From: Paul E. McKenney Date: Fri, 20 Aug 2010 04:43:09 +0000 (-0700) Subject: rcu: add comment stating that list_empty() applies to RCU-protected lists X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=65e6bf484c497f02d47a0faae69ee398cd59cfda;p=openwrt%2Fstaging%2Fblogic.git 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 --- 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