[PATCH 6/6] workqueue: Record real per-workqueue cpumask

[Frederic Weisbecker <fweisbec@gmail.com>]

The real cpumask set by the user on WQ_SYSFS workqueues fails to be
recorded as is: What is actually recorded as per workqueue attribute
is the per workqueue cpumask intersected with the global unbounds cpumask.

Eventually when the user overwrites a WQ_SYSFS cpumask and later read
this attibute, the value returned is not the last one written.

The other bad side effect is that widening the global unbounds cpumask
doesn't actually widen the unbound workqueues affinity because their
own cpumask has been schrinked.

In order to fix this, lets record the real per workqueue cpumask on the
workqueue struct. We restore this value when attributes are re-evaluated
later.

FIXME: Maybe I should rather invert that. Have the user set workqueue
cpumask on attributes and the effective one on the workqueue struct instead.
We'll just need some tweaking in order to make the attributes of lower layers
(pools, worker pools, worker, ...) to inherit the effective cpumask and not
the user one.

Cc: Christoph Lameter <cl@linux.com>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Mike Galbraith <bitbucket@online.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 kernel/workqueue.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 5978cee..504cf0a 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -248,6 +248,7 @@ struct workqueue_struct {
 	int			saved_max_active; /* WQ: saved pwq max_active */
 
 	struct workqueue_attrs	*unbound_attrs;	/* WQ: only for unbound wqs */
+	cpumask_var_t		saved_cpumask;	/* WQ: only for unbound wqs */
 	struct pool_workqueue	*dfl_pwq;	/* WQ: only for unbound wqs */
 
 #ifdef CONFIG_SYSFS
@@ -3694,6 +3695,7 @@ static int apply_workqueue_attrs_locked(struct workqueue_struct *wq,
 	mutex_lock(&wq->mutex);
 
 	copy_workqueue_attrs(wq->unbound_attrs, new_attrs);
+	cpumask_copy(wq->saved_cpumask, attrs->cpumask);
 
 	/* save the previous pwq and install the new one */
 	for_each_node(node)
@@ -4326,6 +4328,11 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
 		wq->unbound_attrs = alloc_workqueue_attrs(GFP_KERNEL);
 		if (!wq->unbound_attrs)
 			goto err_free_wq;
+
+		if (!alloc_cpumask_var(&wq->saved_cpumask, GFP_KERNEL))
+			goto err_free_wq;
+
+		cpumask_copy(wq->saved_cpumask, cpu_possible_mask);
 	}
 
 	va_start(args, lock_name);
@@ -4397,6 +4404,7 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
 	return wq;
 
 err_free_wq:
+	free_cpumask_var(wq->saved_cpumask);
 	free_workqueue_attrs(wq->unbound_attrs);
 	kfree(wq);
 	return NULL;
-- 
1.8.3.1