workqueue: reimplement work flushing using linked works

A work is linked to the next one by having WORK_STRUCT_LINKED bit set
and these links can be chained.  When a linked work is dispatched to a
worker, all linked works are dispatched to the worker's newly added
->scheduled queue and processed back-to-back.

Currently, as there's only single worker per cwq, having linked works
doesn't make any visible behavior difference.  This change is to
prepare for multiple shared workers per cpu.

Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 8762f62103d8..4f4fdba722c3 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -24,8 +24,9 @@ typedef void (*work_func_t)(struct work_struct *work);
 
 enum {
         WORK_STRUCT_PENDING_BIT = 0,    /* work item is pending execution */
+        WORK_STRUCT_LINKED_BIT  = 1,    /* next work is linked to this one */
 #ifdef CONFIG_DEBUG_OBJECTS_WORK
-        WORK_STRUCT_STATIC_BIT  = 1,    /* static initializer (debugobjects) */
+        WORK_STRUCT_STATIC_BIT  = 2,    /* static initializer (debugobjects) */
         WORK_STRUCT_COLOR_SHIFT = 3,    /* color for workqueue flushing */
 #else
         WORK_STRUCT_COLOR_SHIFT = 2,    /* color for workqueue flushing */
@@ -34,6 +35,7 @@ enum {
         WORK_STRUCT_COLOR_BITS  = 4,
 
         WORK_STRUCT_PENDING     = 1 << WORK_STRUCT_PENDING_BIT,
+        WORK_STRUCT_LINKED      = 1 << WORK_STRUCT_LINKED_BIT,
 #ifdef CONFIG_DEBUG_OBJECTS_WORK
         WORK_STRUCT_STATIC      = 1 << WORK_STRUCT_STATIC_BIT,
 #else