Commit-ID: 65e6bf484c497f02d47a0faae69ee398cd59cfda Gitweb: http://git.kernel.org/tip/65e6bf484c497f02d47a0faae69ee398cd59cfda Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> AuthorDate: Thu, 19 Aug 2010 21:43:09 -0700 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Fri, 20 Aug 2010 09:00:18 -0700 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 <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> --- include/linux/rculist.h | 9 +++++++++ 1 files changed, 9 insertions(+), 0 deletions(-) diff --git a/include/linux/rculist.h b/include/linux/rculist.h index c10b105..f31ef61 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -10,6 +10,15 @@ #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(). + */ + +/* * return the ->next pointer of a list_head in an rcu safe * way, we must not access it directly */ -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
|