4 files changed, 769 insertions, 43 deletions

diff --git a/kernel/Makefile b/kernel/Makefile
index b8d4cd8ac0b9..d7c13d249b2d 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -94,6 +94,7 @@ obj-$(CONFIG_X86_DS) += trace/
 obj-$(CONFIG_RING_BUFFER) += trace/
 obj-$(CONFIG_SMP) += sched_cpupri.o
 obj-$(CONFIG_SLOW_WORK) += slow-work.o
+obj-$(CONFIG_SLOW_WORK_DEBUG) += slow-work-debugfs.o
 obj-$(CONFIG_PERF_EVENTS) += perf_event.o
 
 ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y)
diff --git a/kernel/slow-work-debugfs.c b/kernel/slow-work-debugfs.c
new file mode 100644
index 000000000000..e45c43645298
--- /dev/null
+++ b/kernel/slow-work-debugfs.c
@@ -0,0 +1,227 @@
+/* Slow work debugging
+ *
+ * Copyright (C) 2009 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/module.h>
+#include <linux/slow-work.h>
+#include <linux/fs.h>
+#include <linux/time.h>
+#include <linux/seq_file.h>
+#include "slow-work.h"
+
+#define ITERATOR_SHIFT          (BITS_PER_LONG - 4)
+#define ITERATOR_SELECTOR       (0xfUL << ITERATOR_SHIFT)
+#define ITERATOR_COUNTER        (~ITERATOR_SELECTOR)
+
+void slow_work_new_thread_desc(struct slow_work *work, struct seq_file *m)
+{
+        seq_puts(m, "Slow-work: New thread");
+}
+
+/*
+ * Render the time mark field on a work item into a 5-char time with units plus
+ * a space
+ */
+static void slow_work_print_mark(struct seq_file *m, struct slow_work *work)
+{
+        struct timespec now, diff;
+
+        now = CURRENT_TIME;
+        diff = timespec_sub(now, work->mark);
+
+        if (diff.tv_sec < 0)
+                seq_puts(m, "  -ve ");
+        else if (diff.tv_sec == 0 && diff.tv_nsec < 1000)
+                seq_printf(m, "%3luns ", diff.tv_nsec);
+        else if (diff.tv_sec == 0 && diff.tv_nsec < 1000000)
+                seq_printf(m, "%3luus ", diff.tv_nsec / 1000);
+        else if (diff.tv_sec == 0 && diff.tv_nsec < 1000000000)
+                seq_printf(m, "%3lums ", diff.tv_nsec / 1000000);
+        else if (diff.tv_sec <= 1)
+                seq_puts(m, "   1s ");
+        else if (diff.tv_sec < 60)
+                seq_printf(m, "%4lus ", diff.tv_sec);
+        else if (diff.tv_sec < 60 * 60)
+                seq_printf(m, "%4lum ", diff.tv_sec / 60);
+        else if (diff.tv_sec < 60 * 60 * 24)
+                seq_printf(m, "%4luh ", diff.tv_sec / 3600);
+        else
+                seq_puts(m, "exces ");
+}
+
+/*
+ * Describe a slow work item for debugfs
+ */
+static int slow_work_runqueue_show(struct seq_file *m, void *v)
+{
+        struct slow_work *work;
+        struct list_head *p = v;
+        unsigned long id;
+
+        switch ((unsigned long) v) {
+        case 1:
+                seq_puts(m, "THR PID   ITEM ADDR        FL MARK  DESC\n");
+                return 0;
+        case 2:
+                seq_puts(m, "=== ===== ================ == ===== ==========\n");
+                return 0;
+
+        case 3 ... 3 + SLOW_WORK_THREAD_LIMIT - 1:
+                id = (unsigned long) v - 3;
+
+                read_lock(&slow_work_execs_lock);
+                work = slow_work_execs[id];
+                if (work) {
+                        smp_read_barrier_depends();
+
+                        seq_printf(m, "%3lu %5d %16p %2lx ",
+                                   id, slow_work_pids[id], work, work->flags);
+                        slow_work_print_mark(m, work);
+
+                        if (work->ops->desc)
+                                work->ops->desc(work, m);
+                        seq_putc(m, '\n');
+                }
+                read_unlock(&slow_work_execs_lock);
+                return 0;
+
+        default:
+                work = list_entry(p, struct slow_work, link);
+                seq_printf(m, "%3s     - %16p %2lx ",
+                           work->flags & SLOW_WORK_VERY_SLOW ? "vsq" : "sq",
+                           work, work->flags);
+                slow_work_print_mark(m, work);
+
+                if (work->ops->desc)
+                        work->ops->desc(work, m);
+                seq_putc(m, '\n');
+                return 0;
+        }
+}
+
+/*
+ * map the iterator to a work item
+ */
+static void *slow_work_runqueue_index(struct seq_file *m, loff_t *_pos)
+{
+        struct list_head *p;
+        unsigned long count, id;
+
+        switch (*_pos >> ITERATOR_SHIFT) {
+        case 0x0:
+                if (*_pos == 0)
+                        *_pos = 1;
+                if (*_pos < 3)
+                        return (void *)(unsigned long) *_pos;
+                if (*_pos < 3 + SLOW_WORK_THREAD_LIMIT)
+                        for (id = *_pos - 3;
+                             id < SLOW_WORK_THREAD_LIMIT;
+                             id++, (*_pos)++)
+                                if (slow_work_execs[id])
+                                        return (void *)(unsigned long) *_pos;
+                *_pos = 0x1UL << ITERATOR_SHIFT;
+
+        case 0x1:
+                count = *_pos & ITERATOR_COUNTER;
+                list_for_each(p, &slow_work_queue) {
+                        if (count == 0)
+                                return p;
+                        count--;
+                }
+                *_pos = 0x2UL << ITERATOR_SHIFT;
+
+        case 0x2:
+                count = *_pos & ITERATOR_COUNTER;
+                list_for_each(p, &vslow_work_queue) {
+                        if (count == 0)
+                                return p;
+                        count--;
+                }
+                *_pos = 0x3UL << ITERATOR_SHIFT;
+
+        default:
+                return NULL;
+        }
+}
+
+/*
+ * set up the iterator to start reading from the first line
+ */
+static void *slow_work_runqueue_start(struct seq_file *m, loff_t *_pos)
+{
+        spin_lock_irq(&slow_work_queue_lock);
+        return slow_work_runqueue_index(m, _pos);
+}
+
+/*
+ * move to the next line
+ */
+static void *slow_work_runqueue_next(struct seq_file *m, void *v, loff_t *_pos)
+{
+        struct list_head *p = v;
+        unsigned long selector = *_pos >> ITERATOR_SHIFT;
+
+        (*_pos)++;
+        switch (selector) {
+        case 0x0:
+                return slow_work_runqueue_index(m, _pos);
+
+        case 0x1:
+                if (*_pos >> ITERATOR_SHIFT == 0x1) {
+                        p = p->next;
+                        if (p != &slow_work_queue)
+                                return p;
+                }
+                *_pos = 0x2UL << ITERATOR_SHIFT;
+                p = &vslow_work_queue;
+
+        case 0x2:
+                if (*_pos >> ITERATOR_SHIFT == 0x2) {
+                        p = p->next;
+                        if (p != &vslow_work_queue)
+                                return p;
+                }
+                *_pos = 0x3UL << ITERATOR_SHIFT;
+
+        default:
+                return NULL;
+        }
+}
+
+/*
+ * clean up after reading
+ */
+static void slow_work_runqueue_stop(struct seq_file *m, void *v)
+{
+        spin_unlock_irq(&slow_work_queue_lock);
+}
+
+static const struct seq_operations slow_work_runqueue_ops = {
+        .start          = slow_work_runqueue_start,
+        .stop           = slow_work_runqueue_stop,
+        .next           = slow_work_runqueue_next,
+        .show           = slow_work_runqueue_show,
+};
+
+/*
+ * open "/sys/kernel/debug/slow_work/runqueue" to list queue contents
+ */
+static int slow_work_runqueue_open(struct inode *inode, struct file *file)
+{
+        return seq_open(file, &slow_work_runqueue_ops);
+}
+
+const struct file_operations slow_work_runqueue_fops = {
+        .owner          = THIS_MODULE,
+        .open           = slow_work_runqueue_open,
+        .read           = seq_read,
+        .llseek         = seq_lseek,
+        .release        = seq_release,
+};
diff --git a/kernel/slow-work.c b/kernel/slow-work.c
index 0d31135efbf4..00889bd3c590 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/debugfs.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 +95,56 @@ 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);
+
+static void slow_work_set_thread_processing(int id, struct slow_work *work)
+{
+        if (work)
+                slow_work_thread_processing[id] = work->owner;
+}
+static void slow_work_done_thread_processing(int id, struct slow_work *work)
+{
+        struct module *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);
+}
+static void slow_work_clear_thread_processing(int id)
+{
+        slow_work_thread_processing[id] = NULL;
+}
+#else
+static void slow_work_set_thread_processing(int id, struct slow_work *work) {}
+static void slow_work_done_thread_processing(int id, struct slow_work *work) {}
+static void slow_work_clear_thread_processing(int id) {}
+#endif
+
+/*
+ * Data for tracking currently executing items for indication through /proc
+ */
+#ifdef CONFIG_SLOW_WORK_DEBUG
+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 +152,18 @@ 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 +182,20 @@ 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.
@@ -149,7 +219,7 @@ 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)
 {
         struct slow_work *work = NULL;
         unsigned vsmax;
@@ -186,6 +256,13 @@ static bool slow_work_execute(void)
         } else {
                 very_slow = false; /* avoid the compiler warning */
         }
+
+        slow_work_set_thread_processing(id, work);
+        if (work) {
+                slow_work_mark_time(work);
+                slow_work_begin_exec(id, work);
+        }
+
         spin_unlock_irq(&slow_work_queue_lock);
 
         if (!work)
@@ -194,12 +271,19 @@ 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 +303,10 @@ 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);
+        slow_work_done_thread_processing(id, work);
+
         return true;
 
 auto_requeue:
@@ -227,15 +314,61 @@ 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_clear_thread_processing(id);
         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 +393,22 @@ 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 +419,19 @@ 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 +449,221 @@ 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 +714,23 @@ 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 +751,7 @@ 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 +768,11 @@ 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 +788,6 @@ 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 +821,11 @@ 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_DEBUG
+        .desc           = slow_work_new_thread_desc,
+#endif
 };
 
 /*
@@ -546,12 +894,13 @@ 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 +947,81 @@ 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)
+{
+#ifdef CONFIG_MODULES
+        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);
+#endif /* CONFIG_MODULES */
+}
+
 /**
  * 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 +1055,16 @@ 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_DEBUG
+        {
+                struct dentry *dbdir;
+
+                dbdir = debugfs_create_dir("slow_work", NULL);
+                if (dbdir && !IS_ERR(dbdir))
+                        debugfs_create_file("runqueue", S_IFREG | 0400, dbdir,
+                                            NULL, &slow_work_runqueue_fops);
+        }
+#endif
         return 0;
 }
 
diff --git a/kernel/slow-work.h b/kernel/slow-work.h
new file mode 100644
index 000000000000..321f3c59d732
--- /dev/null
+++ b/kernel/slow-work.h
@@ -0,0 +1,72 @@
+/* Slow work private definitions
+ *
+ * Copyright (C) 2009 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#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 */
+
+#define SLOW_WORK_THREAD_LIMIT  255     /* abs maximum number of slow-work threads */
+
+/*
+ * slow-work.c
+ */
+#ifdef CONFIG_SLOW_WORK_DEBUG
+extern struct slow_work *slow_work_execs[];
+extern pid_t slow_work_pids[];
+extern rwlock_t slow_work_execs_lock;
+#endif
+
+extern struct list_head slow_work_queue;
+extern struct list_head vslow_work_queue;
+extern spinlock_t slow_work_queue_lock;
+
+/*
+ * slow-work-debugfs.c
+ */
+#ifdef CONFIG_SLOW_WORK_DEBUG
+extern const struct file_operations slow_work_runqueue_fops;
+
+extern void slow_work_new_thread_desc(struct slow_work *, struct seq_file *);
+#endif
+
+/*
+ * Helper functions
+ */
+static inline void slow_work_set_thread_pid(int id, pid_t pid)
+{
+#ifdef CONFIG_SLOW_WORK_PROC
+        slow_work_pids[id] = pid;
+#endif
+}
+
+static inline void slow_work_mark_time(struct slow_work *work)
+{
+#ifdef CONFIG_SLOW_WORK_PROC
+        work->mark = CURRENT_TIME;
+#endif
+}
+
+static inline void slow_work_begin_exec(int id, struct slow_work *work)
+{
+#ifdef CONFIG_SLOW_WORK_PROC
+        slow_work_execs[id] = work;
+#endif
+}
+
+static inline void slow_work_end_exec(int id, struct slow_work *work)
+{
+#ifdef CONFIG_SLOW_WORK_PROC
+        write_lock(&slow_work_execs_lock);
+        slow_work_execs[id] = NULL;
+        write_unlock(&slow_work_execs_lock);
+#endif
+}