From 65e6bf484c497f02d47a0faae69ee398cd59cfda Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 19 Aug 2010 21:43:09 -0700 Subject: [PATCH] rcu: add comment stating that list_empty() applies to RCU-protected lists Because list_empty() does not dereference any RCU-protected pointers, and further does not pass such pointers to the caller (so that the caller does not dereference them either), it is safe to use list_empty() on RCU-protected lists. There is no need for a list_empty_rcu(). This commit adds a comment stating this explicitly. Requested-by: Andrew Morton Signed-off-by: Paul E. McKenney --- include/linux/rculist.h | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/include/linux/rculist.h b/include/linux/rculist.h index c10b1050dbe6..f31ef61f1c65 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -9,6 +9,15 @@ #include #include +/* + * 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(). + */ + /* * return the ->next pointer of a list_head in an rcu safe * way, we must not access it directly -- 2.20.1