[PATCH -tip V4 2/8] workqueue: set pool->attr->cpumask to workers when cpu online

[Lai Jiangshan <jiangshanlai@gmail.com>]

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

The commit d945b5e9f0e("workqueue: Fix setting affinity of unbound worker
threads") fixed a problem of set_cpus_allowed_ptr() with online&!active
cpumasks (more than one CPUs) when restore_unbound_workers_cpumask() in
online callback.

But now the new online callback for unbound workqueue is called later
than sched_cpu_activate().  So the cpu is set in cpu_active_mask and
set_cpus_allowed_ptr() with pool->attrs->cpumask in the code won't
cause such warning any more.

The said commit also left comments outdated and causes confusing.
It is better to change the code back.

Cc: Hillf Danton <hdanton@sina.com>
Reported-by: Hillf Danton <hdanton@sina.com>
Acked-by: Tejun Heo <tj@kernel.org>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 kernel/workqueue.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index d7bdb7885e55..38628e2a622c 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -5039,11 +5039,15 @@ static void restore_unbound_workers_cpumask(struct worker_pool *pool, int cpu)
 	if (!cpumask_test_cpu(cpu, pool->attrs->cpumask))
 		return;
 
+	/* is @cpu the only online CPU? */
 	cpumask_and(&cpumask, pool->attrs->cpumask, cpu_online_mask);
+	if (cpumask_weight(&cpumask) != 1)
+		return;
 
 	/* as we're called from CPU_ONLINE, the following shouldn't fail */
 	for_each_pool_worker(worker, pool)
-		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, &cpumask) < 0);
+		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
+						  pool->attrs->cpumask) < 0);
 }
 
 int workqueue_prepare_cpu(unsigned int cpu)
-- 
2.19.1.6.gb485710b