT; loop++) {
+			if (slow_work_thread_processing[loop] == module)
+				goto do_wait;
+		}
+		spin_unlock_irq(&slow_work_queue_lock);
+		break; /* okay, we're done */
+
+	do_wait:
+		spin_unlock_irq(&slow_work_queue_lock);
+		schedule();
+		slow_work_unreg_work_item = NULL;
+		slow_work_unreg_module = NULL;
+	}
+
+	remove_wait_queue(&slow_work_unreg_wq, &myself);
+	mutex_unlock(&slow_work_unreg_sync_lock);
+}
+
 /**
  * slow_work_unregister_user - Unregister a user of the facility
+ * @module: The module whose items should be cleared
  *
  * Unregister a user of the facility, killing all the threads if this was the
  * last one.
+ *
+ * This waits for all the work items belonging to the nominated module to go
+ * away before proceeding.
  */
-void slow_work_unregister_user(void)
+void slow_work_unregister_user(struct module *module)
 {
+	/* first of all, wait for all outstanding items from the calling module
+	 * to complete */
+	if (module)
+		slow_work_wait_for_items(module);
+
+	/* then we can actually go about shutting down the facility if need
+	 * be */
 	mutex_lock(&slow_work_user_lock);
 
 	BUG_ON(slow_work_user_count <= 0);
@@ -639,6 +1043,10 @@ static int __init init_slow_work(void)
 	if (slow_work_max_max_threads < nr_cpus * 2)
 		slow_work_max_max_threads = nr_cpus * 2;
 #endif
+#ifdef CONFIG_SLOW_WORK_PROC
+	proc_create("slow_work_rq", S_IFREG | 0400, NULL,
+		    &slow_work_runqueue_fops);
+#endif
 	return 0;
 }