linux-kernel - [PATCH] rculist: unify documentation about missing list_empty

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Date:   Fri, 21 May 2021 12:08:29 +0200
From:   Julian Wiedmann <jwi@...ux.ibm.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>
Cc:     Julian Wiedmann <jwi@...ux.ibm.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] rculist: unify documentation about missing list_empty_rcu()

We have two separate sections that talk about why list_empty_rcu()
is not needed, consolidate them.

Signed-off-by: Julian Wiedmann <jwi@...ux.ibm.com>
---
 include/linux/rculist.h | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index f8633d37e358..f8f42ce04382 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -10,15 +10,6 @@
 #include <linux/list.h>
 #include <linux/rcupdate.h>
 
-/*
- * Why is there no list_empty_rcu()?  Because list_empty() serves this
- * purpose.  The list_empty() function fetches the RCU-protected pointer
- * and compares it to the address of the list head, but neither dereferences
- * this pointer itself nor provides this pointer to the caller.  Therefore,
- * it is not necessary to use rcu_dereference(), so that list_empty() can
- * be used anywhere you would want to use a list_empty_rcu().
- */
-
 /*
  * INIT_LIST_HEAD_RCU - Initialize a list_head visible to RCU readers
  * @list: list to be initialized
@@ -334,6 +325,12 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  * list_first_entry() because they would be protected by a lock that blocks
  * writers.
  *
+ * list_empty() fetches the RCU-protected pointer and compares it to the address
+ * of the list head. But it neither dereferences this pointer itself, nor
+ * provides this pointer to the caller. Therefore it is not necessary to use
+ * rcu_dereference(), and list_empty() can be used anywhere you would want to
+ * use a list_empty_rcu().
+ *
  * See list_first_or_null_rcu for an alternative.
  */
 
-- 
2.25.1