linux-kernel - [RFC PATCH 3/4] kernel/workqueue: Distinguish between general unbound and WQ

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Date: Tue, 16 Jan 2024 17:19:28 +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 3/4] kernel/workqueue: Distinguish between general unbound and WQ_SYSFS cpumask changes

Both general unbound cpumask and per-wq (WQ_SYSFS) cpumask changes end
up calling apply_wqattrs_prepare for preparing for the change, but this
doesn't work well for general unbound cpumask changes as current
implementation won't be looking at the new unbound_cpumask.

Fix the prepare phase for general unbound cpumask changes by checking
which type of attributes (general vs. WQ_SYSFS) are actually changing.

Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
---
 kernel/workqueue.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 3a1d5a67bd66a..2ef6573909070 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4359,7 +4359,17 @@ apply_wqattrs_prepare(struct workqueue_struct *wq,
 	 * it even if we don't use it immediately.
 	 */
 	copy_workqueue_attrs(new_attrs, attrs);
-	wqattrs_actualize_cpumask(new_attrs, unbound_cpumask);
+
+	/*
+	 * Is the user changing the general unbound_cpumask or is this a
+	 * WQ_SYSFS cpumask change?
+	 */
+	if (attrs == wq->unbound_attrs)
+		cpumask_copy(new_attrs->cpumask, unbound_cpumask);
+	else
+		wqattrs_actualize_cpumask(new_attrs, unbound_cpumask);
+
+	cpumask_and(new_attrs->cpumask, new_attrs->cpumask, cpu_possible_mask);
 	cpumask_copy(new_attrs->__pod_cpumask, new_attrs->cpumask);
 	ctx->dfl_pwq = alloc_unbound_pwq(wq, new_attrs);
 	if (!ctx->dfl_pwq)
@@ -4377,12 +4387,7 @@ apply_wqattrs_prepare(struct workqueue_struct *wq,
 		}
 	}
 
-	/* save the user configured attrs and sanitize it. */
-	copy_workqueue_attrs(new_attrs, attrs);
-	cpumask_and(new_attrs->cpumask, new_attrs->cpumask, cpu_possible_mask);
-	cpumask_copy(new_attrs->__pod_cpumask, new_attrs->cpumask);
 	ctx->attrs = new_attrs;
-
 	ctx->wq = wq;
 	return ctx;
 
-- 
2.43.0