WorkStruct: Merge the pending bit into the wq_data pointer

Reclaim a word from the size of the work_struct by folding the pending bit and
the wq_data pointer together.  This shouldn't cause misalignment problems as
all pointers should be at least 4-byte aligned.

Signed-Off-By: David Howells <dhowells@redhat.com>

3 files changed, 57 insertions, 15 deletions

diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index 5a14fac13b12..aa1eb4466f9d 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -1868,7 +1868,7 @@ static void show_floppy(void)
         printk("fdc_busy=%lu\n", fdc_busy);
         if (do_floppy)
                 printk("do_floppy=%p\n", do_floppy);
-        if (floppy_work.pending)
+        if (work_pending(&floppy_work))
                 printk("floppy_work.func=%p\n", floppy_work.func);
         if (timer_pending(&fd_timer))
                 printk("fd_timer.function=%p\n", fd_timer.function);
@@ -4498,7 +4498,7 @@ static void floppy_release_irq_and_dma(void)
                 printk("floppy timer still active:%s\n", timeout_message);
         if (timer_pending(&fd_timer))
                 printk("auxiliary floppy timer still active\n");
-        if (floppy_work.pending)
+        if (work_pending(&floppy_work))
                 printk("work still pending\n");
 #endif
         old_fdc = fdc;
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index cef40b22ff9a..ecc017d24cf3 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -14,11 +14,15 @@ struct workqueue_struct;
 typedef void (*work_func_t)(void *data);
 
 struct work_struct {
-        unsigned long pending;
+        /* the first word is the work queue pointer and the pending flag
+         * rolled into one */
+        unsigned long management;
+#define WORK_STRUCT_PENDING 0           /* T if work item pending execution */
+#define WORK_STRUCT_FLAG_MASK (3UL)
+#define WORK_STRUCT_WQ_DATA_MASK (~WORK_STRUCT_FLAG_MASK)
         struct list_head entry;
         work_func_t func;
         void *data;
-        void *wq_data;
 };
 
 struct delayed_work {
@@ -65,7 +69,7 @@ struct execute_work {
 #define INIT_WORK(_work, _func, _data)                          \
         do {                                                    \
                 INIT_LIST_HEAD(&(_work)->entry);                \
-                (_work)->pending = 0;                           \
+                (_work)->management = 0;                        \
                 PREPARE_WORK((_work), (_func), (_data));        \
         } while (0)
 
@@ -75,6 +79,21 @@ struct execute_work {
                 init_timer(&(_work)->timer);                    \
         } while (0)
 
+/**
+ * work_pending - Find out whether a work item is currently pending
+ * @work: The work item in question
+ */
+#define work_pending(work) \
+        test_bit(WORK_STRUCT_PENDING, &(work)->management)
+
+/**
+ * delayed_work_pending - Find out whether a delayable work item is currently
+ * pending
+ * @work: The work item in question
+ */
+#define delayed_work_pending(work) \
+        test_bit(WORK_STRUCT_PENDING, &(work)->work.management)
+
 
 extern struct workqueue_struct *__create_workqueue(const char *name,
                                                     int singlethread);
@@ -115,7 +134,7 @@ static inline int cancel_delayed_work(struct delayed_work *work)
 
         ret = del_timer_sync(&work->timer);
         if (ret)
-                clear_bit(0, &work->work.pending);
+                clear_bit(WORK_STRUCT_PENDING, &work->work.management);
         return ret;
 }
 
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1e9d61ecf762..967479756511 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -80,6 +80,29 @@ static inline int is_single_threaded(struct workqueue_struct *wq)
         return list_empty(&wq->list);
 }
 
+static inline void set_wq_data(struct work_struct *work, void *wq)
+{
+        unsigned long new, old, res;
+
+        /* assume the pending flag is already set and that the task has already
+         * been queued on this workqueue */
+        new = (unsigned long) wq | (1UL << WORK_STRUCT_PENDING);
+        res = work->management;
+        if (res != new) {
+                do {
+                        old = res;
+                        new = (unsigned long) wq;
+                        new |= (old & WORK_STRUCT_FLAG_MASK);
+                        res = cmpxchg(&work->management, old, new);
+                } while (res != old);
+        }
+}
+
+static inline void *get_wq_data(struct work_struct *work)
+{
+        return (void *) (work->management & WORK_STRUCT_WQ_DATA_MASK);
+}
+
 /* Preempt must be disabled. */
 static void __queue_work(struct cpu_workqueue_struct *cwq,
                          struct work_struct *work)
@@ -87,7 +110,7 @@ static void __queue_work(struct cpu_workqueue_struct *cwq,
         unsigned long flags;
 
         spin_lock_irqsave(&cwq->lock, flags);
-        work->wq_data = cwq;
+        set_wq_data(work, cwq);
         list_add_tail(&work->entry, &cwq->worklist);
         cwq->insert_sequence++;
         wake_up(&cwq->more_work);
@@ -108,7 +131,7 @@ int fastcall queue_work(struct workqueue_struct *wq, struct work_struct *work)
 {
         int ret = 0, cpu = get_cpu();
 
-        if (!test_and_set_bit(0, &work->pending)) {
+        if (!test_and_set_bit(WORK_STRUCT_PENDING, &work->management)) {
                 if (unlikely(is_single_threaded(wq)))
                         cpu = singlethread_cpu;
                 BUG_ON(!list_empty(&work->entry));
@@ -123,7 +146,7 @@ EXPORT_SYMBOL_GPL(queue_work);
 static void delayed_work_timer_fn(unsigned long __data)
 {
         struct delayed_work *dwork = (struct delayed_work *)__data;
-        struct workqueue_struct *wq = dwork->work.wq_data;
+        struct workqueue_struct *wq = get_wq_data(&dwork->work);
         int cpu = smp_processor_id();
 
         if (unlikely(is_single_threaded(wq)))
@@ -150,12 +173,12 @@ int fastcall queue_delayed_work(struct workqueue_struct *wq,
         if (delay == 0)
                 return queue_work(wq, work);
 
-        if (!test_and_set_bit(0, &work->pending)) {
+        if (!test_and_set_bit(WORK_STRUCT_PENDING, &work->management)) {
                 BUG_ON(timer_pending(timer));
                 BUG_ON(!list_empty(&work->entry));
 
                 /* This stores wq for the moment, for the timer_fn */
-                work->wq_data = wq;
+                set_wq_data(work, wq);
                 timer->expires = jiffies + delay;
                 timer->data = (unsigned long)dwork;
                 timer->function = delayed_work_timer_fn;
@@ -182,12 +205,12 @@ int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
         struct timer_list *timer = &dwork->timer;
         struct work_struct *work = &dwork->work;
 
-        if (!test_and_set_bit(0, &work->pending)) {
+        if (!test_and_set_bit(WORK_STRUCT_PENDING, &work->management)) {
                 BUG_ON(timer_pending(timer));
                 BUG_ON(!list_empty(&work->entry));
 
                 /* This stores wq for the moment, for the timer_fn */
-                work->wq_data = wq;
+                set_wq_data(work, wq);
                 timer->expires = jiffies + delay;
                 timer->data = (unsigned long)dwork;
                 timer->function = delayed_work_timer_fn;
@@ -223,8 +246,8 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq)
                 list_del_init(cwq->worklist.next);
                 spin_unlock_irqrestore(&cwq->lock, flags);
 
-                BUG_ON(work->wq_data != cwq);
-                clear_bit(0, &work->pending);
+                BUG_ON(get_wq_data(work) != cwq);
+                clear_bit(WORK_STRUCT_PENDING, &work->management);
                 f(data);
 
                 spin_lock_irqsave(&cwq->lock, flags);