linux-kernel - [PATCH -v3 2/9] workqueue: Use cpu_possible_mask instead of cpu_active

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Date:   Thu, 21 Jan 2021 11:17:04 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org, tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, jiangshanlai@...il.com,
        valentin.schneider@....com, cai@...hat.com,
        vincent.donnefort@....com, decui@...rosoft.com, paulmck@...nel.org,
        vincent.guittot@...aro.org, rostedt@...dmis.org, tj@...nel.org,
        peterz@...radead.org, Lai Jiangshan <laijs@...ux.alibaba.com>
Subject: [PATCH -v3 2/9] workqueue: Use cpu_possible_mask instead of cpu_active_mask to break affinity

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

The scheduler won't break affinity for us any more, and we should
"emulate" the same behavior when the scheduler breaks affinity for
us.  The behavior is "changing the cpumask to cpu_possible_mask".

And there might be some other CPUs online later while the worker is
still running with the pending work items.  The worker should be allowed
to use the later online CPUs as before and process the work items ASAP.
If we use cpu_active_mask here, we can't achieve this goal but
using cpu_possible_mask can.

Fixes: 06249738a41a ("workqueue: Manually break affinity on hotplug")
Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Tejun Heo <tj@...nel.org>
Tested-by: Paul E. McKenney <paulmck@...nel.org>
Link: https://lkml.kernel.org/r/20210111152638.2417-4-jiangshanlai@gmail.com
---
 kernel/workqueue.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4920,7 +4920,7 @@ static void unbind_workers(int cpu)
 		raw_spin_unlock_irq(&pool->lock);
 
 		for_each_pool_worker(worker, pool)
-			WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_active_mask) < 0);
+			WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);
 
 		mutex_unlock(&wq_pool_attach_mutex);