linux-kernel - [PATCH -tip V3 7/8] workqueue: reorganize workqueue_offline_cpu() unbind

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Message-Id: <20201226025117.2770-8-jiangshanlai@gmail.com>
Date:   Sat, 26 Dec 2020 10:51:15 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Valentin Schneider <valentin.schneider@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Qian Cai <cai@...hat.com>,
        Vincent Donnefort <vincent.donnefort@....com>,
        Dexuan Cui <decui@...rosoft.com>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: [PATCH -tip V3 7/8] workqueue: reorganize workqueue_offline_cpu() unbind_workers()

From: Lai Jiangshan <laijs@...ux.alibaba.com>

Just move around the code, no functionality changed.
Only wq_pool_attach_mutex protected region becomes a little larger.

It prepares for later patch protecting wq_online_cpumask
in wq_pool_attach_mutex.

Acked-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 kernel/workqueue.c | 90 +++++++++++++++++++++++-----------------------
 1 file changed, 45 insertions(+), 45 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 94545e6feda5..dd32398edf55 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4896,61 +4896,57 @@ void wq_worker_comm(char *buf, size_t size, struct task_struct *task)
  * cpu comes back online.
  */
 
-static void unbind_workers(int cpu)
+static void unbind_workers(struct worker_pool *pool)
 {
-	struct worker_pool *pool;
 	struct worker *worker;
 
-	for_each_cpu_worker_pool(pool, cpu) {
-		mutex_lock(&wq_pool_attach_mutex);
-		raw_spin_lock_irq(&pool->lock);
+	lockdep_assert_held(&wq_pool_attach_mutex);
 
-		/*
-		 * We've blocked all attach/detach operations. Make all workers
-		 * unbound and set DISASSOCIATED.  Before this, all workers
-		 * except for the ones which are still executing works from
-		 * before the last CPU down must be on the cpu.  After
-		 * this, they may become diasporas.
-		 */
-		for_each_pool_worker(worker, pool)
-			worker->flags |= WORKER_UNBOUND;
+	raw_spin_lock_irq(&pool->lock);
 
-		pool->flags |= POOL_DISASSOCIATED;
+	/*
+	 * We've blocked all attach/detach operations. Make all workers
+	 * unbound and set DISASSOCIATED.  Before this, all workers
+	 * except for the ones which are still executing works from
+	 * before the last CPU down must be on the cpu.  After
+	 * this, they may become diasporas.
+	 */
+	for_each_pool_worker(worker, pool)
+		worker->flags |= WORKER_UNBOUND;
 
-		raw_spin_unlock_irq(&pool->lock);
+	pool->flags |= POOL_DISASSOCIATED;
 
-		for_each_pool_worker(worker, pool)
-			WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);
+	raw_spin_unlock_irq(&pool->lock);
 
-		mutex_unlock(&wq_pool_attach_mutex);
+	for_each_pool_worker(worker, pool)
+		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);
 
-		/*
-		 * Call schedule() so that we cross rq->lock and thus can
-		 * guarantee sched callbacks see the %WORKER_UNBOUND flag.
-		 * This is necessary as scheduler callbacks may be invoked
-		 * from other cpus.
-		 */
-		schedule();
+	/*
+	 * Call schedule() so that we cross rq->lock and thus can
+	 * guarantee sched callbacks see the %WORKER_UNBOUND flag.
+	 * This is necessary as scheduler callbacks may be invoked
+	 * from other cpus.
+	 */
+	schedule();
 
-		/*
-		 * Sched callbacks are disabled now.  Zap nr_running.
-		 * After this, nr_running stays zero and need_more_worker()
-		 * and keep_working() are always true as long as the
-		 * worklist is not empty.  This pool now behaves as an
-		 * unbound (in terms of concurrency management) pool which
-		 * are served by workers tied to the pool.
-		 */
-		atomic_set(&pool->nr_running, 0);
+	/*
+	 * Sched callbacks are disabled now.  Zap nr_running.
+	 * After this, nr_running stays zero and need_more_worker()
+	 * and keep_working() are always true as long as the
+	 * worklist is not empty.  This pool now behaves as an
+	 * unbound (in terms of concurrency management) pool which
+	 * are served by workers tied to the pool.
+	 */
+	atomic_set(&pool->nr_running, 0);
 
-		/*
-		 * With concurrency management just turned off, a busy
-		 * worker blocking could lead to lengthy stalls.  Kick off
-		 * unbound chain execution of currently pending work items.
-		 */
-		raw_spin_lock_irq(&pool->lock);
-		wake_up_worker(pool);
-		raw_spin_unlock_irq(&pool->lock);
-	}
+	/*
+	 * With concurrency management just turned off, a busy
+	 * worker blocking could lead to lengthy stalls.  Kick off
+	 * unbound chain execution of currently pending work items.
+	 */
+	raw_spin_lock_irq(&pool->lock);
+	wake_up_worker(pool);
+	raw_spin_unlock_irq(&pool->lock);
 }
 
 /**
@@ -5122,7 +5118,11 @@ int workqueue_offline_cpu(unsigned int cpu)
 	if (WARN_ON(cpu != smp_processor_id()))
 		return -1;
 
-	unbind_workers(cpu);
+	for_each_cpu_worker_pool(pool, cpu) {
+		mutex_lock(&wq_pool_attach_mutex);
+		unbind_workers(pool);
+		mutex_unlock(&wq_pool_attach_mutex);
+	}
 
 	mutex_lock(&wq_pool_mutex);
 	cpumask_clear_cpu(cpu, wq_online_cpumask);
-- 
2.19.1.6.gb485710b