linux-kernel - [PATCH 03/10] workqueue: Manually break affinity on pool detachment

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Date:   Mon, 14 Dec 2020 23:54:50 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>, Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: [PATCH 03/10] workqueue: Manually break affinity on pool detachment

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

Don't rely on the scheduler to force break affinity for us -- it will
stop doing that for per-cpu-kthreads.

Fixes: 06249738a41a ("workqueue: Manually break affinity on hotplug")
Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 kernel/workqueue.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1f5b8385c0cf..1f6cb83e0bc5 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1885,6 +1885,16 @@ static void worker_detach_from_pool(struct worker *worker)
 
 	if (list_empty(&pool->workers))
 		detach_completion = pool->detach_completion;
+
+	/*
+	 * The cpus of pool->attrs->cpumask might all go offline after
+	 * detachment, and the scheduler may not force break affinity
+	 * for us, so we 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 it.
+	 */
+	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