[PATCH] workqueue: Add RCU annotation for pwq list walk

[PATCH] workqueue: Add RCU annotation for pwq list walk

[Sebastian Andrzej Siewior]

An additional check has been recently added to ensure that a RCU related lock
is held while the RCU list is iterated.
The `pwqs' are sometimes iterated without a RCU lock but with the &wq->mutex
acquired leading to a warning.

Teach list_for_each_entry_rcu() that the RCU usage is okay if &wq->mutex
is acquired during the list traversal.

Fixes: 28875945ba98d ("rcu: Add support for consolidated-RCU reader checking")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/workqueue.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index bc2e09a8ea61d..0a1d2f4289178 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -425,7 +425,8 @@ static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
  * ignored.
  */
 #define for_each_pwq(pwq, wq)						\
-	list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node)		\
+	list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node,		\
+				lockdep_is_held(&wq->mutex))		\
 		if (({ assert_rcu_or_wq_mutex(wq); false; })) { }	\
 		else
 
-- 
2.24.0

Re: [PATCH] workqueue: Add RCU annotation for pwq list walk

[Tejun Heo]

On Fri, Nov 15, 2019 at 07:01:25PM +0100, Sebastian Andrzej Siewior wrote:
> An additional check has been recently added to ensure that a RCU related lock
> is held while the RCU list is iterated.
> The `pwqs' are sometimes iterated without a RCU lock but with the &wq->mutex
> acquired leading to a warning.
> 
> Teach list_for_each_entry_rcu() that the RCU usage is okay if &wq->mutex
> is acquired during the list traversal.
> 
> Fixes: 28875945ba98d ("rcu: Add support for consolidated-RCU reader checking")
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Applied to wq/for-5.5.

Thanks.

-- 
tejun