[RFC PATCH v1 1/6] workqueue: Add set_workqueue_cpumask() helper function

[Ammar Faizi <ammarfaizi2@gnuweeb.org>]

Allow users to specify a CPU set for the workqueue. The first use case
of this helper function is to set the CPU affinity of Btrfs workqueues.

Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---
 include/linux/workqueue.h |  3 +++
 kernel/workqueue.c        | 19 +++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index ac551b8ee7d9f2f4..e3bd6f47e74ecd66 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -710,6 +710,9 @@ int workqueue_online_cpu(unsigned int cpu);
 int workqueue_offline_cpu(unsigned int cpu);
 #endif
 
+int set_workqueue_cpumask(struct workqueue_struct *wq,
+			  const cpumask_var_t mask);
+
 void __init workqueue_init_early(void);
 void __init workqueue_init(void);
 
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index b8b541caed4854a4..adc1478fafb1811c 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4398,6 +4398,25 @@ static int init_rescuer(struct workqueue_struct *wq)
 	return 0;
 }
 
+int set_workqueue_cpumask(struct workqueue_struct *wq, const cpumask_var_t mask)
+{
+	struct workqueue_attrs *tmp_attrs;
+	int ret;
+
+	tmp_attrs = alloc_workqueue_attrs();
+	if (!tmp_attrs)
+		return -ENOMEM;
+
+	apply_wqattrs_lock();
+	copy_workqueue_attrs(tmp_attrs, wq->unbound_attrs);
+	cpumask_copy(tmp_attrs->cpumask, mask);
+	ret = apply_workqueue_attrs_locked(wq, tmp_attrs);
+	apply_wqattrs_unlock();
+	free_workqueue_attrs(tmp_attrs);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(set_workqueue_cpumask);
+
 __printf(1, 4)
 struct workqueue_struct *alloc_workqueue(const char *fmt,
 					 unsigned int flags,
-- 
Ammar Faizi