workqueue: Move workqueue_set_unbound_cpumask() and its helpers inside CONFIG_SYSFS

Commit fe28f63 ("workqueue: Add workqueue_unbound_exclude_cpumask()
to exclude CPUs from wq_unbound_cpumask") makes
workqueue_set_unbound_cpumask() static as it is not used elsewhere in
the kernel. However, this triggers a kernel test robot warning about
'workqueue_set_unbound_cpumask' defined but not used when CONFIG_SYS
isn't defined. It happens that workqueue_set_unbound_cpumask() is only
called when CONFIG_SYS is defined.

Move workqueue_set_unbound_cpumask() and its helpers inside the
CONFIG_SYSFS compilation block to avoid the warning. There is no
functional change.

Fixes: fe28f63 ("workqueue: Add workqueue_unbound_exclude_cpumask() to exclude CPUs from wq_unbound_cpumask")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202311130831.uh0AoCd1-lkp@intel.com/
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Author: Waiman-Long

kernel/workqueue.c

@@ -4417,19 +4417,6 @@ static void apply_wqattrs_commit(struct apply_wqattrs_ctx *ctx)
 	mutex_unlock(&ctx->wq->mutex);
 }
 
-static void apply_wqattrs_lock(void)
-{
-	/* CPUs should stay stable across pwq creations and installations */
-	cpus_read_lock();
-	mutex_lock(&wq_pool_mutex);
-}
-
-static void apply_wqattrs_unlock(void)
-{
-	mutex_unlock(&wq_pool_mutex);
-	cpus_read_unlock();
-}
-
 static int apply_workqueue_attrs_locked(struct workqueue_struct *wq,
 					const struct workqueue_attrs *attrs)
 {
@@ -5833,44 +5820,6 @@ static int workqueue_apply_unbound_cpumask(const cpumask_var_t unbound_cpumask)
 	return ret;
 }
 
-/**
- *  workqueue_set_unbound_cpumask - Set the low-level unbound cpumask
- *  @cpumask: the cpumask to set
- *
- *  The low-level workqueues cpumask is a global cpumask that limits
- *  the affinity of all unbound workqueues.  This function check the @cpumask
- *  and apply it to all unbound workqueues and updates all pwqs of them.
- *
- *  Return:	0	- Success
- *  		-EINVAL	- Invalid @cpumask
- *  		-ENOMEM	- Failed to allocate memory for attrs or pwqs.
- */
-static int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
-{
-	int ret = -EINVAL;
-
-	/*
-	 * Not excluding isolated cpus on purpose.
-	 * If the user wishes to include them, we allow that.
-	 */
-	cpumask_and(cpumask, cpumask, cpu_possible_mask);
-	if (!cpumask_empty(cpumask)) {
-		apply_wqattrs_lock();
-		cpumask_copy(wq_requested_unbound_cpumask, cpumask);
-		if (cpumask_equal(cpumask, wq_unbound_cpumask)) {
-			ret = 0;
-			goto out_unlock;
-		}
-
-		ret = workqueue_apply_unbound_cpumask(cpumask);
-
-out_unlock:
-		apply_wqattrs_unlock();
-	}
-
-	return ret;
-}
-
 /**
  * workqueue_unbound_exclude_cpumask - Exclude given CPUs from unbound cpumask
  * @exclude_cpumask: the cpumask to be excluded from wq_unbound_cpumask
@@ -6027,6 +5976,19 @@ static struct attribute *wq_sysfs_attrs[] = {
 };
 ATTRIBUTE_GROUPS(wq_sysfs);
 
+static void apply_wqattrs_lock(void)
+{
+	/* CPUs should stay stable across pwq creations and installations */
+	cpus_read_lock();
+	mutex_lock(&wq_pool_mutex);
+}
+
+static void apply_wqattrs_unlock(void)
+{
+	mutex_unlock(&wq_pool_mutex);
+	cpus_read_unlock();
+}
+
 static ssize_t wq_nice_show(struct device *dev, struct device_attribute *attr,
 			    char *buf)
 {
@@ -6203,6 +6165,44 @@ static struct bus_type wq_subsys = {
 	.dev_groups			= wq_sysfs_groups,
 };
 
+/**
+ *  workqueue_set_unbound_cpumask - Set the low-level unbound cpumask
+ *  @cpumask: the cpumask to set
+ *
+ *  The low-level workqueues cpumask is a global cpumask that limits
+ *  the affinity of all unbound workqueues.  This function check the @cpumask
+ *  and apply it to all unbound workqueues and updates all pwqs of them.
+ *
+ *  Return:	0	- Success
+ *		-EINVAL	- Invalid @cpumask
+ *		-ENOMEM	- Failed to allocate memory for attrs or pwqs.
+ */
+static int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
+{
+	int ret = -EINVAL;
+
+	/*
+	 * Not excluding isolated cpus on purpose.
+	 * If the user wishes to include them, we allow that.
+	 */
+	cpumask_and(cpumask, cpumask, cpu_possible_mask);
+	if (!cpumask_empty(cpumask)) {
+		apply_wqattrs_lock();
+		cpumask_copy(wq_requested_unbound_cpumask, cpumask);
+		if (cpumask_equal(cpumask, wq_unbound_cpumask)) {
+			ret = 0;
+			goto out_unlock;
+		}
+
+		ret = workqueue_apply_unbound_cpumask(cpumask);
+
+out_unlock:
+		apply_wqattrs_unlock();
+	}
+
+	return ret;
+}
+
 static ssize_t __wq_cpumask_show(struct device *dev,
 		struct device_attribute *attr, char *buf, cpumask_var_t mask)
 {