From 3678d62f028689abc8ac5693b254e48f605f94ba Mon Sep 17 00:00:00 2001 From: Corey Minyard Date: Sat, 10 Feb 2007 01:45:42 -0800 Subject: [PATCH] [PATCH] add an RCU version of list splicing This patch is in support of the IPMI driver. I have tested this with the IPMI driver changes coming in the next patch. Add a list_splice_init_rcu() function to splice an RCU-protected list into another list. This takes the sync function as an argument, so one would do something like: INIT_LIST_HEAD(&list); list_splice_init_rcu(&source, &dest, synchronize_rcu); The idea being to keep the RCU API proliferation down to a dull roar. [akpm@osdl.org: build fix] Signed-off-by: Paul E. McKenney Signed-off-by: Corey Minyard Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/list.h | 56 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 56 insertions(+) diff --git a/include/linux/list.h b/include/linux/list.h index 611059d633f..cdc96559e5a 100644 --- a/include/linux/list.h +++ b/include/linux/list.h @@ -359,6 +359,62 @@ static inline void list_splice_init(struct list_head *list, } } +/** + * list_splice_init_rcu - splice an RCU-protected list into an existing list. + * @list: the RCU-protected list to splice + * @head: the place in the list to splice the first list into + * @sync: function to sync: synchronize_rcu(), synchronize_sched(), ... + * + * @head can be RCU-read traversed concurrently with this function. + * + * Note that this function blocks. + * + * Important note: the caller must take whatever action is necessary to + * prevent any other updates to @head. In principle, it is possible + * to modify the list as soon as sync() begins execution. + * If this sort of thing becomes necessary, an alternative version + * based on call_rcu() could be created. But only if -really- + * needed -- there is no shortage of RCU API members. + */ +static inline void list_splice_init_rcu(struct list_head *list, + struct list_head *head, + void (*sync)(void)) +{ + struct list_head *first = list->next; + struct list_head *last = list->prev; + struct list_head *at = head->next; + + if (list_empty(head)) + return; + + /* "first" and "last" tracking list, so initialize it. */ + + INIT_LIST_HEAD(list); + + /* + * At this point, the list body still points to the source list. + * Wait for any readers to finish using the list before splicing + * the list body into the new list. Any new readers will see + * an empty list. + */ + + sync(); + + /* + * Readers are finished with the source list, so perform splice. + * The order is important if the new list is global and accessible + * to concurrent RCU readers. Note that RCU readers are not + * permitted to traverse the prev pointers without excluding + * this function. + */ + + last->next = at; + smp_wmb(); + head->next = first; + first->prev = head; + at->prev = last; +} + /** * list_entry - get the struct for this entry * @ptr: the &struct list_head pointer. -- 2.41.1