[PATCH v4 2/2] doc: Update WQ_UNBOUND and WQ_BH documentation

[Marco Crivellari <marco.crivellari@suse.com>]

When WQ_PERCPU is not present the default behavior is now WQ_UNBOUND,
so update the documentation, reflecting this change.

WQ_BH workqueues are the exception to this rule: they are always
per-CPU and can't be unbound, so WQ_PERCPU is implicitly set for them
regardless of what the caller passes. Update the WQ_BH section
accordingly, as WQ_HIGHPRI is no longer the only additional flag
involved.

Link: https://lore.kernel.org/all/20250221112003.1dSuoGyc@linutronix.de/
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
---
 Documentation/core-api/workqueue.rst | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/Documentation/core-api/workqueue.rst b/Documentation/core-api/workqueue.rst
index bb770f556568..76b70e7f4e3f 100644
--- a/Documentation/core-api/workqueue.rst
+++ b/Documentation/core-api/workqueue.rst
@@ -177,8 +177,9 @@ resources, scheduled and executed.
   workqueues are always per-CPU and all BH work items are executed in the
   queueing CPU's softirq context in the queueing order.
 
-  All BH workqueues must have 0 ``max_active`` and ``WQ_HIGHPRI`` is the
-  only allowed additional flag.
+  All BH workqueues must have 0 ``max_active``. ``WQ_HIGHPRI`` and
+  ``WQ_PERCPU`` are the only permitted flags. ``WQ_PERCPU`` is enforced by
+  default as BH workqueueus cannot be unbound.
 
   BH work items cannot sleep. All other features such as delayed queueing,
   flushing and canceling are supported.
@@ -206,6 +207,10 @@ resources, scheduled and executed.
   * Long running CPU intensive workloads which can be better
     managed by the system scheduler.
 
+  Workqueue without ``WQ_PERCPU`` are unbound by default, with the
+  exception of ``WQ_BH`` workqueues, which always have ``WQ_PERCPU``
+  set since they can't be unbound.
+
 ``WQ_FREEZABLE``
   A freezable wq participates in the freeze phase of the system
   suspend operations.  Work items on the wq are drained and no
-- 
2.55.0