workqueue: Implement disable/enable for (delayed) work items

While (delayed) work items could be flushed and canceled, there was no way
to prevent them from being queued in the future. While this didn't lead to
functional deficiencies, it sometimes required a bit more effort from the
workqueue users to e.g. sequence shutdown steps with more care.

Workqueue is currently in the process of replacing tasklet which does
support disabling and enabling. The feature is used relatively widely to,
for example, temporarily suppress main path while a control plane operation
(reset or config change) is in progress.

To enable easy conversion of tasklet users and as it seems like an inherent
useful feature, this patch implements disabling and enabling of work items.

- A work item carries 16bit disable count in work->data while not queued.
  The access to the count is synchronized by the PENDING bit like all other
  parts of work->data.

- If the count is non-zero, the work item cannot be queued. Any attempt to
  queue the work item fails and returns %false.

- disable_work[_sync](), enable_work(), disable_delayed_work[_sync]() and
  enable_delayed_work() are added.

v3: enable_work() was using local_irq_enable() instead of
    local_irq_restore() to undo IRQ-disable by work_grab_pending(). This is
    awkward now and will become incorrect as enable_work() will later be
    used from IRQ context too. (Lai)

v2: Lai noticed that queue_work_node() wasn't checking the disable count.
    Fixed. queue_rcu_work() is updated to trigger warning if the inner work
    item is disabled.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>

1 files changed, 15 insertions, 3 deletions

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index ae7ae4a51499..bd80e66298a0 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))
@@ -560,6 +564,14 @@ 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,