linux-kernel - [PATCH -tip V3 2/8] workqueue: Manually break affinity on pool detachment

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Date:   Sat, 26 Dec 2020 10:51:10 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Valentin Schneider <valentin.schneider@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Qian Cai <cai@...hat.com>,
        Vincent Donnefort <vincent.donnefort@....com>,
        Dexuan Cui <decui@...rosoft.com>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: [PATCH -tip V3 2/8] workqueue: Manually break affinity on pool detachment

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

The pool->attrs->cpumask might be a single CPU and it may go
down after detachment, and the scheduler won't force to break
affinity for us since it is a per-cpu-ktrhead.  So we have to
do it on our own and unbind this worker which can't be unbound
by workqueue_offline_cpu() since it doesn't belong to any pool
after detachment.  Do it unconditionally for there is no harm
to break affinity for non-per-cpu-ktrhead and we don't need to
rely on the scheduler's policy on when to break affinity.

Fixes: 06249738a41a ("workqueue: Manually break affinity on hotplug")
Acked-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 kernel/workqueue.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index f2b8f3d458d1..ccbceacaea1b 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1885,6 +1885,19 @@ static void worker_detach_from_pool(struct worker *worker)
 
 	if (list_empty(&pool->workers))
 		detach_completion = pool->detach_completion;
+
+	/*
+	 * The pool->attrs->cpumask might be a single CPU and it may go
+	 * down after detachment, and the scheduler won't force to break
+	 * affinity for us since it is a per-cpu-ktrhead.  So we have to
+	 * do it on our own and unbind this worker which can't be unbound
+	 * by workqueue_offline_cpu() since it doesn't belong to any pool
+	 * after detachment.  Do it unconditionally for there is no harm
+	 * to break affinity for non-per-cpu-ktrhead and we don't need to
+	 * rely on the scheduler's policy on when to break affinity.
+	 */
+	set_cpus_allowed_ptr(worker->task, cpu_possible_mask);
+
 	mutex_unlock(&wq_pool_attach_mutex);
 
 	/* clear leftover flags without pool->lock after it is detached */
-- 
2.19.1.6.gb485710b