More explicitly state what is, and what is not guaranteed to those who iterate a list while protected by RCU. Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> --- Documentation/RCU/listRCU.rst | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/Documentation/RCU/listRCU.rst b/Documentation/RCU/listRCU.rst index bdc4bcc5289f..aff1394f6d93 100644 --- a/Documentation/RCU/listRCU.rst +++ b/Documentation/RCU/listRCU.rst @@ -8,6 +8,18 @@ One of the most common uses of RCU is protecting read-mostly linked lists that all of the required memory ordering is provided by the list macros. This document describes several list-based RCU use cases. +When iterating a list while holding the rcu_read_lock(), writers may +modify the list. The reader is guaranteed to see all of the elements +which were added to the list before they acquired the rcu_read_lock() +and are still on the list when they drop the rcu_read_unlock(). +Elements which are added to, or removed from the list may or may not +be seen. If the writer calls list_replace_rcu(), the reader may see +either the old element or the new element; they will not see both, +nor will they see neither. + +There is no equivalent of list_for_each_entry_reverse(); RCU lists +may only be walked forwards. + Example 1: Read-mostly list: Deferred Destruction ------------------------------------------------- -- 2.40.1
