[PATCH 6.8 006/715] workqueue: Move nr_active handling into helpers

Sasha Levin
2024-03-24T22:35:03Z

From: Tejun Heo <tj@kernel.org>

[ Upstream commit 1c270b79ce0b8290f146255ea9057243f6dd3c17 ]

__queue_work(), pwq_dec_nr_in_flight() and wq_adjust_max_active() were
open-coding nr_active handling, which is fine given that the operations are
trivial. However, the planned unbound nr_active update will make them more
complicated, so let's move them into helpers.

- pwq_tryinc_nr_active() is added. It increments nr_active if under
max_active limit and return a boolean indicating whether inc was
successful. Note that the function is structured to accommodate future
changes. __queue_work() is updated to use the new helper.

- pwq_activate_first_inactive() is updated to use pwq_tryinc_nr_active() and
thus no longer assumes that nr_active is under max_active and returns a
boolean to indicate whether a work item has been activated.

- wq_adjust_max_active() no longer tests directly whether a work item can be
activated. Instead, it's updated to use the return value of
pwq_activate_first_inactive() to tell whether a work item has been
activated.

- nr_active decrement and activating the first inactive work item is
factored into pwq_dec_nr_active().

v3: - WARN_ON_ONCE(!WORK_STRUCT_INACTIVE) added to __pwq_activate_work() as
now we're calling the function unconditionally from
pwq_activate_first_inactive().

v2: - wq->max_active now uses WRITE/READ_ONCE() as suggested by Lai.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>
Stable-dep-of: 5797b1c18919 ("workqueue: Implement system-wide nr_active enforcement for unbound workqueues")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/workqueue.c | 86 ++++++++++++++++++++++++++++++++++++----------
1 file changed, 67 insertions(+), 19 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 7e1b0238158ea..80733046ee012 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1464,11 +1464,14 @@ static bool pwq_is_empty(struct pool_workqueue *pwq)
static void __pwq_activate_work(struct pool_workqueue *pwq,
struct work_struct *work)
{
+ unsigned long *wdb = work_data_bits(work);
+
+ WARN_ON_ONCE(!(*wdb & WORK_STRUCT_INACTIVE));
trace_workqueue_activate_work(work);
if (list_empty(&pwq->pool->worklist))
pwq->pool->watchdog_ts = jiffies;
move_linked_works(work, &pwq->pool->worklist, NULL);
- __clear_bit(WORK_STRUCT_INACTIVE_BIT, work_data_bits(work));
+ __clear_bit(WORK_STRUCT_INACTIVE_BIT, wdb);
}

/**
@@ -1493,12 +1496,66 @@ static bool pwq_activate_work(struct pool_workqueue *pwq,
return true;
}

-static void pwq_activate_first_inactive(struct pool_workqueue *pwq)
+/**
+ * pwq_tryinc_nr_active - Try to increment nr_active for a pwq
+ * @pwq: pool_workqueue of interest
+ *
+ * Try to increment nr_active for @pwq. Returns %true if an nr_active count is
+ * successfully obtained. %false otherwise.
+ */
+static bool pwq_tryinc_nr_active(struct pool_workqueue *pwq)
+{
+ struct workqueue_struct *wq = pwq->wq;
+ struct worker_pool *pool = pwq->pool;
+ bool obtained;
+
+ lockdep_assert_held(&pool->lock);
+
+ obtained = pwq->nr_active < READ_ONCE(wq->max_active);
+
+ if (obtained)
+ pwq->nr_active++;
+ return obtained;
+}
+
+/**
+ * pwq_activate_first_inactive - Activate the first inactive work item on a pwq
+ * @pwq: pool_workqueue of interest
+ *
+ * Activate the first inactive work item of @pwq if available and allowed by
+ * max_active limit.
+ *
+ * Returns %true if an inactive work item has been activated. %false if no
+ * inactive work item is found or max_active limit is reached.
+ */
+static bool pwq_activate_first_inactive(struct pool_workqueue *pwq)
+{
+ struct work_struct *work =
+ list_first_entry_or_null(&pwq->inactive_works,
+ struct work_struct, entry);
+
+ if (work && pwq_tryinc_nr_active(pwq)) {
+ __pwq_activate_work(pwq, work);
+ return true;
+ } else {
+ return false;
+ }
+}
+
+/**
+ * pwq_dec_nr_active - Retire an active count
+ * @pwq: pool_workqueue of interest
+ *
+ * Decrement @pwq's nr_active and try to activate the first inactive work item.
+ */
+static void pwq_dec_nr_active(struct pool_workqueue *pwq)
{
- struct work_struct *work = list_first_entry(&pwq->inactive_works,
- struct work_struct, entry);
+ struct worker_pool *pool = pwq->pool;

- pwq_activate_work(pwq, work);
+ lockdep_assert_held(&pool->lock);
+
+ pwq->nr_active--;
+ pwq_activate_first_inactive(pwq);
}

/**
@@ -1516,14 +1573,8 @@ static void pwq_dec_nr_in_flight(struct pool_workqueue *pwq, unsigned long work_
{
int color = get_work_color(work_data);

- if (!(work_data & WORK_STRUCT_INACTIVE)) {
- pwq->nr_active--;
- if (!list_empty(&pwq->inactive_works)) {
- /* one down, submit an inactive one */
- if (pwq->nr_active < READ_ONCE(pwq->wq->max_active))
- pwq_activate_first_inactive(pwq);
- }
- }
+ if (!(work_data & WORK_STRUCT_INACTIVE))
+ pwq_dec_nr_active(pwq);

pwq->nr_in_flight[color]--;

@@ -1825,13 +1876,11 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
* @work must also queue behind existing inactive work items to maintain
* ordering when max_active changes. See wq_adjust_max_active().
*/
- if (list_empty(&pwq->inactive_works) &&
- pwq->nr_active < READ_ONCE(pwq->wq->max_active)) {
+ if (list_empty(&pwq->inactive_works) && pwq_tryinc_nr_active(pwq)) {
if (list_empty(&pool->worklist))
pool->watchdog_ts = jiffies;

trace_workqueue_activate_work(work);
- pwq->nr_active++;
insert_work(pwq, work, &pool->worklist, work_flags);
kick_pool(pool);
} else {
@@ -4680,9 +4729,8 @@ static void wq_adjust_max_active(struct workqueue_struct *wq)
/* this function can be called during early boot w/ irq disabled */
raw_spin_lock_irqsave(&pwq->pool->lock, flags);

- while (!list_empty(&pwq->inactive_works) &&
- pwq->nr_active < wq->max_active)
- pwq_activate_first_inactive(pwq);
+ while (pwq_activate_first_inactive(pwq))
+ ;

kick_pool(pwq->pool);

--
2.43.0