linux-kernel - [PATCH-wq v3 3/4] kernel/workqueue: Let rescuers follow unbound wq cpumask changes

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Date: Mon,  5 Feb 2024 14:46:01 -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 v3 3/4] kernel/workqueue: Let rescuers follow unbound wq cpumask changes

From: Juri Lelli <juri.lelli@...hat.com>

When workqueue cpumask changes are committed the associated rescuer (if
one exists) affinity is not touched and this might be a problem down the
line for isolated setups.

Make sure rescuers affinity is updated every time a workqueue cpumask
changes, so that rescuers can't break isolation.

 [longman: set_cpus_allowed_ptr() will block until the designated task
  is enqueued on an allowed CPU, no wake_up_process() needed. Also use
  the unbound_effective_cpumask() helper as suggested by Tejun.]

Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
Signed-off-by: Waiman Long <longman@...hat.com>
Tested-by: Juri Lelli <juri.lelli@...hat.com>
---
 kernel/workqueue.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index f453f339f74a..bbd4269d2729 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -5049,6 +5049,11 @@ static void apply_wqattrs_commit(struct apply_wqattrs_ctx *ctx)
 	/* update node_nr_active->max */
 	wq_update_node_max_active(ctx->wq, -1);
 
+	/* rescuer needs to respect wq cpumask changes */
+	if (ctx->wq->rescuer)
+		set_cpus_allowed_ptr(ctx->wq->rescuer->task,
+				     unbound_effective_cpumask(ctx->wq));
+
 	mutex_unlock(&ctx->wq->mutex);
 }
 
-- 
2.39.3