workqueue: Avoid nr_active manipulation in grabbing inactive items

Current try_to_grab_pending() activates the inactive item and
subsequently treats it as though it were a standard activated item.

This approach prevents duplicating handling logic for both active and
inactive items, yet the premature activation of an inactive item
triggers trace_workqueue_activate_work(), yielding an unintended user
space visible side effect.

And the unnecessary increment of the nr_active, which is not a simple
counter now, followed by a counteracted decrement, is inefficient and
complicates the code.

Just remove the nr_active manipulation code in grabbing inactive items.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index b06c88814dde8d37e17c061070daa3c48f9f8208..23e424bda7c2f6748e8c6633d7abbb0b955c9bb0 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1683,33 +1683,6 @@ static void __pwq_activate_work(struct pool_workqueue *pwq,
        __clear_bit(WORK_STRUCT_INACTIVE_BIT, wdb);
 }
 
-/**
- * pwq_activate_work - Activate a work item if inactive
- * @pwq: pool_workqueue @work belongs to
- * @work: work item to activate
- *
- * Returns %true if activated. %false if already active.
- */
-static bool pwq_activate_work(struct pool_workqueue *pwq,
-                             struct work_struct *work)
-{
-       struct worker_pool *pool = pwq->pool;
-       struct wq_node_nr_active *nna;
-
-       lockdep_assert_held(&pool->lock);
-
-       if (!(*work_data_bits(work) & WORK_STRUCT_INACTIVE))
-               return false;
-
-       nna = wq_node_nr_active(pwq->wq, pool->node);
-       if (nna)
-               atomic_inc(&nna->nr);
-
-       pwq->nr_active++;
-       __pwq_activate_work(pwq, work);
-       return true;
-}
-
 static bool tryinc_node_nr_active(struct wq_node_nr_active *nna)
 {
        int max = READ_ONCE(nna->max);
@@ -2116,7 +2089,7 @@ static int try_to_grab_pending(struct work_struct *work, u32 cflags,
         */
        pwq = get_work_pwq(work);
        if (pwq && pwq->pool == pool) {
-               unsigned long work_data;
+               unsigned long work_data = *work_data_bits(work);
 
                debug_work_deactivate(work);
 
@@ -2125,13 +2098,17 @@ static int try_to_grab_pending(struct work_struct *work, u32 cflags,
                 * pwq->inactive_works since a queued barrier can't be
                 * canceled (see the comments in insert_wq_barrier()).
                 *
-                * An inactive work item cannot be grabbed directly because
+                * An inactive work item cannot be deleted directly because
                 * it might have linked barrier work items which, if left
                 * on the inactive_works list, will confuse pwq->nr_active
-                * management later on and cause stall.  Make sure the work
-                * item is activated before grabbing.
+                * management later on and cause stall.  Move the linked
+                * barrier work items to the worklist when deleting the grabbed
+                * item. Also keep WORK_STRUCT_INACTIVE in work_data, so that
+                * it doesn't participate in nr_active management in later
+                * pwq_dec_nr_in_flight().
                 */
-               pwq_activate_work(pwq, work);
+               if (work_data & WORK_STRUCT_INACTIVE)
+                       move_linked_works(work, &pwq->pool->worklist, NULL);
 
                list_del_init(&work->entry);
 
@@ -2139,7 +2116,6 @@ static int try_to_grab_pending(struct work_struct *work, u32 cflags,
                 * work->data points to pwq iff queued. Let's point to pool. As
                 * this destroys work->data needed by the next step, stash it.
                 */
-               work_data = *work_data_bits(work);
                set_work_pool_and_keep_pending(work, pool->id,
                                               pool_offq_flags(pool));