Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH tip/core/rcu 7/7] rcu: add comment stating that list_empty() applies to RCU-protected lists | Date | Fri, 20 Aug 2010 11:45:45 -0700 |
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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@linux-foundation.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> --- 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 */ -- 1.7.0.6
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