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

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Date: Tue, 16 Jan 2024 17:19:29 +0100
From: Juri Lelli <juri.lelli@...hat.com>
To: Tejun Heo <tj@...nel.org>
Cc: Lai Jiangshan <jiangshanlai@...il.com>,
	Aaron Tomlin <atomlin@...mlin.com>,
	Valentin Schneider <vschneid@...hat.com>,
	Waiman Long <longman@...hat.com>,
	Juri Lelli <juri.lelli@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH 4/4] kernel/workqueue: Let rescuers follow unbound wq cpumask changes

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.

Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
---
 kernel/workqueue.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 2ef6573909070..df7f2f2bfd0c8 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4416,6 +4416,12 @@ static void apply_wqattrs_commit(struct apply_wqattrs_ctx *ctx)
 	link_pwq(ctx->dfl_pwq);
 	swap(ctx->wq->dfl_pwq, ctx->dfl_pwq);
 
+	/* rescuer needs to respect wq cpumask changes */
+	if (ctx->wq->rescuer) {
+		set_cpus_allowed_ptr(ctx->wq->rescuer->task, ctx->attrs->cpumask);
+		wake_up_process(ctx->wq->rescuer->task);
+	}
+
 	mutex_unlock(&ctx->wq->mutex);
 }
 
-- 
2.43.0