Currently if a user enqueue a work item using schedule_delayed_work() the
used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use
WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to
schedule_work() that is using system_wq and queue_work(), that makes use
again of WORK_CPU_UNBOUND.

This lack of consistentcy cannot be addressed without refactoring the API.

system_unbound_wq should be the default workqueue so as not to enforce
locality constraints for random work whenever it's not required.

Adding system_dfl_wq to encourage its use when unbound work should be used.

queue_work() / queue_delayed_work() / mod_delayed_work() will now use the
new unbound wq: whether the user still use the old wq a warn will be
printed along with a wq redirect to the new one.

The old system_unbound_wq will be kept for a few release cycles.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
---
 include/linux/workqueue.h | 4 ++--
 kernel/workqueue.c        | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index f19072605faa..0e14d78fb970 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -779,8 +779,8 @@ extern void __warn_flushing_systemwide_wq(void)
 	     _wq == system_highpri_wq) ||				\
 	    (__builtin_constant_p(_wq == system_long_wq) &&		\
 	     _wq == system_long_wq) ||					\
-	    (__builtin_constant_p(_wq == system_unbound_wq) &&		\
-	     _wq == system_unbound_wq) ||				\
+	    (__builtin_constant_p(_wq == system_dfl_wq) &&		\
+	     _wq == system_dfl_wq) ||				\
 	    (__builtin_constant_p(_wq == system_freezable_wq) &&	\
 	     _wq == system_freezable_wq) ||				\
 	    (__builtin_constant_p(_wq == system_power_efficient_wq) &&	\
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 62f020050de1..687285701655 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2936,7 +2936,7 @@ static void idle_worker_timeout(struct timer_list *t)
 	raw_spin_unlock_irq(&pool->lock);
 
 	if (do_cull)
-		queue_work(system_unbound_wq, &pool->idle_cull_work);
+		queue_work(system_dfl_wq, &pool->idle_cull_work);
 }
 
 /**
-- 
2.51.0