linux-kernel - [RFC PATCH 4/8] workqueue: Set/Clear PF_WQ

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Date:   Thu,  4 Aug 2022 16:41:31 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <jiangshan.ljs@...group.com>,
        Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: [RFC PATCH 4/8] workqueue: Set/Clear PF_WQ_WORKER while attaching/detaching

From: Lai Jiangshan <jiangshan.ljs@...group.com>

PF_WQ_WORKER is only needed when the worker is attached.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
---
 kernel/workqueue.c | 32 ++++++++++++--------------------
 1 file changed, 12 insertions(+), 20 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 82937c0fb21f..7fc4c2fa21d6 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1861,6 +1861,8 @@ static struct worker *alloc_worker(int node)
 static void worker_attach_to_pool(struct worker *worker,
 				   struct worker_pool *pool)
 {
+	WARN_ON_ONCE(worker->task != current);
+
 	mutex_lock(&wq_pool_attach_mutex);
 
 	/*
@@ -1882,6 +1884,9 @@ static void worker_attach_to_pool(struct worker *worker,
 	list_add_tail(&worker->node, &pool->workers);
 	worker->pool = pool;
 
+	/* tell the scheduler that this is a workqueue worker */
+	current->flags |= PF_WQ_WORKER;
+
 	mutex_unlock(&wq_pool_attach_mutex);
 }
 
@@ -1898,8 +1903,11 @@ static void worker_detach_from_pool(struct worker *worker)
 	struct worker_pool *pool = worker->pool;
 	struct completion *detach_completion = NULL;
 
+	WARN_ON_ONCE(worker->task != current);
+
 	mutex_lock(&wq_pool_attach_mutex);
 
+	current->flags &= ~PF_WQ_WORKER;
 	kthread_set_per_cpu(worker->task, -1);
 	list_del(&worker->node);
 	worker->pool = NULL;
@@ -2352,16 +2360,6 @@ static void process_scheduled_works(struct worker *worker)
 	}
 }
 
-static void set_pf_worker(bool val)
-{
-	mutex_lock(&wq_pool_attach_mutex);
-	if (val)
-		current->flags |= PF_WQ_WORKER;
-	else
-		current->flags &= ~PF_WQ_WORKER;
-	mutex_unlock(&wq_pool_attach_mutex);
-}
-
 /**
  * worker_thread - the worker thread function
  * @__worker: self
@@ -2384,9 +2382,6 @@ static int worker_thread(void *__worker)
 	/* attach the worker to the pool */
 	worker_attach_to_pool(worker, pool);
 
-	/* tell the scheduler that this is a workqueue worker */
-	set_pf_worker(true);
-
 	raw_spin_lock_irq(&pool->lock);
 	worker->pool->nr_workers++;
 	worker_enter_idle(worker);
@@ -2397,7 +2392,6 @@ static int worker_thread(void *__worker)
 	if (unlikely(worker->flags & WORKER_DIE)) {
 		raw_spin_unlock_irq(&pool->lock);
 		WARN_ON_ONCE(!list_empty(&worker->entry));
-		set_pf_worker(false);
 
 		set_task_comm(worker->task, "kworker/dying");
 		ida_free(&pool->worker_ida, worker->id);
@@ -2498,11 +2492,6 @@ static int rescuer_thread(void *__rescuer)
 	current->flags |= PF_NO_SETAFFINITY;
 	set_user_nice(current, RESCUER_NICE_LEVEL);
 
-	/*
-	 * Mark rescuer as worker too.  As WORKER_PREP is never cleared, it
-	 * doesn't participate in concurrency management.
-	 */
-	set_pf_worker(true);
 repeat:
 	set_current_state(TASK_IDLE);
 
@@ -2531,6 +2520,10 @@ static int rescuer_thread(void *__rescuer)
 
 		raw_spin_unlock_irq(&wq_mayday_lock);
 
+		/*
+		 * Attach the rescuer.  As WORKER_PREP is never cleared, it
+		 * doesn't participate in concurrency management.
+		 */
 		worker_attach_to_pool(rescuer, pool);
 
 		raw_spin_lock_irq(&pool->lock);
@@ -2600,7 +2593,6 @@ static int rescuer_thread(void *__rescuer)
 
 	if (should_stop) {
 		__set_current_state(TASK_RUNNING);
-		set_pf_worker(false);
 		return 0;
 	}
 
-- 
2.19.1.6.gb485710b