linux-kernel - [PATCH-wq v2 5/5] workqueue: Bind unbound workqueue rescuer to wq_unbound

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Date: Sat,  3 Feb 2024 10:43:34 -0500
From: Waiman Long <longman@...hat.com>
To: Tejun Heo <tj@...nel.org>,
	Lai Jiangshan <jiangshanlai@...il.com>
Cc: linux-kernel@...r.kernel.org,
	Juri Lelli <juri.lelli@...hat.com>,
	Cestmir Kalina <ckalina@...hat.com>,
	Alex Gladkov <agladkov@...hat.com>,
	Phil Auld <pauld@...hat.com>,
	Costa Shulyupin <cshulyup@...hat.com>,
	Waiman Long <longman@...hat.com>
Subject: [PATCH-wq v2 5/5] workqueue: Bind unbound workqueue rescuer to wq_unbound_cpumask

Commit 85f0ab43f9de ("kernel/workqueue: Bind rescuer to unbound
cpumask for WQ_UNBOUND") modified init_rescuer() to bind rescuer of
an unbound workqueue to the cpumask in wq->unbound_attrs. However
unbound_attrs->cpumask's of all workqueues are initialized to
cpu_possible_mask and will only be changed if it has the WQ_SYSFS flag
to expose a cpumask sysfs file to be written by users. So this patch
doesn't achieve what it is intended to do.

If an unbound workqueue is created after wq_unbound_cpumask is modified
and there is no more unbound cpumask update after that, the unbound
rescuer will be bound to all CPUs unless the workqueue is created
with the WQ_SYSFS flag and an user explicitly modified its cpumask
sysfs file.  Fix this problem by binding directly to wq_unbound_cpumask
in init_rescuer().

Fixes: 85f0ab43f9de ("kernel/workqueue: Bind rescuer to unbound cpumask for WQ_UNBOUND")
Signed-off-by: Waiman Long <longman@...hat.com>
---
 kernel/workqueue.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 172f7299aa71..1e022899c13c 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -5149,7 +5149,7 @@ static int init_rescuer(struct workqueue_struct *wq)

 	wq->rescuer = rescuer;
 	if (wq->flags & WQ_UNBOUND)
-		kthread_bind_mask(rescuer->task, wq->unbound_attrs->cpumask);
+		kthread_bind_mask(rescuer->task, wq_unbound_cpumask);
 	else
 		kthread_bind_mask(rescuer->task, cpu_possible_mask);
 	wake_up_process(rescuer->task);
-- 
2.39.3