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

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Message-ID: <20191115180125.j4gvmltzi6z2szhw@linutronix.de>
Date:   Fri, 15 Nov 2019 19:01:25 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Joel Fernandes <joel@...lfernandes.org>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] workqueue: Add RCU annotation for pwq list walk

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@...utronix.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