Re: [Openipmi-developer] [PATCH] IPMI: fix some RCU problems
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From: Paul E. M. <pa...@li...> - 2006-12-28 22:24:26
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On Thu, Dec 28, 2006 at 12:24:22PM -0800, Randy Dunlap wrote: > On Thu, 28 Dec 2006 11:55:04 -0800 Paul E. McKenney wrote: > > > list.h | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 58 insertions(+) > > > > diff -urpNa -X dontdiff linux-2.6.19/include/linux/list.h linux-2.6.19-lpr/include/linux/list.h > > --- linux-2.6.19/include/linux/list.h 2006-11-29 13:57:37.000000000 -0800 > > +++ linux-2.6.19-lpr/include/linux/list.h 2006-12-28 11:48:31.000000000 -0800 > > @@ -360,6 +360,64 @@ static inline void list_splice_init(stru > > } > > > > /** > > + * 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(), ... > > @parameter: is kernel-doc syntax. > I.e., please add a colon after each one of those. Good point! :-/ Fixed below. Signed-off-by: Paul E. McKenney <pa...@li...> --- list.h | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 58 insertions(+) diff -urpNa -X dontdiff linux-2.6.19/include/linux/list.h linux-2.6.19-lpr/include/linux/list.h --- linux-2.6.19/include/linux/list.h 2006-11-29 13:57:37.000000000 -0800 +++ linux-2.6.19-lpr/include/linux/list.h 2006-12-28 14:21:05.000000000 -0800 @@ -360,6 +360,64 @@ static inline void list_splice_init(stru } /** + * 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; + + might_sleep(); + 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. * @type: the type of the struct this is embedded in. |