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SubjectRe: [PATCH] seq_file: add RCU versions of new hlist/list iterators
On Thu, Feb 18, 2010 at 03:30:41PM -0800, Stephen Hemminger wrote:
> Many usages of seq_file use RCU protected lists, so non RCU
> iterators will not work safely.

Can't say that I am thrilled by the use of __list_for_each_rcu() and the
creation of __hlist_for_each(), but given the seq_list API, I don't see
a reasonable alternative. So...

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
>
> ---
> fs/seq_file.c | 82 +++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/rculist.h | 5 ++
> include/linux/seq_file.h | 27 ++++++++++-----
> 3 files changed, 105 insertions(+), 9 deletions(-)
>
> --- a/fs/seq_file.c 2010-02-18 15:08:53.228872265 -0800
> +++ b/fs/seq_file.c 2010-02-18 15:26:21.157402219 -0800
> @@ -695,6 +695,38 @@ struct list_head *seq_list_next(void *v,
> }
> EXPORT_SYMBOL(seq_list_next);
>
> +struct list_head *seq_list_start_rcu(struct list_head *head, loff_t pos)
> +{
> + struct list_head *lh;
> +
> + __list_for_each_rcu(lh, head)
> + if (pos-- == 0)
> + return lh;
> +
> + return NULL;
> +}
> +EXPORT_SYMBOL(seq_list_start_rcu);
> +
> +struct list_head *seq_list_start_head_rcu(struct list_head *head, loff_t pos)
> +{
> + if (!pos)
> + return head;
> +
> + return seq_list_start_rcu(head, pos - 1);
> +}
> +EXPORT_SYMBOL(seq_list_start_head_rcu);
> +
> +struct list_head *seq_list_next_rcu(void *v, struct list_head *head,
> + loff_t *ppos)
> +{
> + struct list_head *lh = v;
> +
> + lh = rcu_dereference(lh->next);
> + ++*ppos;
> + return lh == head ? NULL : lh;
> +}
> +EXPORT_SYMBOL(seq_list_next_rcu);
> +
> /**
> * seq_hlist_start - start an iteration of a hlist
> * @head: the head of the hlist
> @@ -750,3 +782,53 @@ struct hlist_node *seq_hlist_next(void *
> return node->next;
> }
> EXPORT_SYMBOL(seq_hlist_next);
> +
> +/**
> + * seq_hlist_start_rcu - start an iteration of a hlist protected by RCU
> + * @head: the head of the hlist
> + * @pos: the start position of the sequence
> + *
> + * Called at seq_file->op->start().
> + */
> +struct hlist_node *seq_hlist_start_rcu(struct hlist_head *head, loff_t pos)
> +{
> + struct hlist_node *node;
> +
> + __hlist_for_each_rcu(node, head)
> + if (pos-- == 0)
> + return node;
> + return NULL;
> +}
> +EXPORT_SYMBOL(seq_hlist_start_rcu);
> +
> +/**
> + * seq_hlist_start_head_rcu - start an iteration of a hlist protected by RCU
> + * @head: the head of the hlist
> + * @pos: the start position of the sequence
> + *
> + * Called at seq_file->op->start(). Call this function if you want to
> + * print a header at the top of the output.
> + */
> +struct hlist_node *seq_hlist_start_head_rcu(struct hlist_head *head, loff_t pos)
> +{
> + if (!pos)
> + return SEQ_START_TOKEN;
> +
> + return seq_hlist_start_rcu(head, pos - 1);
> +}
> +EXPORT_SYMBOL(seq_hlist_start_rcu);
> +
> +/**
> + * seq_hlist_next_rcu - move to the next position of the hlist protected by RCU
> + * @v: the current iterator
> + * @head: the head of the hlist
> + * @pos: the current posision
> + *
> + * Called at seq_file->op->next().
> + */
> +struct hlist_node *seq_hlist_next_rcu(void *v, struct hlist_head *head,
> + loff_t *ppos)
> +{
> + return rcu_dereference(seq_hlist_next(v, head, ppos));
> +}
> +EXPORT_SYMBOL(seq_hlist_next_rcu);
> --- a/include/linux/seq_file.h 2010-02-18 15:08:53.256872028 -0800
> +++ b/include/linux/seq_file.h 2010-02-18 15:09:14.128997914 -0800
> @@ -127,23 +127,32 @@ int seq_release_private(struct inode *,
> /*
> * Helpers for iteration over list_head-s in seq_files
> */
> -
> extern struct list_head *seq_list_start(struct list_head *head,
> - loff_t pos);
> + loff_t pos);
> extern struct list_head *seq_list_start_head(struct list_head *head,
> - loff_t pos);
> + loff_t pos);
> extern struct list_head *seq_list_next(void *v, struct list_head *head,
> - loff_t *ppos);
> -
> + loff_t *ppos);
> +extern struct list_head *seq_list_start_rcu(struct list_head *head,
> + loff_t pos);
> +extern struct list_head *seq_list_start_head_rcu(struct list_head *head,
> + loff_t pos);
> +extern struct list_head *seq_list_next_rcu(void *v, struct list_head *head,
> + loff_t *ppos);
> /*
> * Helpers for iteration over hlist_head-s in seq_files
> */
> -
> extern struct hlist_node *seq_hlist_start(struct hlist_head *head,
> - loff_t pos);
> + loff_t pos);
> extern struct hlist_node *seq_hlist_start_head(struct hlist_head *head,
> - loff_t pos);
> + loff_t pos);
> extern struct hlist_node *seq_hlist_next(void *v, struct hlist_head *head,
> - loff_t *ppos);
> + loff_t *ppos);
>
> +extern struct hlist_node *seq_hlist_start_rcu(struct hlist_head *head,
> + loff_t pos);
> +extern struct hlist_node *seq_hlist_start_head_rcu(struct hlist_head *head,
> + loff_t pos);
> +extern struct hlist_node *seq_hlist_next_rcu(void *v, struct hlist_head *head,
> + loff_t *ppos);
> #endif
> --- a/include/linux/rculist.h 2010-02-18 15:25:03.681496691 -0800
> +++ b/include/linux/rculist.h 2010-02-18 15:26:13.909286656 -0800
> @@ -406,6 +406,11 @@ static inline void hlist_add_after_rcu(s
> n->next->pprev = &n->next;
> }
>
> +#define __hlist_for_each(pos, head) \
> + for (pos = rcu_dereference((head)->first); \
> + pos && ({ prefetch(pos->next); 1; }); \
> + pos = rcu_derference(pos->next))
> +
> /**
> * hlist_for_each_entry_rcu - iterate over rcu list of given type
> * @tpos: the type * to use as a loop cursor.


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