From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
v4.14.292-rt138-rc2 stable review patch.
If anyone has any objections, please let me know.
-----------
This reverts the PREEMPT_RT related changes to workqueue. It reverts the
extra locking needed to protect the worker which will soon become
obsolete.
The sched/core.c changes, which were introduced in the original commit,
must remain as the following code will rely on it.
This is a preparation to pull in the PREEMPT_RT related changes which
were merged upstream.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Message-Id: <20220819092446.980320-5-bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@xxxxxxxxxx>
---
kernel/workqueue.c | 60 ++++++++++------------------------------------
1 file changed, 13 insertions(+), 47 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 856a2089f8632..cfca5027c3a21 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -124,11 +124,6 @@ enum {
* cpu or grabbing pool->lock is enough for read access. If
* POOL_DISASSOCIATED is set, it's identical to L.
*
- * On RT we need the extra protection via rt_lock_idle_list() for
- * the list manipulations against read access from
- * wq_worker_sleeping(). All other places are nicely serialized via
- * pool->lock.
- *
* A: pool->attach_mutex protected.
*
* PL: wq_pool_mutex protected.
@@ -434,31 +429,6 @@ static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
if (({ assert_rcu_or_wq_mutex(wq); false; })) { } \
else
-#ifdef CONFIG_PREEMPT_RT_BASE
-static inline void rt_lock_idle_list(struct worker_pool *pool)
-{
- preempt_disable();
-}
-static inline void rt_unlock_idle_list(struct worker_pool *pool)
-{
- preempt_enable();
-}
-static inline void sched_lock_idle_list(struct worker_pool *pool) { }
-static inline void sched_unlock_idle_list(struct worker_pool *pool) { }
-#else
-static inline void rt_lock_idle_list(struct worker_pool *pool) { }
-static inline void rt_unlock_idle_list(struct worker_pool *pool) { }
-static inline void sched_lock_idle_list(struct worker_pool *pool)
-{
- spin_lock_irq(&pool->lock);
-}
-static inline void sched_unlock_idle_list(struct worker_pool *pool)
-{
- spin_unlock_irq(&pool->lock);
-}
-#endif
-
-
#ifdef CONFIG_DEBUG_OBJECTS_WORK
static struct debug_obj_descr work_debug_descr;
@@ -865,16 +835,10 @@ static struct worker *first_idle_worker(struct worker_pool *pool)
*/
static void wake_up_worker(struct worker_pool *pool)
{
- struct worker *worker;
-
- rt_lock_idle_list(pool);
-
- worker = first_idle_worker(pool);
+ struct worker *worker = first_idle_worker(pool);
if (likely(worker))
wake_up_process(worker->task);
-
- rt_unlock_idle_list(pool);
}
/**
@@ -903,7 +867,7 @@ void wq_worker_running(struct task_struct *task)
*/
void wq_worker_sleeping(struct task_struct *task)
{
- struct worker *worker = kthread_data(task);
+ struct worker *next, *worker = kthread_data(task);
struct worker_pool *pool;
/*
@@ -920,18 +884,26 @@ void wq_worker_sleeping(struct task_struct *task)
return;
worker->sleeping = 1;
+ spin_lock_irq(&pool->lock);
/*
* The counterpart of the following dec_and_test, implied mb,
* worklist not empty test sequence is in insert_work().
* Please read comment there.
+ *
+ * NOT_RUNNING is clear. This means that we're bound to and
+ * running on the local cpu w/ rq lock held and preemption
+ * disabled, which in turn means that none else could be
+ * manipulating idle_list, so dereferencing idle_list without pool
+ * lock is safe.
*/
if (atomic_dec_and_test(&pool->nr_running) &&
!list_empty(&pool->worklist)) {
- sched_lock_idle_list(pool);
- wake_up_worker(pool);
- sched_unlock_idle_list(pool);
+ next = first_idle_worker(pool);
+ if (next)
+ wake_up_process(next->task);
}
+ spin_unlock_irq(&pool->lock);
}
/**
@@ -1662,9 +1634,7 @@ static void worker_enter_idle(struct worker *worker)
worker->last_active = jiffies;
/* idle_list is LIFO */
- rt_lock_idle_list(pool);
list_add(&worker->entry, &pool->idle_list);
- rt_unlock_idle_list(pool);
if (too_many_workers(pool) && !timer_pending(&pool->idle_timer))
mod_timer(&pool->idle_timer, jiffies + IDLE_WORKER_TIMEOUT);
@@ -1697,9 +1667,7 @@ static void worker_leave_idle(struct worker *worker)
return;
worker_clr_flags(worker, WORKER_IDLE);
pool->nr_idle--;
- rt_lock_idle_list(pool);
list_del_init(&worker->entry);
- rt_unlock_idle_list(pool);
}
static struct worker *alloc_worker(int node)
@@ -1865,9 +1833,7 @@ static void destroy_worker(struct worker *worker)
pool->nr_workers--;
pool->nr_idle--;
- rt_lock_idle_list(pool);
list_del_init(&worker->entry);
- rt_unlock_idle_list(pool);
worker->flags |= WORKER_DIE;
wake_up_process(worker->task);
}
--
2.37.3
