[12/17] workqueue: Implement disable/enable for (delayed) work items

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index e15fc77bf2e2..f25915e47efb 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -51,20 +51,23 @@  enum work_bits {
 	 * data contains off-queue information when !WORK_STRUCT_PWQ.
 	 *
 	 * MSB
-	 * [ pool ID ] [ OFFQ flags ] [ STRUCT flags ]
-	 *                 1 bit        4 or 5 bits
+	 * [ pool ID ] [ disable depth ] [ OFFQ flags ] [ STRUCT flags ]
+	 *                  16 bits          1 bit        4 or 5 bits
 	 */
 	WORK_OFFQ_FLAG_SHIFT	= WORK_STRUCT_FLAG_BITS,
 	WORK_OFFQ_CANCELING_BIT = WORK_OFFQ_FLAG_SHIFT,
 	WORK_OFFQ_FLAG_END,
 	WORK_OFFQ_FLAG_BITS	= WORK_OFFQ_FLAG_END - WORK_OFFQ_FLAG_SHIFT,
 
+	WORK_OFFQ_DISABLE_SHIFT	= WORK_OFFQ_FLAG_SHIFT + WORK_OFFQ_FLAG_BITS,
+	WORK_OFFQ_DISABLE_BITS	= 16,
+
 	/*
 	 * When a work item is off queue, the high bits encode off-queue flags
 	 * and the last pool it was on. Cap pool ID to 31 bits and use the
 	 * highest number to indicate that no pool is associated.
 	 */
-	WORK_OFFQ_POOL_SHIFT	= WORK_OFFQ_FLAG_SHIFT + WORK_OFFQ_FLAG_BITS,
+	WORK_OFFQ_POOL_SHIFT	= WORK_OFFQ_DISABLE_SHIFT + WORK_OFFQ_DISABLE_BITS,
 	WORK_OFFQ_LEFT		= BITS_PER_LONG - WORK_OFFQ_POOL_SHIFT,
 	WORK_OFFQ_POOL_BITS	= WORK_OFFQ_LEFT <= 31 ? WORK_OFFQ_LEFT : 31,
 };
@@ -98,6 +101,7 @@  enum wq_misc_consts {
 /* Convenience constants - of type 'unsigned long', not 'enum'! */
 #define WORK_OFFQ_CANCELING	(1ul << WORK_OFFQ_CANCELING_BIT)
 #define WORK_OFFQ_FLAG_MASK	(((1ul << WORK_OFFQ_FLAG_BITS) - 1) << WORK_OFFQ_FLAG_SHIFT)
+#define WORK_OFFQ_DISABLE_MASK	(((1ul << WORK_OFFQ_DISABLE_BITS) - 1) << WORK_OFFQ_DISABLE_SHIFT)
 #define WORK_OFFQ_POOL_NONE	((1ul << WORK_OFFQ_POOL_BITS) - 1)
 #define WORK_STRUCT_NO_POOL	(WORK_OFFQ_POOL_NONE << WORK_OFFQ_POOL_SHIFT)
 #define WORK_STRUCT_PWQ_MASK	(~((1ul << WORK_STRUCT_PWQ_SHIFT) - 1))
@@ -556,6 +560,14 @@  extern bool flush_delayed_work(struct delayed_work *dwork);
 extern bool cancel_delayed_work(struct delayed_work *dwork);
 extern bool cancel_delayed_work_sync(struct delayed_work *dwork);
 
+extern bool disable_work(struct work_struct *work);
+extern bool disable_work_sync(struct work_struct *work);
+extern bool enable_work(struct work_struct *work);
+
+extern bool disable_delayed_work(struct delayed_work *dwork);
+extern bool disable_delayed_work_sync(struct delayed_work *dwork);
+extern bool enable_delayed_work(struct delayed_work *dwork);
+
 extern bool flush_rcu_work(struct rcu_work *rwork);
 
 extern void workqueue_set_max_active(struct workqueue_struct *wq,
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index e8f310aa16d6..87e40e6e14cb 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -98,6 +98,7 @@  enum worker_flags {
 
 enum work_cancel_flags {
 	WORK_CANCEL_DELAYED	= 1 << 0,	/* canceling a delayed_work */
+	WORK_CANCEL_DISABLE	= 1 << 1,	/* canceling to disable */
 };
 
 enum wq_internal_consts {
@@ -393,6 +394,7 @@  struct wq_pod_type {
 
 struct work_offq_data {
 	u32			pool_id;
+	u32			disable;
 	u32			flags;
 };
 
@@ -903,12 +905,15 @@  static void work_offqd_unpack(struct work_offq_data *offqd, unsigned long data)
 
 	offqd->pool_id = shift_and_mask(data, WORK_OFFQ_POOL_SHIFT,
 					WORK_OFFQ_POOL_BITS);
+	offqd->disable = shift_and_mask(data, WORK_OFFQ_DISABLE_SHIFT,
+					WORK_OFFQ_DISABLE_BITS);
 	offqd->flags = data & WORK_OFFQ_FLAG_MASK;
 }
 
 static unsigned long work_offqd_pack_flags(struct work_offq_data *offqd)
 {
-	return (unsigned long)offqd->flags;
+	return ((unsigned long)offqd->disable << WORK_OFFQ_DISABLE_SHIFT) |
+		((unsigned long)offqd->flags);
 }
 
 static bool work_is_canceling(struct work_struct *work)
@@ -2395,6 +2400,21 @@  static void __queue_work(int cpu, struct workqueue_struct *wq,
 	rcu_read_unlock();
 }
 
+static bool clear_pending_if_disabled(struct work_struct *work)
+{
+	unsigned long data = *work_data_bits(work);
+	struct work_offq_data offqd;
+
+	if (likely((data & WORK_STRUCT_PWQ) ||
+		   !(data & WORK_OFFQ_DISABLE_MASK)))
+		return false;
+
+	work_offqd_unpack(&offqd, data);
+	set_work_pool_and_clear_pending(work, offqd.pool_id,
+					work_offqd_pack_flags(&offqd));
+	return true;
+}
+
 /**
  * queue_work_on - queue work on specific cpu
  * @cpu: CPU number to execute work on
@@ -2417,7 +2437,8 @@  bool queue_work_on(int cpu, struct workqueue_struct *wq,
 
 	local_irq_save(irq_flags);
 
-	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
+	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)) &&
+	    !clear_pending_if_disabled(work)) {
 		__queue_work(cpu, wq, work);
 		ret = true;
 	}
@@ -2577,7 +2598,8 @@  bool queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
 	/* read the comment in __queue_work() */
 	local_irq_save(irq_flags);
 
-	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
+	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)) &&
+	    !clear_pending_if_disabled(work)) {
 		__queue_delayed_work(cpu, wq, dwork, delay);
 		ret = true;
 	}
@@ -4173,20 +4195,46 @@  bool flush_rcu_work(struct rcu_work *rwork)
 }
 EXPORT_SYMBOL(flush_rcu_work);
 
+static void work_offqd_disable(struct work_offq_data *offqd)
+{
+	const unsigned long max = (1lu << WORK_OFFQ_DISABLE_BITS) - 1;
+
+	if (likely(offqd->disable < max))
+		offqd->disable++;
+	else
+		WARN_ONCE(true, "workqueue: work disable count overflowed\n");
+}
+
+static void work_offqd_enable(struct work_offq_data *offqd)
+{
+	if (likely(offqd->disable > 0))
+		offqd->disable--;
+	else
+		WARN_ONCE(true, "workqueue: work disable count underflowed\n");
+}
+
 static bool __cancel_work(struct work_struct *work, u32 cflags)
 {
 	struct work_offq_data offqd;
 	unsigned long irq_flags;
 	int ret;
 
-	do {
-		ret = try_to_grab_pending(work, cflags, &irq_flags);
-	} while (unlikely(ret == -EAGAIN));
+	if (cflags & WORK_CANCEL_DISABLE) {
+		ret = work_grab_pending(work, cflags, &irq_flags);
+	} else {
+		do {
+			ret = try_to_grab_pending(work, cflags, &irq_flags);
+		} while (unlikely(ret == -EAGAIN));
 
-	if (unlikely(ret < 0))
-		return false;
+		if (unlikely(ret < 0))
+			return false;
+	}
 
 	work_offqd_unpack(&offqd, *work_data_bits(work));
+
+	if (cflags & WORK_CANCEL_DISABLE)
+		work_offqd_disable(&offqd);
+
 	set_work_pool_and_clear_pending(work, offqd.pool_id,
 					work_offqd_pack_flags(&offqd));
 	local_irq_restore(irq_flags);
@@ -4203,6 +4251,10 @@  static bool __cancel_work_sync(struct work_struct *work, u32 cflags)
 	ret = work_grab_pending(work, cflags, &irq_flags);
 
 	work_offqd_unpack(&offqd, *work_data_bits(work));
+
+	if (cflags & WORK_CANCEL_DISABLE)
+		work_offqd_disable(&offqd);
+
 	offqd.flags |= WORK_OFFQ_CANCELING;
 	set_work_pool_and_keep_pending(work, offqd.pool_id,
 				       work_offqd_pack_flags(&offqd));
@@ -4302,6 +4354,105 @@  bool cancel_delayed_work_sync(struct delayed_work *dwork)
 }
 EXPORT_SYMBOL(cancel_delayed_work_sync);
 
+/**
+ * disable_work - Disable and cancel a work item
+ * @work: work item to disable
+ *
+ * Disable @work by incrementing its disable count and cancel it if currently
+ * pending. As long as the disable count is non-zero, any attempt to queue @work
+ * will fail and return %false. The maximum supported disable depth is 2 to the
+ * power of %WORK_OFFQ_DISABLE_BITS, currently 65536.
+ *
+ * Must be called from a sleepable context. Returns %true if @work was pending,
+ * %false otherwise.
+ */
+bool disable_work(struct work_struct *work)
+{
+	return __cancel_work(work, WORK_CANCEL_DISABLE);
+}
+EXPORT_SYMBOL_GPL(disable_work);
+
+/**
+ * disable_work_sync - Disable, cancel and drain a work item
+ * @work: work item to disable
+ *
+ * Similar to disable_work() but also wait for @work to finish if currently
+ * executing.
+ *
+ * Must be called from a sleepable context. Returns %true if @work was pending,
+ * %false otherwise.
+ */
+bool disable_work_sync(struct work_struct *work)
+{
+	return __cancel_work_sync(work, WORK_CANCEL_DISABLE);
+}
+EXPORT_SYMBOL_GPL(disable_work_sync);
+
+/**
+ * enable_work - Enable a work item
+ * @work: work item to enable
+ *
+ * Undo disable_work[_sync]() by decrementing @work's disable count. @work can
+ * only be queued if its disable count is 0.
+ *
+ * Must be called from a sleepable context. Returns %true if the disable count
+ * reached 0. Otherwise, %false.
+ */
+bool enable_work(struct work_struct *work)
+{
+	struct work_offq_data offqd;
+	unsigned long irq_flags;
+
+	work_grab_pending(work, 0, &irq_flags);
+
+	work_offqd_unpack(&offqd, *work_data_bits(work));
+	work_offqd_enable(&offqd);
+	set_work_pool_and_clear_pending(work, offqd.pool_id,
+					work_offqd_pack_flags(&offqd));
+	local_irq_enable();
+
+	return !offqd.disable;
+}
+EXPORT_SYMBOL_GPL(enable_work);
+
+/**
+ * disable_delayed_work - Disable and cancel a delayed work item
+ * @dwork: delayed work item to disable
+ *
+ * disable_work() for delayed work items.
+ */
+bool disable_delayed_work(struct delayed_work *dwork)
+{
+	return __cancel_work(&dwork->work,
+			     WORK_CANCEL_DELAYED | WORK_CANCEL_DISABLE);
+}
+EXPORT_SYMBOL_GPL(disable_delayed_work);
+
+/**
+ * disable_delayed_work_sync - Disable, cancel and drain a delayed work item
+ * @dwork: delayed work item to disable
+ *
+ * disable_work_sync() for delayed work items.
+ */
+bool disable_delayed_work_sync(struct delayed_work *dwork)
+{
+	return __cancel_work_sync(&dwork->work,
+				  WORK_CANCEL_DELAYED | WORK_CANCEL_DISABLE);
+}
+EXPORT_SYMBOL_GPL(disable_delayed_work_sync);
+
+/**
+ * enable_delayed_work - Enable a delayed work item
+ * @dwork: delayed work item to enable
+ *
+ * enable_work() for delayed work items.
+ */
+bool enable_delayed_work(struct delayed_work *dwork)
+{
+	return enable_work(&dwork->work);
+}
+EXPORT_SYMBOL_GPL(enable_delayed_work);
+
 /**
  * schedule_on_each_cpu - execute a function synchronously on each online CPU
  * @func: the function to call